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2018 Volume 39 Issue 9
2018, 39(9):
Abstract:
2018, 39(9): 1437-1444
doi: 10.1016/S1872-2067(18)63065-7
Abstract:
As an emerging class of crystalline porous materials, covalent organic frameworks (COFs) have been widely used as catalysts or catalyst supports. Flexible regulation of the pores and easy introduction of functional active sites onto the skeleton of COFs make them promising platforms for many catalysis applications. However, only a single function is generally observed in these COFs. Herein, we synthesized a negatively charged ionic COF (I-COF) and successfully incorporated functionalized counter ions, that is, metallic Mn2+ and a coordination complex of manganese(Ⅱ) bipyridine complexes ([Mn(bpy)2]2+), via a simple ion exchange process. The resulting I-COFs can act as effective heterogeneous catalysts for epoxidation reactions. We envisage that with this type of ionic architecture, a variety of other functional cations could be exchanged into the frameworks, thus making the COF a versatile platform for different applications.
As an emerging class of crystalline porous materials, covalent organic frameworks (COFs) have been widely used as catalysts or catalyst supports. Flexible regulation of the pores and easy introduction of functional active sites onto the skeleton of COFs make them promising platforms for many catalysis applications. However, only a single function is generally observed in these COFs. Herein, we synthesized a negatively charged ionic COF (I-COF) and successfully incorporated functionalized counter ions, that is, metallic Mn2+ and a coordination complex of manganese(Ⅱ) bipyridine complexes ([Mn(bpy)2]2+), via a simple ion exchange process. The resulting I-COFs can act as effective heterogeneous catalysts for epoxidation reactions. We envisage that with this type of ionic architecture, a variety of other functional cations could be exchanged into the frameworks, thus making the COF a versatile platform for different applications.
2018, 39(9): 1445-1452
doi: 10.1016/S1872-2067(18)63132-8
Abstract:
Transformation of lignin into high-value chemicals is hampered by the complexity of monomers obtained from lignin depolymerization. Here we report a strategy, composed of hydro-demethoxylation and de-alkylation reactions, that is able to chemically converge various lignin-derived phenolic monomers into phenol in a single-step. Using 2-methoxy-4-propylphenol as a model compound, Pt/C exhibited the best performance in hydro-demethoxylation reaction affording >80% 4-propylphenol from 2-methoxy-4-propylphenol, while H-ZSM-5 was identified as the most suitable catalyst for de-alkylation, achieving 83% yield of phenol from 4-propylphenol. Since the two catalysts operate under compatible conditions, combining the two catalysts to simultaneously promote both hydro-demethoxylation and de-alkylation reactions was achieved. Configuration of how to organize the catalysts is a critical parameter, where the physical mixture of the two was most effective, providing over 60% phenol from 2-methoxy-4-propylphenol in a single-step.
Transformation of lignin into high-value chemicals is hampered by the complexity of monomers obtained from lignin depolymerization. Here we report a strategy, composed of hydro-demethoxylation and de-alkylation reactions, that is able to chemically converge various lignin-derived phenolic monomers into phenol in a single-step. Using 2-methoxy-4-propylphenol as a model compound, Pt/C exhibited the best performance in hydro-demethoxylation reaction affording >80% 4-propylphenol from 2-methoxy-4-propylphenol, while H-ZSM-5 was identified as the most suitable catalyst for de-alkylation, achieving 83% yield of phenol from 4-propylphenol. Since the two catalysts operate under compatible conditions, combining the two catalysts to simultaneously promote both hydro-demethoxylation and de-alkylation reactions was achieved. Configuration of how to organize the catalysts is a critical parameter, where the physical mixture of the two was most effective, providing over 60% phenol from 2-methoxy-4-propylphenol in a single-step.
2018, 39(9): 1453-1462
doi: 10.1016/S1872-2067(18)63124-9
Abstract:
Doping heteroatoms into carbon matrix was an efficient strategy to achieve a high-performance non-precious metal oxygen reduction electrocatalyst. Herein, an in situ templated synthesis strategy has been demonstrated to fabricate nitrogen, sulfur and iron-tridoped mesoporous carbon nanosheets (NSFC) with FeCl3 as the two-dimensional template. And a protic salt was used as the carbon, nitrogen and sulfur source, which realized one-step preparation of catalyst materials and the co-doping of various heteroatoms simultaneously. As a result, the optimized NSFC catalyst possessed comparable catalytic activity and selectivity, while superior durability and methanol permeability resistance to commercial 30 wt% Pt/C catalyst in alkaline media. Such excellent performance should be ascribed to the efficient multiple-element doping into the large-specific-surface-area and highly stable carbon nanosheets realized by the in situ synthesis route with a novel FeCl3 template.
