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2016 Volume 32 Issue 7
2016, 32(7):
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2016, 32(7): 1549-1550
doi: 10.3866/PKU.WHXB201606221
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2016, 32(7): 1551-1552
doi: 10.3866/PKU.WHXB201606171
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2016, 32(7): 1553-1553
doi: 10.3866/PKU.WHXB201606241
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2016, 32(7): 1554-1555
doi: 10.3866/PKU.WHXB201606201
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2016, 32(7): 1556-1592
doi: 10.3866/PKU.WHXB201604291
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Because of its zero-carbon emission energy, hydrogen energy is considered the cleanest energy. The greatest challenge is to develop a cost-effective strategy for hydrogen generation. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion are promising pathways for sustainable hydrogen production. All of these techniques require highly active noble metal-free hydrogen and oxygen evolution catalysts to make the water splitting process energy efficient and economical. In this review, we highlight recent research efforts toward synthesis and performance optimization of noble metal-free electrocatalysts in our institute over the last 3 years. We focus on (1) hydrogen evolution catalysts, including transition metal phosphide, sulfides, selenides, and carbides; (2) oxygen evolution catalysts, including transition metal phosphide, sulfide, and oxide/hydroxides; and (3) bifunctional catalysts, mainly comprising transition metal phosphides, selenides, sulfides, and so on. Finally, we summarize the challenges and prospective for future development of non-noble metal catalysts for water electrolysis.
Because of its zero-carbon emission energy, hydrogen energy is considered the cleanest energy. The greatest challenge is to develop a cost-effective strategy for hydrogen generation. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion are promising pathways for sustainable hydrogen production. All of these techniques require highly active noble metal-free hydrogen and oxygen evolution catalysts to make the water splitting process energy efficient and economical. In this review, we highlight recent research efforts toward synthesis and performance optimization of noble metal-free electrocatalysts in our institute over the last 3 years. We focus on (1) hydrogen evolution catalysts, including transition metal phosphide, sulfides, selenides, and carbides; (2) oxygen evolution catalysts, including transition metal phosphide, sulfide, and oxide/hydroxides; and (3) bifunctional catalysts, mainly comprising transition metal phosphides, selenides, sulfides, and so on. Finally, we summarize the challenges and prospective for future development of non-noble metal catalysts for water electrolysis.
2016, 32(7): 1593-1603
doi: 10.3866/PKU.WHXB201605231
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Owing to advantages such as high theoretical specific capacity, designable structure, low cost and environmental friendliness, organic quinone compounds have been proposed as promising electrode materials for rechargeable lithium batteries. In this review, we first introduce the classification, structural characteristics, electrochemical reaction mechanism and performance of quinone-based electrodes. We then summarize the recent progress, existing problems and strategies for improving the electrochemical performance of quinonebased compounds and polymers. Finally, we also discuss the future development of such materials for use in lithium batteries.
Owing to advantages such as high theoretical specific capacity, designable structure, low cost and environmental friendliness, organic quinone compounds have been proposed as promising electrode materials for rechargeable lithium batteries. In this review, we first introduce the classification, structural characteristics, electrochemical reaction mechanism and performance of quinone-based electrodes. We then summarize the recent progress, existing problems and strategies for improving the electrochemical performance of quinonebased compounds and polymers. Finally, we also discuss the future development of such materials for use in lithium batteries.
2016, 32(7): 1604-1622
doi: 10.3866/PKU.WHXB201604182
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Copper nanowires are excellent materials for transparent and flexible conducting electrodes in modern nanoscience and nanotechnology because of their unique optical, electrical, mechanical, and thermal properties. With the distinguishing features of relatively low price and natural abundance, copper is an ideal candidate to substitute for noble metals in technical applications. However, the main hindrances to their practical application are the susceptibility of Cu nanowires to oxidation upon exposure to air or water and the difficulty in reducing Cu ions to metallic Cu. The synthesis of copper nanowires with high monodispersity, stability, and oxidation resistance has become a major research goal. Among the wide variety of methods available to generate copper nanowires, liquid-phase reduction has been widely adopted for the advantages of high yield, simple and straightforward operation, relatively low cost, and fewer constraints on reaction conditions, in addition to solving the above problems. This review begins with an introduction to the research background and significance of copper nanowires. First, we present a brief overview of the research advances, including the synthesis and growth mechanisms, of smooth or rough, single-crystal or twinned copper nanowires. Oxidation and surface modification for oxygen-resistance are then discussed, followed by a brief summary and outlook for research in the field.
Copper nanowires are excellent materials for transparent and flexible conducting electrodes in modern nanoscience and nanotechnology because of their unique optical, electrical, mechanical, and thermal properties. With the distinguishing features of relatively low price and natural abundance, copper is an ideal candidate to substitute for noble metals in technical applications. However, the main hindrances to their practical application are the susceptibility of Cu nanowires to oxidation upon exposure to air or water and the difficulty in reducing Cu ions to metallic Cu. The synthesis of copper nanowires with high monodispersity, stability, and oxidation resistance has become a major research goal. Among the wide variety of methods available to generate copper nanowires, liquid-phase reduction has been widely adopted for the advantages of high yield, simple and straightforward operation, relatively low cost, and fewer constraints on reaction conditions, in addition to solving the above problems. This review begins with an introduction to the research background and significance of copper nanowires. First, we present a brief overview of the research advances, including the synthesis and growth mechanisms, of smooth or rough, single-crystal or twinned copper nanowires. Oxidation and surface modification for oxygen-resistance are then discussed, followed by a brief summary and outlook for research in the field.
2016, 32(7): 1623-1633
doi: 10.3866/PKU.WHXB201604084
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The AramcoMech 1.3 mechanism, containing 253 species and 1542 reactions for oxidation of hydrocarbon and oxygenated C1-C2 fuels, is reduced with six direct relation graph (DRG)-related methods. The final skeletal mechanism with 81 species and 497 reactions is achieved from the intersection of the resulting skeletal mechanisms obtained with these DRG-related methods. The maximum error for the ignition delay times with this 81-species mechanism does not increase significantly compared with that obtained for the other skeletal mechanisms. This shows that the intersection of skeletal mechanisms from various mechanism reduction methods can effectively remove the redundant species. Ignition delay times of two-component mixtures with the skeletal mechanism also agree very well with those of the detailed mechanism. The skeletal mechanism has also been validated against the detailed mechanism using many other combustion characters of the involved fuels in different reactors and flames. Results from the element flux analysis demonstrate that the reaction paths for these fuels with the detailed mechanism can be reproduced accurately with the 81-species skeletal mechanism. All the important reaction paths are thus retained in the 81-species mechanism. All these results show that the skeletal mechanism is able to provide the combustion properties of C1-C2 fuels that are in good agreement with those of the detailed mechanism. The 81-species skeletal mechanism can be employed as a reaction base for developing mechanisms of other large hydrocarbon or oxygenated fuels.
The AramcoMech 1.3 mechanism, containing 253 species and 1542 reactions for oxidation of hydrocarbon and oxygenated C1-C2 fuels, is reduced with six direct relation graph (DRG)-related methods. The final skeletal mechanism with 81 species and 497 reactions is achieved from the intersection of the resulting skeletal mechanisms obtained with these DRG-related methods. The maximum error for the ignition delay times with this 81-species mechanism does not increase significantly compared with that obtained for the other skeletal mechanisms. This shows that the intersection of skeletal mechanisms from various mechanism reduction methods can effectively remove the redundant species. Ignition delay times of two-component mixtures with the skeletal mechanism also agree very well with those of the detailed mechanism. The skeletal mechanism has also been validated against the detailed mechanism using many other combustion characters of the involved fuels in different reactors and flames. Results from the element flux analysis demonstrate that the reaction paths for these fuels with the detailed mechanism can be reproduced accurately with the 81-species skeletal mechanism. All the important reaction paths are thus retained in the 81-species mechanism. All these results show that the skeletal mechanism is able to provide the combustion properties of C1-C2 fuels that are in good agreement with those of the detailed mechanism. The 81-species skeletal mechanism can be employed as a reaction base for developing mechanisms of other large hydrocarbon or oxygenated fuels.
2016, 32(7): 1634-1638
doi: 10.3866/PKU.WHXB201605111
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In the present work, graphene samples were obtained from graphene oxide (GO) by a direct hydrothermal method, using thermogravimetry-differential thermal analysis to ascertain changes in mass as well as the oxidization temperature. Thermal analysis-mass spectrometry was also used to assess the generation of H2O+ (m/z = 18) and CO2+ (m/z = 44) ions over the temperature range of 400-650 ℃. On the basis of the resulting data, the mass loss of the GO during the oxidation process is attributed to the loss of H2O and CO2. The thermal kinetics of graphene under ambient air were also studied at heating rates of 5, 10, and 15 ℃·min-1. The activation energy (Ea) and logarithm of pre-exponential factor (lg(A/s-1)) values calculated by the Kissinger method were 155.11 kJ·mol-1 and 6.90. The dependence of Ea and lgA on the extent of conversion,α, were also calculated, using the Ozawa-Flynn-Wall (FWO) method. The results of this work provide a frame of reference for the use of graphene in thermal applications, such as in thermal interface and thermal conductive materials, advanced composites and materials synthesis.
