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2014 Volume 35 Issue 4
2014, 35(4):
Abstract:
2014, 35(4): 453-456
doi: 10.1016/S1872-2067(14)60073-5
Abstract:
The oxide-supported metal catalysts constitute the most investigated catalyst in both academia and industry. This perspective highlights recent research progresses on the topic, which may shed light on the nature and location of the active sites.
The oxide-supported metal catalysts constitute the most investigated catalyst in both academia and industry. This perspective highlights recent research progresses on the topic, which may shed light on the nature and location of the active sites.
2014, 35(4): 457-461
doi: 10.1016/S1872-2067(14)60059-0
Abstract:
Core-shell TiO2@SiO2 was prepared using a combination of reverse microemulsion and precipitation methods and used as a heterogeneous catalyst for the transesterification of dimethyl carbonate and phenol. TiO2@SiO2 calcined at 200 ℃ gave the best catalytic performance. When the amount of catalyst was 0.20 g, the phenol conversion and transesterification selectivity were 41.8% and 100%, respectively. Transmission electron microscopy was used to characterize the core-shell TiO2@SiO2 structure, and the results showed that TiO2@SiO2 is bilayer with a TiO2 core of diameter 220-300 nm and SiO2 shell of thickness 40-60 nm. The TiO2@SiO2 was reusable, and phenol conversion remained above 40% when the TiO2@SiO2 was used four times. The catalytic performance of TiO2@SiO2 in the transesterification of dimethyl carbonate and phenol was promoted by the formation of Ti-O-Si bonds.
Core-shell TiO2@SiO2 was prepared using a combination of reverse microemulsion and precipitation methods and used as a heterogeneous catalyst for the transesterification of dimethyl carbonate and phenol. TiO2@SiO2 calcined at 200 ℃ gave the best catalytic performance. When the amount of catalyst was 0.20 g, the phenol conversion and transesterification selectivity were 41.8% and 100%, respectively. Transmission electron microscopy was used to characterize the core-shell TiO2@SiO2 structure, and the results showed that TiO2@SiO2 is bilayer with a TiO2 core of diameter 220-300 nm and SiO2 shell of thickness 40-60 nm. The TiO2@SiO2 was reusable, and phenol conversion remained above 40% when the TiO2@SiO2 was used four times. The catalytic performance of TiO2@SiO2 in the transesterification of dimethyl carbonate and phenol was promoted by the formation of Ti-O-Si bonds.
2014, 35(4): 462-467
doi: 10.1016/S1872-2067(14)60043-7
Abstract:
Methane has attracted extensive interest in recent years due to its potential application as a replacement of oil and a feedstock for valuable chemicals. Due to the large C-H bond energy, the conversion of methane into useful products has been a challenge. In the present study, density functional theory (DFT) calculations were performed to study the activation of the C-H bond of methane on the (001) and (011) planes of Co3O4, which showed that CH4 activation on Co3O4 nanocrystals was fairly easy with only small energy barriers (less than 1.1 eV). Surface Co-O ion pairs are the active site for C-H bond activation, where the two ions provide a synergistic effect for the activation of the strong C-H bond and yield surface Co-CH3 and O-H species. The Co3O4(011) surface is shown to be more reactive for C-H bond activation than the Co3O4(001) surface, which is consistent with previous experimental results. Our results suggest that methane oxidation on Co3O4 nanocrystals has strong crystal plane effect and structure sensitivity and the ion-pair active center plays a significant role in activating the strong C-H bond.
Methane has attracted extensive interest in recent years due to its potential application as a replacement of oil and a feedstock for valuable chemicals. Due to the large C-H bond energy, the conversion of methane into useful products has been a challenge. In the present study, density functional theory (DFT) calculations were performed to study the activation of the C-H bond of methane on the (001) and (011) planes of Co3O4, which showed that CH4 activation on Co3O4 nanocrystals was fairly easy with only small energy barriers (less than 1.1 eV). Surface Co-O ion pairs are the active site for C-H bond activation, where the two ions provide a synergistic effect for the activation of the strong C-H bond and yield surface Co-CH3 and O-H species. The Co3O4(011) surface is shown to be more reactive for C-H bond activation than the Co3O4(001) surface, which is consistent with previous experimental results. Our results suggest that methane oxidation on Co3O4 nanocrystals has strong crystal plane effect and structure sensitivity and the ion-pair active center plays a significant role in activating the strong C-H bond.
2014, 35(4): 468-473
doi: 10.1016/S1872-2067(14)60014-0
Abstract:
The effect of polytetrafluoroethylene (PTFE) distribution in the gas diffusion layer on water flooding in proton exchange membrane fuel cells was investigated. PTFE was introduced within micropores of carbon papers, to achieve hydrophobicity under different pressures. Carbon papers were subjected to vacuum conditions during immersion in PTFE solution to prepare gas diffusion layers. Residual gas within the carbon papers was eliminated, and PTFE evenly infused within the pores. Cross-sections of the carbon papers indicated that vacuum treatment improved PTFE distribution. The same PTFE content resulted in a decreased water contact angle of the carbon paper because of the greater PTFE content within the micropores. The proportions of hydrophobic and hydrophilic pores within the carbon papers were investigated. The proportion of hydrophobic pores increased during the vacuum treatment. Membrane electrode assemblies (MEAs) were fabricated using the treated hydrophobic carbon papers as gas diffusion layers and were evaluated in a full-sized fuel cell. The uniform PTFE distribution of the carbon paper benefited fuel performance. Electrochemical impedance spectroscopy indicated that the improved MEA possessed favorable resistance to water flooding.