Doping heteroatoms into carbon matrix was an efficient strategy to achieve a high-performance non-precious metal oxygen reduction electrocatalyst. Herein, an in situ templated synthesis strategy has been demonstrated to fabricate nitrogen, sulfur and iron-tridoped mesoporous carbon nanosheets (NSFC) with FeCl3 as the two-dimensional template. And a protic salt was used as the carbon, nitrogen and sulfur source, which realized one-step preparation of catalyst materials and the co-doping of various heteroatoms simultaneously. As a result, the optimized NSFC catalyst possessed comparable catalytic activity and selectivity, while superior durability and methanol permeability resistance to commercial 30 wt% Pt/C catalyst in alkaline media. Such excellent performance should be ascribed to the efficient multiple-element doping into the large-specific-surface-area and highly stable carbon nanosheets realized by the in situ synthesis route with a novel FeCl3 template.
2018, 39(9): 1463-1469
doi: 10.1016/S1872-2067(18)63116-X
Abstract:
Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv. 2,2-dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins including styrenes, chromenes, and cinnamamides were transformed successfully into the target epoxides with moderate to excellent enantioselectivity (yield up to 95%, ee up to 99%).
Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv. 2,2-dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins including styrenes, chromenes, and cinnamamides were transformed successfully into the target epoxides with moderate to excellent enantioselectivity (yield up to 95%, ee up to 99%).
2018, 39(9): 1470-1483
doi: 10.1016/S1872-2067(18)63111-0
Abstract:
In this work, an efficient AgVO3/MoS2 composite photocatalyst was successfully synthesized via a hydrothermal method. The photocatalytic activity of the as-prepared photocatalyst was evaluated by using it for assessing the degradation of different organic pollutants under visible-light irradiation. The composite 3%-AgVO3/MoS2 catalyst demonstrated a significantly enhanced photocatalytic activity compared to the pure compounds (AgVO3 and MoS2). The reason behind the excellent photocatalytic performance was the modification of MoS2 by AgVO3 to facilitate O2 adsorption/activation. In addition, the composite catalyst facilitates the two-electron oxygen reduction reaction whereby H2O2 is generated on the surface of MoS2 to produce additional reactive oxygen species (ROSs). ESR coupled with the POPHA fluorescence detection method and a free radical capture experiment were used to elucidate the mechanism of formation of the ROSs, including ·OH, ·O2- and H2O2. Furthermore, the generation of additional ROSs could accelerate electron consumption, leaving behind more holes for the oxidation of organic pollutants. A possible photocatalytic mechanism of the composite is also discussed.
In this work, an efficient AgVO3/MoS2 composite photocatalyst was successfully synthesized via a hydrothermal method. The photocatalytic activity of the as-prepared photocatalyst was evaluated by using it for assessing the degradation of different organic pollutants under visible-light irradiation. The composite 3%-AgVO3/MoS2 catalyst demonstrated a significantly enhanced photocatalytic activity compared to the pure compounds (AgVO3 and MoS2). The reason behind the excellent photocatalytic performance was the modification of MoS2 by AgVO3 to facilitate O2 adsorption/activation. In addition, the composite catalyst facilitates the two-electron oxygen reduction reaction whereby H2O2 is generated on the surface of MoS2 to produce additional reactive oxygen species (ROSs). ESR coupled with the POPHA fluorescence detection method and a free radical capture experiment were used to elucidate the mechanism of formation of the ROSs, including ·OH, ·O2- and H2O2. Furthermore, the generation of additional ROSs could accelerate electron consumption, leaving behind more holes for the oxidation of organic pollutants. A possible photocatalytic mechanism of the composite is also discussed.