In the present work, graphene samples were obtained from graphene oxide (GO) by a direct hydrothermal method, using thermogravimetry-differential thermal analysis to ascertain changes in mass as well as the oxidization temperature. Thermal analysis-mass spectrometry was also used to assess the generation of H2O+ (m/z = 18) and CO2+ (m/z = 44) ions over the temperature range of 400-650 ℃. On the basis of the resulting data, the mass loss of the GO during the oxidation process is attributed to the loss of H2O and CO2. The thermal kinetics of graphene under ambient air were also studied at heating rates of 5, 10, and 15 ℃·min-1. The activation energy (Ea) and logarithm of pre-exponential factor (lg(A/s-1)) values calculated by the Kissinger method were 155.11 kJ·mol-1 and 6.90. The dependence of Ea and lgA on the extent of conversion,α, were also calculated, using the Ozawa-Flynn-Wall (FWO) method. The results of this work provide a frame of reference for the use of graphene in thermal applications, such as in thermal interface and thermal conductive materials, advanced composites and materials synthesis.
2016, 32(7): 1639-1648
doi: 10.3866/PKU.WHXB201604062
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The relationship between the bond angle and bond dipole moment is investigated. The atomic dipole moment corrected Hirshfeld (ADCH) charges are used to calculate the bond dipole moment. The electron localization function and its values at the bond critical points are exploited to analyze the bond′s electronic structures. Through analyzing the data of a series of covalent compounds formed by the IVA (IVA = C, Si, Ge), VA (VA = N, P, As), VIA (VIA = O, S, Se) and VIIA (VIIA = F, Cl, Br) group elements, it is found that, owing to the repulsion of bond dipole moments, the bond angles of these molecules become larger as their corresponding bond dipole moments increase if the bonds′ electronic structures are similar. This observation is also true for the ring molecules studied here, although a stress exists within the ring.
The relationship between the bond angle and bond dipole moment is investigated. The atomic dipole moment corrected Hirshfeld (ADCH) charges are used to calculate the bond dipole moment. The electron localization function and its values at the bond critical points are exploited to analyze the bond′s electronic structures. Through analyzing the data of a series of covalent compounds formed by the IVA (IVA = C, Si, Ge), VA (VA = N, P, As), VIA (VIA = O, S, Se) and VIIA (VIIA = F, Cl, Br) group elements, it is found that, owing to the repulsion of bond dipole moments, the bond angles of these molecules become larger as their corresponding bond dipole moments increase if the bonds′ electronic structures are similar. This observation is also true for the ring molecules studied here, although a stress exists within the ring.
Mesoscopic Structure of Nafion-Ionic Liquid Membrane Using Dissipative Particle Dynamics Simulations
2016, 32(7): 1649-1657
doi: 10.3866/PKU.WHXB2016032804
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The mesoscopic structure of Nafion-[Bmim][TfO] ionic liquid (IL) composite membrane was studied using dissipative particle dynamics (DPD) simulations. The effects of temperature and IL concentration on the mesoscopic structure were investigated. Microphase-separation phenomena were observed. Analyses of the pore size distributions under different conditions indicated that with the increasing IL concentration in composite membrane, the aggregated state was transformed from dispersed IL clusters to coherent IL channels. A chamber structure was formed when the IL concentration was very high. The structure of ionic liquid channels became more complex with increasing temperature and the chamber was transformed into new branches of channels, indicating that the IL channels became more coherent at elevated temperatures. The interfacial distribution probabilities and radial distribution functions indicated that the alkyl chains of ionic liquids were embedded in the Nafion backbone, and changes in the distribution of sulfonic acid groups in the side chains directly affected the distribution of imidazole groups and anions at the microphase interface. In this work, the mesoscopic structures of Nafion-IL composite membrane at the molecular level were explored and valuable insights for developing new high-temperature proton-conducting polyelectrolyte materials were obtained.
The mesoscopic structure of Nafion-[Bmim][TfO] ionic liquid (IL) composite membrane was studied using dissipative particle dynamics (DPD) simulations. The effects of temperature and IL concentration on the mesoscopic structure were investigated. Microphase-separation phenomena were observed. Analyses of the pore size distributions under different conditions indicated that with the increasing IL concentration in composite membrane, the aggregated state was transformed from dispersed IL clusters to coherent IL channels. A chamber structure was formed when the IL concentration was very high. The structure of ionic liquid channels became more complex with increasing temperature and the chamber was transformed into new branches of channels, indicating that the IL channels became more coherent at elevated temperatures. The interfacial distribution probabilities and radial distribution functions indicated that the alkyl chains of ionic liquids were embedded in the Nafion backbone, and changes in the distribution of sulfonic acid groups in the side chains directly affected the distribution of imidazole groups and anions at the microphase interface. In this work, the mesoscopic structures of Nafion-IL composite membrane at the molecular level were explored and valuable insights for developing new high-temperature proton-conducting polyelectrolyte materials were obtained.
2016, 32(7): 1658-1665
doi: 10.3866/PKU.WHXB201604111
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The first-principles plane-wave pseudopotential method within density functional theory formalism is used to investigate the effect of Y atom decoration of graphene on the properties for hydrogen storage. The clustering problem for the Y atoms decorated on graphene is considered, and substitutional boron doping is shown to effectively prevent the clustering of Y atoms on graphene. The geometrical configuration of the modified system is stable and the adsorption properties of H2 are excellent, which can adsorb up to 6 H2 molecules with an average adsorption energy range of -0.539 to -0.655 eV (per H2), as determined by theoretical analyses. This satisfies the theoretical ideal range for hydrogen storage. Moreover, based on the calculation and analysis of the Bader charge, the electronic density of states and the charge density difference of the H2/Y/B/graphene (G) system, it is proved that the Y atom exhibits bonding with graphene by charge transfer and interacts with hydrogen molecules through typical Kubas interactions. The existence of the Y atomalters the charge distribution of the H2 molecules and graphene sheet. Hence, the Y atom becomes a bridge linking the H2 molecules and graphene sheet. Thereby, the adsorption energies of the H2 molecule are adjusted to the reasonable region. The modified system exhibits excellent potential as one of the most suitable candidates for a hydrogen storage medium in the molecular state at near ambient conditions.
The first-principles plane-wave pseudopotential method within density functional theory formalism is used to investigate the effect of Y atom decoration of graphene on the properties for hydrogen storage. The clustering problem for the Y atoms decorated on graphene is considered, and substitutional boron doping is shown to effectively prevent the clustering of Y atoms on graphene. The geometrical configuration of the modified system is stable and the adsorption properties of H2 are excellent, which can adsorb up to 6 H2 molecules with an average adsorption energy range of -0.539 to -0.655 eV (per H2), as determined by theoretical analyses. This satisfies the theoretical ideal range for hydrogen storage. Moreover, based on the calculation and analysis of the Bader charge, the electronic density of states and the charge density difference of the H2/Y/B/graphene (G) system, it is proved that the Y atom exhibits bonding with graphene by charge transfer and interacts with hydrogen molecules through typical Kubas interactions. The existence of the Y atomalters the charge distribution of the H2 molecules and graphene sheet. Hence, the Y atom becomes a bridge linking the H2 molecules and graphene sheet. Thereby, the adsorption energies of the H2 molecule are adjusted to the reasonable region. The modified system exhibits excellent potential as one of the most suitable candidates for a hydrogen storage medium in the molecular state at near ambient conditions.
2016, 32(7): 1666-1673
doi: 10.3866/PKU.WHXB201604012
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Density functional theory with dispersion correction (DFT-D3) was used to investigate the effects of N-doping on the adsorption of CO2 in carbonaceous materials. The CO2 adsorption energies and equilibrium geometry parameters were studied to compare the effects of various N-containing functional groups. The adsorption energies of single amide-and pyridine-type adsorbents were higher than those of aniline-and pyrroletype adsorbents, as a result of strong electrostatic interactions and/or the formation of weak hydrogen bonds. For pyrrole-type adsorbents, the adsorption energy increased with increasing number of benzene rings, because dispersion became the dominant interaction. These findings indicate that amide-and pyrrole-type adsorbents are the most promising CO2 trappers. The calculation results are consistent with our previous experimental conclusions for N-doped carbonaceous materials and will be useful for screening carbon materials to achieve more efficient CO2 capture.