2018, 39(9): 1484-1492
doi: 10.1016/S1872-2067(18)63118-3
Abstract:
La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) anodes were infiltrated by Gd0.2Ce0.8O1.9 (GDC) nanoparticles to improve the oxygen evolution reaction (OER) performance of solid oxide electrolysis cells (SOECs) in CO2 electroreduction. The effect of GDC loading was investigated, and 10 wt% GDC nanoparticle infiltration of the LSCF (10GDC/LSCF) anode results in the highest OER performance. Electrochemical impedance spectra measurements indicate that the infiltration by GDC nanoparticles greatly decreases the polarization resistance of the SOECs with the 10GDC/LSCF anodes. The following distribution of relaxation time analysis suggests that four individual electrode processes are involved in the OER and that all of them are accelerated on the 10GDC/LSCF anode. Three phase boundaries, surface oxygen vacancies, and bulk oxygen mobility increased, based on scanning electron microscopy and temperature-programmed desorption of O2 characterizations, and contributed to the enhancement of the four electrode processes of the OER and electrochemical performance of SOECs.
La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) anodes were infiltrated by Gd0.2Ce0.8O1.9 (GDC) nanoparticles to improve the oxygen evolution reaction (OER) performance of solid oxide electrolysis cells (SOECs) in CO2 electroreduction. The effect of GDC loading was investigated, and 10 wt% GDC nanoparticle infiltration of the LSCF (10GDC/LSCF) anode results in the highest OER performance. Electrochemical impedance spectra measurements indicate that the infiltration by GDC nanoparticles greatly decreases the polarization resistance of the SOECs with the 10GDC/LSCF anodes. The following distribution of relaxation time analysis suggests that four individual electrode processes are involved in the OER and that all of them are accelerated on the 10GDC/LSCF anode. Three phase boundaries, surface oxygen vacancies, and bulk oxygen mobility increased, based on scanning electron microscopy and temperature-programmed desorption of O2 characterizations, and contributed to the enhancement of the four electrode processes of the OER and electrochemical performance of SOECs.
2018, 39(9): 1493-1499
doi: 10.1016/S1872-2067(18)63081-5
Abstract:
The effects of surface strain and subsurface promoters, which are both important factors in heterogeneous catalysis, on catalytic selectivity and activity of Pd are examined in this study by considering the selective hydrogenation of acetylene as an example. Combined density functional theory calculations and microkinetic modeling reveal that the selectivity and activity of the Pd catalyst for acetylene hydrogenation can both be substantially influenced by the effects of Pd lattice strain variation and subsurface carbon species formation on the adsorption properties of the reactants and products. It is found that the adsorption energies of the reactants and products are, in general, linearly scaled with the lattice strain for both pristine and subsurface carbon atom-modified Pd(111) surfaces, except for the adsorption of C2H2 over Pd(111)-C. The activity for ethylene formation typically corresponds to the region of strong reactants adsorption in the volcano curve; such an effect of lattice strain and the presence of subsurface promoters can improve the activity of the catalyst through the weakening of the adsorption of reactants. The activity and selectivity for Pd(111)-C are always higher than those for the pristine Pd(111) surfaces with respect to ethylene formation. Based on the results obtained, Pd-based catalysts with shrinking lattice constants are suggested as good candidates for the selective hydrogenation of acetylene. A similar approach can be used to facilitate the future design of novel heterogeneous catalysts.
The effects of surface strain and subsurface promoters, which are both important factors in heterogeneous catalysis, on catalytic selectivity and activity of Pd are examined in this study by considering the selective hydrogenation of acetylene as an example. Combined density functional theory calculations and microkinetic modeling reveal that the selectivity and activity of the Pd catalyst for acetylene hydrogenation can both be substantially influenced by the effects of Pd lattice strain variation and subsurface carbon species formation on the adsorption properties of the reactants and products. It is found that the adsorption energies of the reactants and products are, in general, linearly scaled with the lattice strain for both pristine and subsurface carbon atom-modified Pd(111) surfaces, except for the adsorption of C2H2 over Pd(111)-C. The activity for ethylene formation typically corresponds to the region of strong reactants adsorption in the volcano curve; such an effect of lattice strain and the presence of subsurface promoters can improve the activity of the catalyst through the weakening of the adsorption of reactants. The activity and selectivity for Pd(111)-C are always higher than those for the pristine Pd(111) surfaces with respect to ethylene formation. Based on the results obtained, Pd-based catalysts with shrinking lattice constants are suggested as good candidates for the selective hydrogenation of acetylene. A similar approach can be used to facilitate the future design of novel heterogeneous catalysts.