Density functional theory with dispersion correction (DFT-D3) was used to investigate the effects of N-doping on the adsorption of CO2 in carbonaceous materials. The CO2 adsorption energies and equilibrium geometry parameters were studied to compare the effects of various N-containing functional groups. The adsorption energies of single amide-and pyridine-type adsorbents were higher than those of aniline-and pyrroletype adsorbents, as a result of strong electrostatic interactions and/or the formation of weak hydrogen bonds. For pyrrole-type adsorbents, the adsorption energy increased with increasing number of benzene rings, because dispersion became the dominant interaction. These findings indicate that amide-and pyrrole-type adsorbents are the most promising CO2 trappers. The calculation results are consistent with our previous experimental conclusions for N-doped carbonaceous materials and will be useful for screening carbon materials to achieve more efficient CO2 capture.
2016, 32(7): 1674-1680
doi: 10.3866/PKU.WHXB2016032806
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Au catalysts supported on an oxide show excellent activity in CO oxidation under moderate conditions. Many experiments and theoretical calculations have shown the important role of the interface between Au and the oxide support during CO oxidation. Inverse catalysts provide an alternative way to probe the role of the interface. We used Al2O3/Au(111) as a model inverse catalyst in this study, and used density functional theory to investigate the properties of Al2O3/Au(111), the interface between Al2O3 and Au(111), the adsorption of O2, and CO oxidation over Al2O3/Au(111). Our theoretical calculations show that small Al2O3 clusters are strongly bound on the Au(111) surface as a result of charge transfer. The results for O2 adsorption on different sites indicate that the interfacial site is the most stable one because of simultaneous bonding of O2 with Au and Al atoms. The full catalytic cycles for CO oxidation by O2 by either an association or dissociation pathway were investigated. Oxidation in the association pathway is significantly easier than that in the dissociation one; the participation of CO makes dissociation of the adsorbed O2 easier. This study reveals not only the origin of inverse catalysts for CO oxidation but also the role of the interface in CO oxidation on Au catalysts.
Au catalysts supported on an oxide show excellent activity in CO oxidation under moderate conditions. Many experiments and theoretical calculations have shown the important role of the interface between Au and the oxide support during CO oxidation. Inverse catalysts provide an alternative way to probe the role of the interface. We used Al2O3/Au(111) as a model inverse catalyst in this study, and used density functional theory to investigate the properties of Al2O3/Au(111), the interface between Al2O3 and Au(111), the adsorption of O2, and CO oxidation over Al2O3/Au(111). Our theoretical calculations show that small Al2O3 clusters are strongly bound on the Au(111) surface as a result of charge transfer. The results for O2 adsorption on different sites indicate that the interfacial site is the most stable one because of simultaneous bonding of O2 with Au and Al atoms. The full catalytic cycles for CO oxidation by O2 by either an association or dissociation pathway were investigated. Oxidation in the association pathway is significantly easier than that in the dissociation one; the participation of CO makes dissociation of the adsorbed O2 easier. This study reveals not only the origin of inverse catalysts for CO oxidation but also the role of the interface in CO oxidation on Au catalysts.
2016, 32(7): 1681-1690
doi: 10.3866/PKU.WHXB201605093
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Crown ethers have been widely used for lithium separation in practical applications due to their selectivity. In this study, model crown ethers having different cavity sizes, donor atoms and electron donating/ withdrawing substituent groups were systematically designed. These ethers were subsequently used to study the chemical structures and thermodynamic parameters of Li+-crown ether complexes, employing density functional theory at the B3LYP/6-311+G(d,p) level. Benzo-15-crown-5 was found to have the ability to strongly coordinate lithium ions. It was determined that the coordination ability of crown ethers for lithium ions can be tuned by varying both the substituent groups and the type and amount of donor atoms. These results should be of significant benefit in developing the practical applications of crown ethers for lithium separation.
Crown ethers have been widely used for lithium separation in practical applications due to their selectivity. In this study, model crown ethers having different cavity sizes, donor atoms and electron donating/ withdrawing substituent groups were systematically designed. These ethers were subsequently used to study the chemical structures and thermodynamic parameters of Li+-crown ether complexes, employing density functional theory at the B3LYP/6-311+G(d,p) level. Benzo-15-crown-5 was found to have the ability to strongly coordinate lithium ions. It was determined that the coordination ability of crown ethers for lithium ions can be tuned by varying both the substituent groups and the type and amount of donor atoms. These results should be of significant benefit in developing the practical applications of crown ethers for lithium separation.
2016, 32(7): 1691-1698
doi: 10.3866/PKU.WHXB201604061
Abstract:
Thirty-six samples of disubstituted N-Phenyl-α-phenylnitrones, XArCH＝N(O)ArY (XPNY), were synthesized. The effects of their substituents on their reduction potentials (Ered) were investigated by systematically comparing the Ered differences for XPNY versus XArCH ＝ NArY (XBAY) and XPNY versus XArC(Me)＝NArY (XPEAY). The results show the following: there is no linear relationship between the Ered values and 13C NMR chemical shifts, δC(C＝N), of the C＝N bridging bond for XPNY; there are no linear relationships among the Ered values for XPNY versus XBAY and XPNY versus XPEAY, i.e., their Ered values show their own specific regular changes; the excited-state substituent effect of X and the indicating parameter of the metaposition group make important contributions to the Ered values of XPEAY and XBAY, but have little effect on Ered of XPNY; the excited-state substituent effect of the Y group contributes to the XPNY Ered, but rarely contributes to the Ered values of XPEAY and XBAY, and can be ignored; the parents of XBAY and XPNY have similar reduction potentials, but the reduction potential of the parent of XPEAY is lower than those of XBAY and XPNY. In general, XPEAY is more difficult to be reduced than XBAY or XPNY, for these three types of compound with X-Y group couples.
Thirty-six samples of disubstituted N-Phenyl-α-phenylnitrones, XArCH＝N(O)ArY (XPNY), were synthesized. The effects of their substituents on their reduction potentials (Ered) were investigated by systematically comparing the Ered differences for XPNY versus XArCH ＝ NArY (XBAY) and XPNY versus XArC(Me)＝NArY (XPEAY). The results show the following: there is no linear relationship between the Ered values and 13C NMR chemical shifts, δC(C＝N), of the C＝N bridging bond for XPNY; there are no linear relationships among the Ered values for XPNY versus XBAY and XPNY versus XPEAY, i.e., their Ered values show their own specific regular changes; the excited-state substituent effect of X and the indicating parameter of the metaposition group make important contributions to the Ered values of XPEAY and XBAY, but have little effect on Ered of XPNY; the excited-state substituent effect of the Y group contributes to the XPNY Ered, but rarely contributes to the Ered values of XPEAY and XBAY, and can be ignored; the parents of XBAY and XPNY have similar reduction potentials, but the reduction potential of the parent of XPEAY is lower than those of XBAY and XPNY. In general, XPEAY is more difficult to be reduced than XBAY or XPNY, for these three types of compound with X-Y group couples.
2016, 32(7): 1699-1707
doi: 10.3866/PKU.WHXB201604011
Abstract:
Ribbon-shaped mesophase pitch-based graphite fibers (MPGFs) were prepared by melt-spinning, preoxidation, carbonization, and graphitization. The effects of the size of the spinneret and spinning rate on the orientation of the carbon layers and crystal structure of the ribbon-shaped graphite fibers transverse section were investigated. The electrochemical performances of the ribbon-shaped MPGFs as anode materials for lithium-ion batteries were tested. The results show that the size of the spinneret and spinning rate significantly affect the orientation of the carbon layers. The carbon layers of graphite fibers that were prepared at a low spinning rate using a spinneret with a low length/width ratio were arranged along the radial direction. These fibers had good rate capability. Their discharge specific capacities at 0.1C and 1C rates were 336 and 300 mAh·g-1, respectively. However, the fibers showed poor cyclic performance. After 100 cycles at 0.1C rate, the capacity retention was only 89.1%. The carbon layers of the graphite fibers that were prepared at a low spinning rate using a spinneret with a high length/width ratio had a wavy, wrinkled texture and were arranged along the direction parallel to the principal plane of the fibers. These fibers had poor rate capability and excellent cyclic performance. After 100 cycles at 0.1C rate, the capacity retention was 98.8%. Meanwhile, an increase in the spinning rate causes an overall decrease in the order degree of the carbon layers of the graphite fibers, and results in a decrease of the carbon layers being arranged along the direction parallel to the principal plane of the fibers. Both these factors decrease the reversible specific capacity.