2018, 39(9): 1500-1510
doi: 10.1016/S1872-2067(18)63096-7
Abstract:
Heterojunction fabrication is one of the most effective strategies for enhancing the photocatalytic performance of semiconductor photocatalysts. Here, TiO2(B)/anatase nanowires with interfacial heterostructures were prepared through a three-step synthesis method, including hydrothermal treatment, H+ exchange, and annealing. The phase structures of the nanowires in the bulk and on the surface during the annealing process were monitored by XRD and UV-Raman spectroscopy, respectively. SEM and TEM results indicate that the TiO2(B) nanowires partially collapse and transform into anatase during the annealing process and the heterophase junction structure is formed simultaneously. On the basis of the phase structure together with morphology data, a phase-transformation mechanism was proposed. Photocatalytic activity was evaluated by hydrogen production and pollutant-degradation assays. The optimized structure of the photocatalyst contains 24% TiO2(B) in the bulk and 100% anatase on the surface. The charge-carrier behavior during the photocatalytic process was investigated by photocurrent, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) spectroscopy, which revealed that the heterophase-junction structure in the bulk was responsible for the highly efficient charge separation and transportation, etc.; the anatase on the surface took control of the high surface-reaction activity.
Heterojunction fabrication is one of the most effective strategies for enhancing the photocatalytic performance of semiconductor photocatalysts. Here, TiO2(B)/anatase nanowires with interfacial heterostructures were prepared through a three-step synthesis method, including hydrothermal treatment, H+ exchange, and annealing. The phase structures of the nanowires in the bulk and on the surface during the annealing process were monitored by XRD and UV-Raman spectroscopy, respectively. SEM and TEM results indicate that the TiO2(B) nanowires partially collapse and transform into anatase during the annealing process and the heterophase junction structure is formed simultaneously. On the basis of the phase structure together with morphology data, a phase-transformation mechanism was proposed. Photocatalytic activity was evaluated by hydrogen production and pollutant-degradation assays. The optimized structure of the photocatalyst contains 24% TiO2(B) in the bulk and 100% anatase on the surface. The charge-carrier behavior during the photocatalytic process was investigated by photocurrent, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) spectroscopy, which revealed that the heterophase-junction structure in the bulk was responsible for the highly efficient charge separation and transportation, etc.; the anatase on the surface took control of the high surface-reaction activity.
2018, 39(9): 1511-1519
doi: 10.1016/S1872-2067(18)63122-5
Abstract:
DNL-6, a silicoaluminophosphate (SAPO) molecular sieve with RHO topology, was hydrothermally synthesized using a new structure-directing agent (SDA), N,N'-dimethylethylenediamine. The obtained samples were characterized by X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption, which indicated that the synthesized DNL-6s have high crystallinity and relatively high Si content ranging from 20% to 35%. Solid-state magic-angle-spinning (MAS) nuclear magnetic resonance (13C, 29Si, 27Al, 31P, and 27Al multiple-quantum (MQ)) was conducted to investigate the status of the SDA and local atomic environment in the as-synthesized DNL-6. Thermal analysis revealed the presence of a large amount of amines in the DNL-6 crystals (about 4.4 SDAs per α-cage), which was the reason for the formation of DNL-6 with an ultrahigh Si content (36.4% Si per mole). Interestingly, DNL-6 exhibited excellent catalytic performance for methanol amination. More than 88% methanol conversion and 85% methylamine plus dimethylamine selectivity could be achieved due to the combined contribution of strong acid sites, suitable acid distribution, and narrow pore dimensions of DNL-6.
DNL-6, a silicoaluminophosphate (SAPO) molecular sieve with RHO topology, was hydrothermally synthesized using a new structure-directing agent (SDA), N,N'-dimethylethylenediamine. The obtained samples were characterized by X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption, which indicated that the synthesized DNL-6s have high crystallinity and relatively high Si content ranging from 20% to 35%. Solid-state magic-angle-spinning (MAS) nuclear magnetic resonance (13C, 29Si, 27Al, 31P, and 27Al multiple-quantum (MQ)) was conducted to investigate the status of the SDA and local atomic environment in the as-synthesized DNL-6. Thermal analysis revealed the presence of a large amount of amines in the DNL-6 crystals (about 4.4 SDAs per α-cage), which was the reason for the formation of DNL-6 with an ultrahigh Si content (36.4% Si per mole). Interestingly, DNL-6 exhibited excellent catalytic performance for methanol amination. More than 88% methanol conversion and 85% methylamine plus dimethylamine selectivity could be achieved due to the combined contribution of strong acid sites, suitable acid distribution, and narrow pore dimensions of DNL-6.