Ribbon-shaped mesophase pitch-based graphite fibers (MPGFs) were prepared by melt-spinning, preoxidation, carbonization, and graphitization. The effects of the size of the spinneret and spinning rate on the orientation of the carbon layers and crystal structure of the ribbon-shaped graphite fibers transverse section were investigated. The electrochemical performances of the ribbon-shaped MPGFs as anode materials for lithium-ion batteries were tested. The results show that the size of the spinneret and spinning rate significantly affect the orientation of the carbon layers. The carbon layers of graphite fibers that were prepared at a low spinning rate using a spinneret with a low length/width ratio were arranged along the radial direction. These fibers had good rate capability. Their discharge specific capacities at 0.1C and 1C rates were 336 and 300 mAh·g-1, respectively. However, the fibers showed poor cyclic performance. After 100 cycles at 0.1C rate, the capacity retention was only 89.1%. The carbon layers of the graphite fibers that were prepared at a low spinning rate using a spinneret with a high length/width ratio had a wavy, wrinkled texture and were arranged along the direction parallel to the principal plane of the fibers. These fibers had poor rate capability and excellent cyclic performance. After 100 cycles at 0.1C rate, the capacity retention was 98.8%. Meanwhile, an increase in the spinning rate causes an overall decrease in the order degree of the carbon layers of the graphite fibers, and results in a decrease of the carbon layers being arranged along the direction parallel to the principal plane of the fibers. Both these factors decrease the reversible specific capacity.
2016, 32(7): 1708-1714
doi: 10.3866/PKU.WHXB201604143
Abstract:
The electrochemical behavior of Pr(Ⅲ) ions was studied on a Bi-coatedWelectrode in LiCl-KCl melts by a series of techniques, such as cyclic voltammetry, square wave voltammetry, and open circuit chronopotentiometry. From the cyclic voltammogram and square wave voltammogram, the underpotential deposition of Pr(Ⅲ) on pre-deposited Bi (i.e., a Bi-coated W electrode) occurs, owing to the formation of Pr-Bi intermetallic compounds, resulting in the electrochemical reduction of Pr(Ⅲ) at less cathodic potentials than that on an inert W electrode. Using the open circuit chronopotentiometry technique, two plateaus, corresponding to the co-existence of two phases of Pr-Bi intermetallic compound, were observed. Thermodynamic properties, such as the activities and relative partial molar Gibbs energies of Pr in the Pr-Bi alloys as well as Gibbs energies of the formation for the Pr-Bi intermetallic compounds, were estimated from the open circuit potential measurement in the temperature range of 723-873 K. Pr-Bi alloys were produced on the liquid Bi pool electrode by potentiostatic electrolysis, and were characterized by X-ray diffraction (XRD) and scanning electronic microscopy with energy-dispersive spectrometry (SEM-EDS). The results indicated that the intermetallic LiClcompounds, PrBi2 and PrBi, were obtained.
The electrochemical behavior of Pr(Ⅲ) ions was studied on a Bi-coatedWelectrode in LiCl-KCl melts by a series of techniques, such as cyclic voltammetry, square wave voltammetry, and open circuit chronopotentiometry. From the cyclic voltammogram and square wave voltammogram, the underpotential deposition of Pr(Ⅲ) on pre-deposited Bi (i.e., a Bi-coated W electrode) occurs, owing to the formation of Pr-Bi intermetallic compounds, resulting in the electrochemical reduction of Pr(Ⅲ) at less cathodic potentials than that on an inert W electrode. Using the open circuit chronopotentiometry technique, two plateaus, corresponding to the co-existence of two phases of Pr-Bi intermetallic compound, were observed. Thermodynamic properties, such as the activities and relative partial molar Gibbs energies of Pr in the Pr-Bi alloys as well as Gibbs energies of the formation for the Pr-Bi intermetallic compounds, were estimated from the open circuit potential measurement in the temperature range of 723-873 K. Pr-Bi alloys were produced on the liquid Bi pool electrode by potentiostatic electrolysis, and were characterized by X-ray diffraction (XRD) and scanning electronic microscopy with energy-dispersive spectrometry (SEM-EDS). The results indicated that the intermetallic LiClcompounds, PrBi2 and PrBi, were obtained.
2016, 32(7): 1715-1721
doi: 10.3866/PKU.WHXB201604121
Abstract:
Dechlorination of 3,4,5,6-tetrachloropicolinic acid (TeCP) on roughened silver (Ag(r)) cathodes provides an unexpected example showing extraordinary catalytic effect in aqueous solution, which is counter to what has been reported in electrochemical reduction of organic halides using aprotic media. To fully recognize this extraordinary catalytic effect of silver cathodes on electrochemical reduction of 3,4,5,6-tetrachloropicolinic acid in aqueous solutions, we conduct a comprehensive study from the aspect of surface characterization, in situ electrochemical study, and theoretical calculation. Transmission electron microscopy (TEM) images and X-ray photoelectron spectroscopy (XPS) spectra are presented to observe the surface structure and chemical state of Ag(r). Experimental results show that Ag nanoparticle can be formed in the oxidation-reduction cyclic (ORC) process, which leads to an increase in the degree of surface disorder. Density functional theory (DFT) calculations of the first electron transfer (ET) process, integrated with an in situ electrochemical surfaceenhanced Raman spectroscopy (SERS) study and a cyclic voltammetry (CV) experiment with the aid of H+, were performed to characterize various surface species in different electrode potential regions. Experimental evidence shows that the first ET process is catalyzed by silver for the radical derivate (TeCP·-) formed by the ET process is adsorbed more strongly than TeCP. TeCP·- ads is the key intermediate of the dechlorination process, implying that the dechlorination mechanism could drastically differ from the outer-sphere reduction at the glass carbon (GC) electrode.
Dechlorination of 3,4,5,6-tetrachloropicolinic acid (TeCP) on roughened silver (Ag(r)) cathodes provides an unexpected example showing extraordinary catalytic effect in aqueous solution, which is counter to what has been reported in electrochemical reduction of organic halides using aprotic media. To fully recognize this extraordinary catalytic effect of silver cathodes on electrochemical reduction of 3,4,5,6-tetrachloropicolinic acid in aqueous solutions, we conduct a comprehensive study from the aspect of surface characterization, in situ electrochemical study, and theoretical calculation. Transmission electron microscopy (TEM) images and X-ray photoelectron spectroscopy (XPS) spectra are presented to observe the surface structure and chemical state of Ag(r). Experimental results show that Ag nanoparticle can be formed in the oxidation-reduction cyclic (ORC) process, which leads to an increase in the degree of surface disorder. Density functional theory (DFT) calculations of the first electron transfer (ET) process, integrated with an in situ electrochemical surfaceenhanced Raman spectroscopy (SERS) study and a cyclic voltammetry (CV) experiment with the aid of H+, were performed to characterize various surface species in different electrode potential regions. Experimental evidence shows that the first ET process is catalyzed by silver for the radical derivate (TeCP·-) formed by the ET process is adsorbed more strongly than TeCP. TeCP·- ads is the key intermediate of the dechlorination process, implying that the dechlorination mechanism could drastically differ from the outer-sphere reduction at the glass carbon (GC) electrode.
2016, 32(7): 1722-1726
doi: 10.3866/PKU.WHXB2016032807
Abstract:
The alignment of the ionic liquid (IL) cation and anion at the interface is of interest because it would affect the surface structures and properties of IL at the interfaces. In this study, Kelvin probe force microscopy (KPFM), a scanning probe microscopy technique, was used to investigate the interfacial properties of the IL at room temperature. A model molecule, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), was selectively assembled on the lyophilic chemical patterns prepared on a substrate, forming ultrathin solid-like adsorbate layers and droplets. Because the surface potential is a direct indicator of the surface dipole, which is useful for examining molecular orientation, the surface potential maps captured by KPFM indicated that the [Bmim]Cl molecules demonstrated different orientations at the gas-liquid interface (in the form of a droplet) and at the gassolid interface (in the form of a solid-like adsorbate layer). Our results indicate that KPFM has potential for the characterization of IL molecular alignment at interfaces.
The alignment of the ionic liquid (IL) cation and anion at the interface is of interest because it would affect the surface structures and properties of IL at the interfaces. In this study, Kelvin probe force microscopy (KPFM), a scanning probe microscopy technique, was used to investigate the interfacial properties of the IL at room temperature. A model molecule, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), was selectively assembled on the lyophilic chemical patterns prepared on a substrate, forming ultrathin solid-like adsorbate layers and droplets. Because the surface potential is a direct indicator of the surface dipole, which is useful for examining molecular orientation, the surface potential maps captured by KPFM indicated that the [Bmim]Cl molecules demonstrated different orientations at the gas-liquid interface (in the form of a droplet) and at the gassolid interface (in the form of a solid-like adsorbate layer). Our results indicate that KPFM has potential for the characterization of IL molecular alignment at interfaces.