2018, 39(9): 1520-1526
doi: 10.1016/S1872-2067(18)63072-4
Abstract:
The oxidative dehydrogenation (ODH) of propane on monomeric VO3 supported by CeO2(111) (VO3/CeO2(111)) is studied by periodic density functional theory calculations. Detailed energetic, structural, and electronic properties of these reactions are determined. The calculated activation energies of the breaking of the first and second C-H bonds of propane on the VO3/CeO2(111) catalyst are compared, and it is found that both the unique structural and electronic effects of the VO3/CeO2(111) catalyst contribute to the relatively easy rupture of the first C-H bond of the propane molecule during the ODH reaction. In particular, the so-called new empty localized states that are mainly constituted of O 2p orbitals of the ceria-supported VO3 species are determined to be crucial for assisting the cleavage of the first C-H bond of the propane molecule. Following this they become occupied and the remaining C-H bonds become increasingly difficult to break owing to the increasing repulsion between the localized 4f electrons at the Ce cations, resulting in the adsorption of more H and other moieties. This work illustrates that CeO2-supported monomeric vanadium oxides can exhibit unique activity and selectivity for the catalytic ODH of alkanes to alkenes.
The oxidative dehydrogenation (ODH) of propane on monomeric VO3 supported by CeO2(111) (VO3/CeO2(111)) is studied by periodic density functional theory calculations. Detailed energetic, structural, and electronic properties of these reactions are determined. The calculated activation energies of the breaking of the first and second C-H bonds of propane on the VO3/CeO2(111) catalyst are compared, and it is found that both the unique structural and electronic effects of the VO3/CeO2(111) catalyst contribute to the relatively easy rupture of the first C-H bond of the propane molecule during the ODH reaction. In particular, the so-called new empty localized states that are mainly constituted of O 2p orbitals of the ceria-supported VO3 species are determined to be crucial for assisting the cleavage of the first C-H bond of the propane molecule. Following this they become occupied and the remaining C-H bonds become increasingly difficult to break owing to the increasing repulsion between the localized 4f electrons at the Ce cations, resulting in the adsorption of more H and other moieties. This work illustrates that CeO2-supported monomeric vanadium oxides can exhibit unique activity and selectivity for the catalytic ODH of alkanes to alkenes.
2018, 39(9): 1527-1533
doi: 10.1016/S1872-2067(18)63079-7
Abstract:
We report on a novel g-C3N4/TiO2/Co-Pi photoanode combining a TiO2 protection layer, Co-Pi hole capture layer, and g-C3N4 light-absorption layer layer for photoelectrochemical (PEC) water splitting to generate hydrogen for the first time. This new photoanode with three function layers exhibits enhanced PEC performance with a photocurrent density of 0.346 mA·cm-2 at 1.1 V (vs. RHE), which is approximately 3.6 times that of pure g-C3N4 photoanode. The enhanced PEC performance of g-C3N4/TiO2/Co-Pi photoanode benefits from the following:(1) excellent visible light absorption of g-C3N4; (2) stable protection of TiO2 to improve the durability of g-C3N4film; and (3)photogenerated holes capture Co-Pi to separate photogenerated electron-hole pairs efficiently. This promising multifarious function layers structure provides a new perspective for PEC water splitting to generate hydrogen.
We report on a novel g-C3N4/TiO2/Co-Pi photoanode combining a TiO2 protection layer, Co-Pi hole capture layer, and g-C3N4 light-absorption layer layer for photoelectrochemical (PEC) water splitting to generate hydrogen for the first time. This new photoanode with three function layers exhibits enhanced PEC performance with a photocurrent density of 0.346 mA·cm-2 at 1.1 V (vs. RHE), which is approximately 3.6 times that of pure g-C3N4 photoanode. The enhanced PEC performance of g-C3N4/TiO2/Co-Pi photoanode benefits from the following:(1) excellent visible light absorption of g-C3N4; (2) stable protection of TiO2 to improve the durability of g-C3N4film; and (3)photogenerated holes capture Co-Pi to separate photogenerated electron-hole pairs efficiently. This promising multifarious function layers structure provides a new perspective for PEC water splitting to generate hydrogen.
2018, 39(9): 1534-1542
doi: 10.1016/S1872-2067(18)63082-7
Abstract:
Several catalysts comprising Pt supported on octahedral Fe3O4 (Pt/Fe3O4) were prepared by a facile method involving co-precipitation followed by thermal treatment at different temperatures. A variety of characterization results revealed that this preparation process afforded highly crystalline octahedral Fe3O4 with a uniform distribution of Pt nanoparticles on its surface. The thermal-treatment temperature significantly influenced the redox properties of the Pt/Fe3O4 catalysts. All the Pt/Fe3O4 catalysts were found to be catalytically active and stable for the oxidation of low-concentration formaldehyde (HCHO) with oxygen. The catalyst prepared by thermal treatment at 80℃ (labelled Pt/Fe3O4-80) exhibited the highest catalytic activity, efficiently converting HCHO to CO2 and H2O under ambient temperature and moisture conditions. The excellent performance of Pt/Fe3O4-80 was mainly attributed to beneficial interactions between the Pt and Fe species that result in the formation a higher density of active interface sites (e.g., Pt-O-FeOx and Pt-OH-FeOx). The introduction of water vapor improves the catalytic activity of the Pt/Fe3O4 catalysts as it participates in a water-assisted dissociation process.
Several catalysts comprising Pt supported on octahedral Fe3O4 (Pt/Fe3O4) were prepared by a facile method involving co-precipitation followed by thermal treatment at different temperatures. A variety of characterization results revealed that this preparation process afforded highly crystalline octahedral Fe3O4 with a uniform distribution of Pt nanoparticles on its surface. The thermal-treatment temperature significantly influenced the redox properties of the Pt/Fe3O4 catalysts. All the Pt/Fe3O4 catalysts were found to be catalytically active and stable for the oxidation of low-concentration formaldehyde (HCHO) with oxygen. The catalyst prepared by thermal treatment at 80℃ (labelled Pt/Fe3O4-80) exhibited the highest catalytic activity, efficiently converting HCHO to CO2 and H2O under ambient temperature and moisture conditions. The excellent performance of Pt/Fe3O4-80 was mainly attributed to beneficial interactions between the Pt and Fe species that result in the formation a higher density of active interface sites (e.g., Pt-O-FeOx and Pt-OH-FeOx). The introduction of water vapor improves the catalytic activity of the Pt/Fe3O4 catalysts as it participates in a water-assisted dissociation process.
2018, 39(9): 1543-1551
doi: 10.1016/S1872-2067(18)63085-2
Abstract:
To enhance sulfur adsorption and reactive activity, ordered mesoporous Cu-ZnO-Al2O3 adsorbents were prepared by a novel one-pot evaporation-induced self-assembly strategy using P123 as a structure-directing agent and ethanol as the solvent for reactive adsorption desulfurization. The metal oxide precursor molecules around P123 micellized, and self-assembly simultaneously occurred during evaporation from an ethanol solution at 60℃, leading to the formation of the p6mm hexagonal symmetry mesoporous structure. Characterization results prove that the Cu-ZnO-Al2O3 adsorbents possess an ordered mesoporous structure with high thermal stability, large surface area (386-226 m2/g), large pore volume (0.60-0.46 cm3/g), and good dispersion of ZnO and Cu, which is beneficial for transforming S-compounds to ZnO. The sulfur saturation capacity of the ordered-mesoporous-structure Cu-ZnO-Al2O3 adsorbents is larger (49.4 mg/g) than that of the unordered mesoporous structure (13.5 mg/g).
To enhance sulfur adsorption and reactive activity, ordered mesoporous Cu-ZnO-Al2O3 adsorbents were prepared by a novel one-pot evaporation-induced self-assembly strategy using P123 as a structure-directing agent and ethanol as the solvent for reactive adsorption desulfurization. The metal oxide precursor molecules around P123 micellized, and self-assembly simultaneously occurred during evaporation from an ethanol solution at 60℃, leading to the formation of the p6mm hexagonal symmetry mesoporous structure. Characterization results prove that the Cu-ZnO-Al2O3 adsorbents possess an ordered mesoporous structure with high thermal stability, large surface area (386-226 m2/g), large pore volume (0.60-0.46 cm3/g), and good dispersion of ZnO and Cu, which is beneficial for transforming S-compounds to ZnO. The sulfur saturation capacity of the ordered-mesoporous-structure Cu-ZnO-Al2O3 adsorbents is larger (49.4 mg/g) than that of the unordered mesoporous structure (13.5 mg/g).