2016, 32(7): 1727-1733
doi: 10.3866/PKU.WHXB201604082
Abstract:
Hierarchically porous SiO2 monoliths were prepared via sol-gel process accompanied by the phase separation and template method. The microstructure and pore structures of the monoliths were characterized, and the formation mechanism of hierarchically porous structures was investigated. The results show that the addition of poly(ethyleneoxide)-block-poly (propyleneoxide)-block-poly (ethyleneoxide) (P123) induces the phase separation to adjust the formation of the macroporous structure, and the spherical P123 micelles are also formed and distributed into the skeletons as templates. The addition of the micelle-swelling agent 1,3,5-trimethylbenzene (TMB) expands and stabilizes the P123 micelles, so that uniform spherical mesopores are successfully introduced into the macroporous framework. Meanwhile, the gel nanoparticles on the skeletons aggregate to form micropores. As a result, the hierarchically porous structures are constructed by well-defined interconnected macropores-spherical mesopores-micropores, and the corresponding porous monoliths are prepared. When the mole ratio of tetramethoxysilane (TMOS) : P123 : TMB is 1 : 0.015 : 0.353, the optimum hierarchical structure is obtained with macropore size of 0.5-1.5 μm, mesopore size of 3-4 nm on the skeleton, apparent porosity of 66.1% and Brunauer-Emmett-Teller (BET) specific surface area as high as 616 m2·g-1.
Hierarchically porous SiO2 monoliths were prepared via sol-gel process accompanied by the phase separation and template method. The microstructure and pore structures of the monoliths were characterized, and the formation mechanism of hierarchically porous structures was investigated. The results show that the addition of poly(ethyleneoxide)-block-poly (propyleneoxide)-block-poly (ethyleneoxide) (P123) induces the phase separation to adjust the formation of the macroporous structure, and the spherical P123 micelles are also formed and distributed into the skeletons as templates. The addition of the micelle-swelling agent 1,3,5-trimethylbenzene (TMB) expands and stabilizes the P123 micelles, so that uniform spherical mesopores are successfully introduced into the macroporous framework. Meanwhile, the gel nanoparticles on the skeletons aggregate to form micropores. As a result, the hierarchically porous structures are constructed by well-defined interconnected macropores-spherical mesopores-micropores, and the corresponding porous monoliths are prepared. When the mole ratio of tetramethoxysilane (TMOS) : P123 : TMB is 1 : 0.015 : 0.353, the optimum hierarchical structure is obtained with macropore size of 0.5-1.5 μm, mesopore size of 3-4 nm on the skeleton, apparent porosity of 66.1% and Brunauer-Emmett-Teller (BET) specific surface area as high as 616 m2·g-1.
2016, 32(7): 1734-1746
doi: 10.3866/PKU.WHXB201603235
Abstract:
Acomposite precipitant composed of ammonia and ammoniumcarbonate was used to prepare CeO2-ZrO2-Al2O3 (CZA). For comparison, two other CZA samples were prepared using ammonia and ammonium carbonate as the precipitants, respectively. Differences in the textural, structural and redox properties, together with the evolution upon thermal aging treatment and the catalytic performance of the corresponding Pd-only three-way catalysts, were investigated systematically. The choice of precipitant was found to affect the interactions between CeO2-ZrO2 (CZ) and Al2O3. When ammonia was used as the precipitant, the resulting CZ and Al2O3 seemed insusceptible to each other, thus the obtained CZA composite displayed inferior thermal stability due to the weakest interaction between CZ and Al2O3. In the case of ammonium carbonate, stronger interaction between CZ and Al2O3 enhanced the thermal stability of CZA, but in the meantime, the homogeneity of the CZ solid solution was severely impaired by Al2O3, leading to undesirable redox performance. Fortunately, the use of the composite precipitant brought about favorable interaction between CZ and Al2O3, leading to excellent textural and structural properties along with the highest thermal stability of the CZA compound. Consequently, the corresponding Pd-based catalyst displayed prominent reducibility and oxygen storage capacity (OSC) performance, as well as superior three-way catalytic performance.
Acomposite precipitant composed of ammonia and ammoniumcarbonate was used to prepare CeO2-ZrO2-Al2O3 (CZA). For comparison, two other CZA samples were prepared using ammonia and ammonium carbonate as the precipitants, respectively. Differences in the textural, structural and redox properties, together with the evolution upon thermal aging treatment and the catalytic performance of the corresponding Pd-only three-way catalysts, were investigated systematically. The choice of precipitant was found to affect the interactions between CeO2-ZrO2 (CZ) and Al2O3. When ammonia was used as the precipitant, the resulting CZ and Al2O3 seemed insusceptible to each other, thus the obtained CZA composite displayed inferior thermal stability due to the weakest interaction between CZ and Al2O3. In the case of ammonium carbonate, stronger interaction between CZ and Al2O3 enhanced the thermal stability of CZA, but in the meantime, the homogeneity of the CZ solid solution was severely impaired by Al2O3, leading to undesirable redox performance. Fortunately, the use of the composite precipitant brought about favorable interaction between CZ and Al2O3, leading to excellent textural and structural properties along with the highest thermal stability of the CZA compound. Consequently, the corresponding Pd-based catalyst displayed prominent reducibility and oxygen storage capacity (OSC) performance, as well as superior three-way catalytic performance.
2016, 32(7): 1747-1757
doi: 10.3866/PKU.WHXB201605103
Abstract:
A series of CeO2-ZrO2 mixed oxide catalysts having different mass ratios (wCeO2-(1-w)ZrO2) were prepared using a co-precipitation method and subsequently applied to the combustion of soot in gasoline engine exhaust. The soot combustion activities of the catalysts were assessed via the temperature-programmed oxidation of powder mixtures, applying steps of 10 ℃·min-1 from room temperature to 850 ℃. These catalysts were also characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption-desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), oxygen storage capacity (OSC), and H2 temperature-programmed reduction (H2-TPR). After being calcined at 800 ℃, 70%CeO2-30%ZrO2 exhibited the highest soot combustion activity, such that the maximum product concentration temperature (Tm) was decreased from 719 to 625 ℃ when employing this catalyst. The 70%CeO2-30%ZrO2 also showed excellent thermal stability, indicating that this could be an appropriate catalyst for soot combustion in gasoline direct injection engines. The differences in the soot combustion activities of the catalysts were closely related to their structures, surface compositions, and redox properties. XRD and Raman data demonstrated that the ceriumrich samples presented a typical cubic phase, while a tetragonal phase was observed in the case of the zirconium-rich samples. XPS showed that the molar fraction of Ce3+ in total Ce and the molar fraction of surfaceadsorbed oxygen to lattice oxygen on the surfaces of various samples differed, and these variations induced their different catalytic activities. The 70%CeO2-30%ZrO2 sample showed the largest OSC value and the most pronounced reduction properties. This same material was also found to have excellent thermal stability with regard to structure, surface composition, and redox properties, as reflected in the minimal degradation of the soot combustion activity of this catalyst with increasing calcination temperature.
A series of CeO2-ZrO2 mixed oxide catalysts having different mass ratios (wCeO2-(1-w)ZrO2) were prepared using a co-precipitation method and subsequently applied to the combustion of soot in gasoline engine exhaust. The soot combustion activities of the catalysts were assessed via the temperature-programmed oxidation of powder mixtures, applying steps of 10 ℃·min-1 from room temperature to 850 ℃. These catalysts were also characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption-desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), oxygen storage capacity (OSC), and H2 temperature-programmed reduction (H2-TPR). After being calcined at 800 ℃, 70%CeO2-30%ZrO2 exhibited the highest soot combustion activity, such that the maximum product concentration temperature (Tm) was decreased from 719 to 625 ℃ when employing this catalyst. The 70%CeO2-30%ZrO2 also showed excellent thermal stability, indicating that this could be an appropriate catalyst for soot combustion in gasoline direct injection engines. The differences in the soot combustion activities of the catalysts were closely related to their structures, surface compositions, and redox properties. XRD and Raman data demonstrated that the ceriumrich samples presented a typical cubic phase, while a tetragonal phase was observed in the case of the zirconium-rich samples. XPS showed that the molar fraction of Ce3+ in total Ce and the molar fraction of surfaceadsorbed oxygen to lattice oxygen on the surfaces of various samples differed, and these variations induced their different catalytic activities. The 70%CeO2-30%ZrO2 sample showed the largest OSC value and the most pronounced reduction properties. This same material was also found to have excellent thermal stability with regard to structure, surface composition, and redox properties, as reflected in the minimal degradation of the soot combustion activity of this catalyst with increasing calcination temperature.