2018, 39(9): 1552-1559
doi: 10.1016/S1872-2067(18)63091-8
Abstract:
Despite the significance of hydrogen bonding in deep eutectic solvents (DESs) for desulfurization processes, little is understood about the relationship between the DES composition, hydrogen-bonding strength, and oxidative desulfurization activity. In this study, a new family of caprolactam-based acidic DESs was prepared with different molar ratios of caprolactam and oxalic acid. The prepared DESs were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and thermogravimetric analyses. These DESs were employed for oxidative desulfurization reactions and the desulfurization efficiency was found to vary regularly with the DES composition. The factors influencing the removal of dibenzothiophene were systematically investigated and the desulfurization efficiency of the caprolactam-based acidic DESs reached as high as 98% under optimal conditions. The removal of different sulfur compounds followed the order:dibenzothiophene > 4,6-dimethyldibenzothiophene > benzothiophene. The combined experimental data and characterization results revealed that the oxidative desulfurization efficiency of the system was influenced by the hydrogen bonding interactions with the DES, which can be optimized by adjusting the DES composition. These findings regarding hydrogen bonding in DESs provide new insight for better understanding of the mechanism of diesel deep desulfurization processes.
Despite the significance of hydrogen bonding in deep eutectic solvents (DESs) for desulfurization processes, little is understood about the relationship between the DES composition, hydrogen-bonding strength, and oxidative desulfurization activity. In this study, a new family of caprolactam-based acidic DESs was prepared with different molar ratios of caprolactam and oxalic acid. The prepared DESs were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and thermogravimetric analyses. These DESs were employed for oxidative desulfurization reactions and the desulfurization efficiency was found to vary regularly with the DES composition. The factors influencing the removal of dibenzothiophene were systematically investigated and the desulfurization efficiency of the caprolactam-based acidic DESs reached as high as 98% under optimal conditions. The removal of different sulfur compounds followed the order:dibenzothiophene > 4,6-dimethyldibenzothiophene > benzothiophene. The combined experimental data and characterization results revealed that the oxidative desulfurization efficiency of the system was influenced by the hydrogen bonding interactions with the DES, which can be optimized by adjusting the DES composition. These findings regarding hydrogen bonding in DESs provide new insight for better understanding of the mechanism of diesel deep desulfurization processes.
2018, 39(9): 1560-1567
doi: 10.1016/S1872-2067(18)63112-2
Abstract:
By taking advantage of silylanization, Al2O3 support was modified by organosilane and supported Pd-Cu-Clx/Al2O3 catalysts were prepared. The effects of hydrophobicity on catalyst stability during CO oxidation were investigated. The physicochemical properties and redox potential of the catalyst were characterized by N2 adsorption-desorption, XRD, H2-TPR, and XPS. In order to understand the relationship between the oxidation stability of CO and the presence of water, the CO oxidation mechanism was studied by in situ DRIFT. Support pretreatment markedly promoted catalyst stability during CO oxidation; CO conversion was 78% after 150 h at saturated humidity and freezing point. Modification led to an obvious decrease in chloride ion concentration and enhancement in hydrophobicity. The role of water in CO oxidation was complicated. The presence of water favored CO oxidation over active Pd+ species and Pd0 reoxidation by Cu2+ species. Meanwhile, water also inhibited the formation of the active Pd+ species and helped to produce carbonate species. Compared with the form of the carbonate species, the inhibition of water to produce active Pd+ species played the main detrimental role in catalyst stability.
By taking advantage of silylanization, Al2O3 support was modified by organosilane and supported Pd-Cu-Clx/Al2O3 catalysts were prepared. The effects of hydrophobicity on catalyst stability during CO oxidation were investigated. The physicochemical properties and redox potential of the catalyst were characterized by N2 adsorption-desorption, XRD, H2-TPR, and XPS. In order to understand the relationship between the oxidation stability of CO and the presence of water, the CO oxidation mechanism was studied by in situ DRIFT. Support pretreatment markedly promoted catalyst stability during CO oxidation; CO conversion was 78% after 150 h at saturated humidity and freezing point. Modification led to an obvious decrease in chloride ion concentration and enhancement in hydrophobicity. The role of water in CO oxidation was complicated. The presence of water favored CO oxidation over active Pd+ species and Pd0 reoxidation by Cu2+ species. Meanwhile, water also inhibited the formation of the active Pd+ species and helped to produce carbonate species. Compared with the form of the carbonate species, the inhibition of water to produce active Pd+ species played the main detrimental role in catalyst stability.