2016, 32(7): 1758-1764
doi: 10.3866/PKU.WHXB2016032805
Abstract:
Rutile is much less active than anatase and brookite for the photocatalytic degradation of organic pollutants in aqueous solution. In this work, we found that addition of a trace amount of CuWO4 greatly accelerated phenol degradation in an aerated aqueous suspension of rutile. The increased rate was not only much higher than those of anatase and brookite, prepared at the same temperature (600 ℃), but also increased continuously with the sintering temperature of rutile from 150 to 800 ℃. These observations indicate that the high intrinsic photocatalytic activity of rutile produced at a high sintering temperature can be exploited by using co-catalyst CuWO4. Furthermore, as the amount of CuWO4 added to the suspension increased, the amount of H2O2 produced in the presence of excess phenol increased and then decreased; the trend was similar to that observed for phenol degradation. The observed positive effect of CuWO4 is mainly caused by solid CuWO4 rather than Cu2+ ions in aqueous solution. A (photo)electrochemical measurement showed that interfacial electron transfer occurred from the irradiated rutile to CuWO4. This would improve the charge-separation efficiency, and consequently increase the rates of O2 reduction and phenol degradation.
Rutile is much less active than anatase and brookite for the photocatalytic degradation of organic pollutants in aqueous solution. In this work, we found that addition of a trace amount of CuWO4 greatly accelerated phenol degradation in an aerated aqueous suspension of rutile. The increased rate was not only much higher than those of anatase and brookite, prepared at the same temperature (600 ℃), but also increased continuously with the sintering temperature of rutile from 150 to 800 ℃. These observations indicate that the high intrinsic photocatalytic activity of rutile produced at a high sintering temperature can be exploited by using co-catalyst CuWO4. Furthermore, as the amount of CuWO4 added to the suspension increased, the amount of H2O2 produced in the presence of excess phenol increased and then decreased; the trend was similar to that observed for phenol degradation. The observed positive effect of CuWO4 is mainly caused by solid CuWO4 rather than Cu2+ ions in aqueous solution. A (photo)electrochemical measurement showed that interfacial electron transfer occurred from the irradiated rutile to CuWO4. This would improve the charge-separation efficiency, and consequently increase the rates of O2 reduction and phenol degradation.
2016, 32(7): 1765-1774
doi: 10.3866/PKU.WHXB201604085
Abstract:
The supported Ru catalysts were prepared by the impregnation-chemical reduction method to investigate the effect of some conventional oxide supports (SiO2, m-ZrO2, t-ZrO2, γ-Al2O3, and P25) on the partial hydrogenation of toluene to methylcyclohexenes. The catalysts were characterized by N2 physisorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the supports influenced the size of the Ru nanoparticles (NPs) and consequently the catalytic performance. With the increase in the size of the Ru NPs from 2.6 to 17.3 nm, the turnover frequency (TOF) of toluene and the initial selectivity (S0) to methylcyclohexenes increased first, reached the maximum, and then decreased, following a volcano-like curve. At the Ru particle size of 3.0 nm, both TOF and S0 reached the highest values. Reaction conditions, such as the type and concentration of the modifiers, the temperature, and the pressure, were optimized over the best Ru/P25 catalyst among the supported Ru catalysts investigated herein. Under the reaction conditions of 423 K, H2 pressure of 5.0 MPa, and using 0.25 g zinc sulfate heptahydrate as the modifier, the initial hydrogenation activity (r0) of 26 mmol·g-1·min-1, the S0 of 57%, and the methylcyclohexenes yield of 36% were obtained.
The supported Ru catalysts were prepared by the impregnation-chemical reduction method to investigate the effect of some conventional oxide supports (SiO2, m-ZrO2, t-ZrO2, γ-Al2O3, and P25) on the partial hydrogenation of toluene to methylcyclohexenes. The catalysts were characterized by N2 physisorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the supports influenced the size of the Ru nanoparticles (NPs) and consequently the catalytic performance. With the increase in the size of the Ru NPs from 2.6 to 17.3 nm, the turnover frequency (TOF) of toluene and the initial selectivity (S0) to methylcyclohexenes increased first, reached the maximum, and then decreased, following a volcano-like curve. At the Ru particle size of 3.0 nm, both TOF and S0 reached the highest values. Reaction conditions, such as the type and concentration of the modifiers, the temperature, and the pressure, were optimized over the best Ru/P25 catalyst among the supported Ru catalysts investigated herein. Under the reaction conditions of 423 K, H2 pressure of 5.0 MPa, and using 0.25 g zinc sulfate heptahydrate as the modifier, the initial hydrogenation activity (r0) of 26 mmol·g-1·min-1, the S0 of 57%, and the methylcyclohexenes yield of 36% were obtained.
2016, 32(7): 1775-1784
doi: 10.3866/PKU.WHXB201604141
Abstract:
The hydrothermal synthesis method is used to prepare various crystal sizes of ZSM-5, and the effect of the crystal size on the alkylation of benzene with methanol is systematically investigated. The research results show that the conversion of benzene, selectivity of xylene, and the stability of the catalyst all decrease significantly with increasing crystal size. The ZSM-5 zeolite with a crystal size of 0.25 μm possesses the best catalytic performance and stability compared with other larger-sized zeolites. In addition, the deposition species and deactivation mechanism were also studied by Raman spectroscopy and thermogravimetric analysis. The results indicate that the catalyst deactivation may be attributed to the formation of polycyclic aromatic molecules, which can block the channel of the zeolite and cover the active sites. Finally, the effects of the reaction temperature, ratio of benzene to methanol, and space velocity on the alkylation of benzene with methanol are also investigated, and the optimum reaction conditions are determined.
The hydrothermal synthesis method is used to prepare various crystal sizes of ZSM-5, and the effect of the crystal size on the alkylation of benzene with methanol is systematically investigated. The research results show that the conversion of benzene, selectivity of xylene, and the stability of the catalyst all decrease significantly with increasing crystal size. The ZSM-5 zeolite with a crystal size of 0.25 μm possesses the best catalytic performance and stability compared with other larger-sized zeolites. In addition, the deposition species and deactivation mechanism were also studied by Raman spectroscopy and thermogravimetric analysis. The results indicate that the catalyst deactivation may be attributed to the formation of polycyclic aromatic molecules, which can block the channel of the zeolite and cover the active sites. Finally, the effects of the reaction temperature, ratio of benzene to methanol, and space velocity on the alkylation of benzene with methanol are also investigated, and the optimum reaction conditions are determined.
2016, 32(7): 1785-1794
doi: 10.3866/PKU.WHXB201604152
Abstract:
The cause of the deactivation of a methanol-to-propylene (MTP) catalyst after multiple reaction cycles was studied. On this basis, a facile and effective approach, i.e., secondary crystallization, was proposed and applied to the regeneration of the catalyst. The HZSM-5 zeolite catalysts before and after regeneration were characterized by a series of techniques, including powder X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), N2 adsorption, 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR), temperature-programmed desorption of ammonia (NH3-TPD), and infrared spectroscopy of adsorbed pyridine (Py-IR). The physicochemical properties, such as framework, silica/alumina ratio, texture, and acidity, of the deactivated catalysts and the regenerated ones were investigated in detail. The catalytic performance of the zeolites in MTP conversion was tested under operating conditions of T = 470 ℃, p = 0.1 MPa (pMeOH = 30 kPa) and weight hourly space velocity (WHSV) = 1 h-1. The collapse of the zeolite structure and loss of active sites were found to be the essential reasons for the decline in catalyst activity after multiple reaction cycles. By regeneration via secondary crystallization, the relative crystallization, specific surface area, pore volume and acidity of the HZSM-5 catalyst were increased prominently. Meanwhile, the destroyed crystal structure and acid sites of the deactivated catalyst were restored effectively. Thus, the regenerated catalyst again exhibited excellent methanol conversion capacity and propylene selectivity in the MTP reaction.
The cause of the deactivation of a methanol-to-propylene (MTP) catalyst after multiple reaction cycles was studied. On this basis, a facile and effective approach, i.e., secondary crystallization, was proposed and applied to the regeneration of the catalyst. The HZSM-5 zeolite catalysts before and after regeneration were characterized by a series of techniques, including powder X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), N2 adsorption, 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR), temperature-programmed desorption of ammonia (NH3-TPD), and infrared spectroscopy of adsorbed pyridine (Py-IR). The physicochemical properties, such as framework, silica/alumina ratio, texture, and acidity, of the deactivated catalysts and the regenerated ones were investigated in detail. The catalytic performance of the zeolites in MTP conversion was tested under operating conditions of T = 470 ℃, p = 0.1 MPa (pMeOH = 30 kPa) and weight hourly space velocity (WHSV) = 1 h-1. The collapse of the zeolite structure and loss of active sites were found to be the essential reasons for the decline in catalyst activity after multiple reaction cycles. By regeneration via secondary crystallization, the relative crystallization, specific surface area, pore volume and acidity of the HZSM-5 catalyst were increased prominently. Meanwhile, the destroyed crystal structure and acid sites of the deactivated catalyst were restored effectively. Thus, the regenerated catalyst again exhibited excellent methanol conversion capacity and propylene selectivity in the MTP reaction.
2016, 32(7): 1795-1800
doi: 10.3866/PKU.WHXB201606021
Abstract:
Volatile organic compounds (VOCs) such as toluene in the atmosphere are known to be potentially harmful to the environment and to human health, and catalytic combustion is one of the effective methods to remove the VOCs. In this work, rod-like copper-manganese mixed oxides with high specific areas were produced from copper-manganese mixed oxide particles by hydrothermal treatment with sodium hydroxide. The catalytic activity and deactivation of toluene combustion on these materials were subsequently studied. It was found that the catalytic combustion activity was greatly affected by the calcination temperature of the oxide. A sample calcined at 500 ℃ with a Brunauer-Emmett-Teller (BET) surface area of 221 m2·g-1 exhibited an activity very close to that of noble metal catalysts, enabling the complete catalytic combustion of toluene at 210 ℃. After running at 250 ℃ for 60 h, the toluene conversion droped from an initial value of 100% to 83%. X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2-TPR) showed that the relative proportions of Mn4+ and Mn3+ in the used catalyst decreased from 40.4% and 55.0% to 29.9% and 50.0%, respectively, while the relative proportion of Mn2+ increased from 4.60% to 20.6%. In addition, the amount of surface-adsorbed oxygen decreased from 34.8% to 29.2%, indicating that the catalytic activity is closely related with surface-adsorbed oxygen and high-valance Mn species. The H2-TPR peaks associated with copper oxide and manganese oxide transitioned from 248 and 311 ℃ to 268 and 333 ℃, respectively, illustrating that the deactivation resulted from a loss of redox properties. These results will be useful in further developing highly efficient, stable materials for the catalytic removal of VOCs in the atmosphere.
Volatile organic compounds (VOCs) such as toluene in the atmosphere are known to be potentially harmful to the environment and to human health, and catalytic combustion is one of the effective methods to remove the VOCs. In this work, rod-like copper-manganese mixed oxides with high specific areas were produced from copper-manganese mixed oxide particles by hydrothermal treatment with sodium hydroxide. The catalytic activity and deactivation of toluene combustion on these materials were subsequently studied. It was found that the catalytic combustion activity was greatly affected by the calcination temperature of the oxide. A sample calcined at 500 ℃ with a Brunauer-Emmett-Teller (BET) surface area of 221 m2·g-1 exhibited an activity very close to that of noble metal catalysts, enabling the complete catalytic combustion of toluene at 210 ℃. After running at 250 ℃ for 60 h, the toluene conversion droped from an initial value of 100% to 83%. X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2-TPR) showed that the relative proportions of Mn4+ and Mn3+ in the used catalyst decreased from 40.4% and 55.0% to 29.9% and 50.0%, respectively, while the relative proportion of Mn2+ increased from 4.60% to 20.6%. In addition, the amount of surface-adsorbed oxygen decreased from 34.8% to 29.2%, indicating that the catalytic activity is closely related with surface-adsorbed oxygen and high-valance Mn species. The H2-TPR peaks associated with copper oxide and manganese oxide transitioned from 248 and 311 ℃ to 268 and 333 ℃, respectively, illustrating that the deactivation resulted from a loss of redox properties. These results will be useful in further developing highly efficient, stable materials for the catalytic removal of VOCs in the atmosphere.
2016, 32(7): 1801-1809
doi: 10.3866/PKU.WHXB201604081
Abstract:
PdO/PdO/Ce1-xPdxO2-δ (PdO/CP) and PdO/Ce1-x-yPdxZryO2-δ (PdO/CPZ) catalysts were prepared via a solution combustion method. The corresponding PdO/Ce1-xPdxO2-δ (CP) and Ce1-x-yPdxZryO2-δ (CPZ) catalysts were obtained by nitric acid treatment of the PdO/CP and PdO/CPZ catalysts to remove the surface PdO species. These catalysts were tested for CO and CH4 catalytic oxidation. The turnover frequencies (TOFs) of surface PdO and Pdn+ cations in the CP and CPZ solid solutions were calculated. The results showed that Zr addition in the PdO/CP catalyst had very different effects on CO and CH4 oxidation. A significant improvement in CO oxidation activity was observed over the Zr-containing catalysts; this could be related to the formation of smaller PdO particles on the surface of the PdO/CPZ catalyst and a higher oxygen vacancy concentration in the CPZ solid solution. For CH4 oxidation, Pdn + cations in the solid solution play a key role in the catalytic oxidation process. The penetration of Zr4+ cations into the CeO2 lattice decreased the amount of Pd2+ cations in the CPZ solid solution and thus inhibited the activities of the Zr-containing catalysts (PdO/CPZ and CPZ) for CH4 oxidation.
PdO/PdO/Ce1-xPdxO2-δ (PdO/CP) and PdO/Ce1-x-yPdxZryO2-δ (PdO/CPZ) catalysts were prepared via a solution combustion method. The corresponding PdO/Ce1-xPdxO2-δ (CP) and Ce1-x-yPdxZryO2-δ (CPZ) catalysts were obtained by nitric acid treatment of the PdO/CP and PdO/CPZ catalysts to remove the surface PdO species. These catalysts were tested for CO and CH4 catalytic oxidation. The turnover frequencies (TOFs) of surface PdO and Pdn+ cations in the CP and CPZ solid solutions were calculated. The results showed that Zr addition in the PdO/CP catalyst had very different effects on CO and CH4 oxidation. A significant improvement in CO oxidation activity was observed over the Zr-containing catalysts; this could be related to the formation of smaller PdO particles on the surface of the PdO/CPZ catalyst and a higher oxygen vacancy concentration in the CPZ solid solution. For CH4 oxidation, Pdn + cations in the solid solution play a key role in the catalytic oxidation process. The penetration of Zr4+ cations into the CeO2 lattice decreased the amount of Pd2+ cations in the CPZ solid solution and thus inhibited the activities of the Zr-containing catalysts (PdO/CPZ and CPZ) for CH4 oxidation.
2016, 32(7): 1810-1818
doi: 10.3866/PKU.WHXB201604145
Abstract:
Interactions of peroxovanadiumcomplexes (NH4)[VO(O2)2(bipy)]·4H2O (1) and (NH4)[VO(O2)2(phen)]· 2H2O (2) with the mutant peptide M109F of prion neuropeptide PrP106-126 have been investigated by fluorescence spectroscopy (FS), nuclear magnetic resonance (NMR), electron spray ionization mass spectrometry (ESI-MS) and transmission electron microscopy (TEM) methods. The results show that the peroxovanadium complexes may directly bind to the M109F peptide, and react with the peptide by methionine oxidation at Met112, resulting in the inhibition of M109F peptide aggregation. Compared with complex 2, complex 1 shows improved inhibitory effects on peptide M109F. Both complexes 1 and 2 exhibit an increased cellular viability against amyloid peptide-induced cytotoxicity. The basic data for the investigation of potential metallodrugs against neurodegenerative disease are provided.
Interactions of peroxovanadiumcomplexes (NH4)[VO(O2)2(bipy)]·4H2O (1) and (NH4)[VO(O2)2(phen)]· 2H2O (2) with the mutant peptide M109F of prion neuropeptide PrP106-126 have been investigated by fluorescence spectroscopy (FS), nuclear magnetic resonance (NMR), electron spray ionization mass spectrometry (ESI-MS) and transmission electron microscopy (TEM) methods. The results show that the peroxovanadium complexes may directly bind to the M109F peptide, and react with the peptide by methionine oxidation at Met112, resulting in the inhibition of M109F peptide aggregation. Compared with complex 2, complex 1 shows improved inhibitory effects on peptide M109F. Both complexes 1 and 2 exhibit an increased cellular viability against amyloid peptide-induced cytotoxicity. The basic data for the investigation of potential metallodrugs against neurodegenerative disease are provided.
2016, 32(7): 1819-1828
doi: 10.3866/PKU.WHXB201604151
Abstract:
Human serum albumin (HSA) is an extracellular protein that has the highest concentration in blood plasma and is a carrier for many small molecules. HSA has an exceptional binding capacity for many endogenous and exogenous ligands, and contains two main binding sites with high affinity for diverse substances, named Site I and Site II. The binding cavity of Site II is more active and has greater ligand affinity than that of Site I. In this study, molecular simulation methods were used to investigate the molecular interactions between Site II and twelve Site II-specific ligands. The results showed that hydrophobic interactions were the main driving force for binding, with electrostatic interactions playing a secondary role. The key residues and binding mode on Site II were identified with the computational alanine-scanning approach. Three layers were found from the entrance to the interior of the binding pocket, contributing electrostatic interactions, hydrophobic interactions and mixed interactions, respectively. Finally, molecular docking and molecular dynamics were used to predict the binding mode of L-tryptophan on Site II. The results provided insights into the binding mode of Site II on HSA, which could guide the design of new Site II-specific drugs and ligands for the efficient separation of HSA.
Human serum albumin (HSA) is an extracellular protein that has the highest concentration in blood plasma and is a carrier for many small molecules. HSA has an exceptional binding capacity for many endogenous and exogenous ligands, and contains two main binding sites with high affinity for diverse substances, named Site I and Site II. The binding cavity of Site II is more active and has greater ligand affinity than that of Site I. In this study, molecular simulation methods were used to investigate the molecular interactions between Site II and twelve Site II-specific ligands. The results showed that hydrophobic interactions were the main driving force for binding, with electrostatic interactions playing a secondary role. The key residues and binding mode on Site II were identified with the computational alanine-scanning approach. Three layers were found from the entrance to the interior of the binding pocket, contributing electrostatic interactions, hydrophobic interactions and mixed interactions, respectively. Finally, molecular docking and molecular dynamics were used to predict the binding mode of L-tryptophan on Site II. The results provided insights into the binding mode of Site II on HSA, which could guide the design of new Site II-specific drugs and ligands for the efficient separation of HSA.
2016, 32(7): 1829-1838
doi: 10.3866/PKU.WHXB201605191
Abstract:
Two series of (Fe0.81Ga0.19)100-xBx (Fe-Ga-B) and (Fe0.81Ga0.19)100-xInx (Fe-Ga-In) ribbons were successfully prepared with melt spinning method. Thermal treatments were afterwards conducted out on these Fe-Ga-B ribbons. The sample microstructures of the alloys were examined by high resolution X-ray diffraction (HRXRD) and extended X-ray absorption fine structure (EXAFS). The magnetic properties were measured by a vibrating sample magnetometer (VSM) at room temperature. The magnetostriction constant, measured by resistance strain gauge method, of the melt-spun (Fe0.81Ga0.19)98B2 ribbon decreased sharply due to the L12 phase. Both the Fe2B and modified-DO3 phases played a positive role in increasing the magnetostriction constant of the Fe-Ga alloys. The Fe2B phase presented a lower saturation magnetization and a larger saturation field. As the B composition increased, the saturation magnetization of the ribbons decreased and the coercivity intensified. For the Fe-Ga-In ribbons, the non-magnetic In-rich phase was formed, leading to their lattices distortion and, hence, the magnetoelastic effect was weakened. The non-magnetic In-rich phase could suppress the movements of the magnetic domain and domain wall. Therefore, In-doping decreased the saturation magnetostriction and saturation magnetization of the Fe-Ga alloy. In-doping could also increase the coercivity of the Fe-Ga alloy. The addition of B and In changed the microstructures of the Fe-Ga alloys and accordingly their magnetic properties and magnetostriction.
Two series of (Fe0.81Ga0.19)100-xBx (Fe-Ga-B) and (Fe0.81Ga0.19)100-xInx (Fe-Ga-In) ribbons were successfully prepared with melt spinning method. Thermal treatments were afterwards conducted out on these Fe-Ga-B ribbons. The sample microstructures of the alloys were examined by high resolution X-ray diffraction (HRXRD) and extended X-ray absorption fine structure (EXAFS). The magnetic properties were measured by a vibrating sample magnetometer (VSM) at room temperature. The magnetostriction constant, measured by resistance strain gauge method, of the melt-spun (Fe0.81Ga0.19)98B2 ribbon decreased sharply due to the L12 phase. Both the Fe2B and modified-DO3 phases played a positive role in increasing the magnetostriction constant of the Fe-Ga alloys. The Fe2B phase presented a lower saturation magnetization and a larger saturation field. As the B composition increased, the saturation magnetization of the ribbons decreased and the coercivity intensified. For the Fe-Ga-In ribbons, the non-magnetic In-rich phase was formed, leading to their lattices distortion and, hence, the magnetoelastic effect was weakened. The non-magnetic In-rich phase could suppress the movements of the magnetic domain and domain wall. Therefore, In-doping decreased the saturation magnetostriction and saturation magnetization of the Fe-Ga alloy. In-doping could also increase the coercivity of the Fe-Ga alloy. The addition of B and In changed the microstructures of the Fe-Ga alloys and accordingly their magnetic properties and magnetostriction.
2016, 32(7): 1839-1843
doi: 10.3866/PKU.WHXB201604063
Abstract:
Graphene-doped diamond-like carbon(G/a-C:H) nanocomposite films were fabricated using a liquidphase electrochemical method. A nanocomposite film growth mechanism is proposed and discussed. The deposited films were characterized using scanning electron microscopy (SEM), Raman spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The results showed that graphene sheets were homogeneously dispersed in a hydrogenated amorphous carbon (a-C:H) matrix. The deposited G/a-C:H film surface was uniform and smooth. Field emission experiments showed that graphene doping slightly increased the turn-on field, from 4.7 to 5.8 V·μm-1, and significantly improved the current density, from 384 to 876 μA·cm-2.
Graphene-doped diamond-like carbon(G/a-C:H) nanocomposite films were fabricated using a liquidphase electrochemical method. A nanocomposite film growth mechanism is proposed and discussed. The deposited films were characterized using scanning electron microscopy (SEM), Raman spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The results showed that graphene sheets were homogeneously dispersed in a hydrogenated amorphous carbon (a-C:H) matrix. The deposited G/a-C:H film surface was uniform and smooth. Field emission experiments showed that graphene doping slightly increased the turn-on field, from 4.7 to 5.8 V·μm-1, and significantly improved the current density, from 384 to 876 μA·cm-2.
2016, 32(7): 1844-1850
doi: 10.3866/PKU.WHXB201604142
Abstract:
BiOBr/Bi2WO6 with squamous morphology is successfully prepared by a one-step hydrothermal method. BiOBr/Bi2WO6 is shown to be an ideal material for adsorption. The structure of BiOBr/Bi2WO6 is characterized by powder X-ray diffraction (XRD), X-ray photoelectron (XPS) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, and the morphology is observed with scanning electron microscopy (SEM). The specific surface of BiOBr/Bi2WO6 is tested by a nitrogen adsorption/desorption surface area pore size distribution analyzer. According to the experiments with different concentrations of KBr and the SEM photos of BiOBr and Bi2WO6, the possible morphology formation mechanism of squamous BiOBr/Bi2WO6 is proposed. We design a series of adsorption experiments and test the adsorption properties of the compounds with organic dyes as adsorbent and BiOBr/Bi2WO6 as adsorbent. The results show that BiOBr/Bi2WO6 exhibits a higher adsorption capacity for cationic dyes, especially the adsorption rate of MB, and BiOBr/Bi2WO6 shows a higher adsorption capacity compared with that of activated carbon. Adsorption behavior of BiOBr/Bi2WO6 is consistent with the Freundlich isotherm model and the adsorption process of MB follows a pseudo-second-order kinetic model.
BiOBr/Bi2WO6 with squamous morphology is successfully prepared by a one-step hydrothermal method. BiOBr/Bi2WO6 is shown to be an ideal material for adsorption. The structure of BiOBr/Bi2WO6 is characterized by powder X-ray diffraction (XRD), X-ray photoelectron (XPS) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, and the morphology is observed with scanning electron microscopy (SEM). The specific surface of BiOBr/Bi2WO6 is tested by a nitrogen adsorption/desorption surface area pore size distribution analyzer. According to the experiments with different concentrations of KBr and the SEM photos of BiOBr and Bi2WO6, the possible morphology formation mechanism of squamous BiOBr/Bi2WO6 is proposed. We design a series of adsorption experiments and test the adsorption properties of the compounds with organic dyes as adsorbent and BiOBr/Bi2WO6 as adsorbent. The results show that BiOBr/Bi2WO6 exhibits a higher adsorption capacity for cationic dyes, especially the adsorption rate of MB, and BiOBr/Bi2WO6 shows a higher adsorption capacity compared with that of activated carbon. Adsorption behavior of BiOBr/Bi2WO6 is consistent with the Freundlich isotherm model and the adsorption process of MB follows a pseudo-second-order kinetic model.