The effect of polytetrafluoroethylene (PTFE) distribution in the gas diffusion layer on water flooding in proton exchange membrane fuel cells was investigated. PTFE was introduced within micropores of carbon papers, to achieve hydrophobicity under different pressures. Carbon papers were subjected to vacuum conditions during immersion in PTFE solution to prepare gas diffusion layers. Residual gas within the carbon papers was eliminated, and PTFE evenly infused within the pores. Cross-sections of the carbon papers indicated that vacuum treatment improved PTFE distribution. The same PTFE content resulted in a decreased water contact angle of the carbon paper because of the greater PTFE content within the micropores. The proportions of hydrophobic and hydrophilic pores within the carbon papers were investigated. The proportion of hydrophobic pores increased during the vacuum treatment. Membrane electrode assemblies (MEAs) were fabricated using the treated hydrophobic carbon papers as gas diffusion layers and were evaluated in a full-sized fuel cell. The uniform PTFE distribution of the carbon paper benefited fuel performance. Electrochemical impedance spectroscopy indicated that the improved MEA possessed favorable resistance to water flooding.
2014, 35(4): 474-480
doi: 10.1016/S1872-2067(12)60752-9
Abstract:
7-Aryl-8H-benzo[f]indeno[2,1-b]quinoline-8-one derivatives were synthesized by means of a one-pot condensation of 2-naphthylamine, aromatic aldehydes, and indane-1,3-dione in ethanol under refluxing conditions in the presence of poly(4-vinylpyridinium) hydrogen sulfate, a solid acid catalyst. This method has the advantages of high yield, clean reaction, simple methodology, and short reaction time. The catalyst could be recycled and reused four times without significant loss of activity. The structure of the novel compounds was confirmed by IR, 1H NMR, and 13C NMR spectroscopy and elemental analysis.？？？？？？
7-Aryl-8H-benzo[f]indeno[2,1-b]quinoline-8-one derivatives were synthesized by means of a one-pot condensation of 2-naphthylamine, aromatic aldehydes, and indane-1,3-dione in ethanol under refluxing conditions in the presence of poly(4-vinylpyridinium) hydrogen sulfate, a solid acid catalyst. This method has the advantages of high yield, clean reaction, simple methodology, and short reaction time. The catalyst could be recycled and reused four times without significant loss of activity. The structure of the novel compounds was confirmed by IR, 1H NMR, and 13C NMR spectroscopy and elemental analysis.？？？？？？
2014, 35(4): 481-489
doi: 10.1016/S1872-2067(14)60010-3
Abstract:
Modified multi-walled carbon nanotube-supported TiO2 samples were prepared and used as an efficient heterogeneous catalyst for the transesterification of dimethyl carbonate with phenol. The catalysts were characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption-desorption, and X-ray powder diffraction. The results showed that the catalyst, which was prepared using a low concentration (0.4%) of ammonium hydroxide as the precipitant instead of ionized water, had better catalytic activity, separability, and reusability properties. The effects of the TiO2 loading, amount of catalyst and reaction time on the performance of the transesterification reaction were also studied. Under the optimum reaction conditions, the conversion of phenol reached 42.5% with over 99.9% selectivity for methyl phenyl carbonate and diphenyl carbonate. The catalyst could be reused for the transesterification in four runs with only slight loss of its catalytic activity.
Modified multi-walled carbon nanotube-supported TiO2 samples were prepared and used as an efficient heterogeneous catalyst for the transesterification of dimethyl carbonate with phenol. The catalysts were characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption-desorption, and X-ray powder diffraction. The results showed that the catalyst, which was prepared using a low concentration (0.4%) of ammonium hydroxide as the precipitant instead of ionized water, had better catalytic activity, separability, and reusability properties. The effects of the TiO2 loading, amount of catalyst and reaction time on the performance of the transesterification reaction were also studied. Under the optimum reaction conditions, the conversion of phenol reached 42.5% with over 99.9% selectivity for methyl phenyl carbonate and diphenyl carbonate. The catalyst could be reused for the transesterification in four runs with only slight loss of its catalytic activity.
2014, 35(4): 490-495
doi: 10.1016/S1872-2067(14)60011-5
Abstract:
An efficient, environmentally friendly procedure for the synthesis of amidoalkyl naphthols through the one-pot, three-component reaction of β-naphthol, aryl aldehydes, and acetamide in the presence of a carbon-based solid acid under thermal solvent-free conditions is described. The beneficial features of this new synthetic approach include short reaction time, high yields, clean reaction profiles, and a simple work-up procedure. Furthermore, the catalyst can be readily recycled and reused four times without obvious significant loss of activity. The structure of the catalyst was confirmed by Fourier transform infrared spectroscopy, N2 adsorption/desorption analysis, and X-ray diffraction.
An efficient, environmentally friendly procedure for the synthesis of amidoalkyl naphthols through the one-pot, three-component reaction of β-naphthol, aryl aldehydes, and acetamide in the presence of a carbon-based solid acid under thermal solvent-free conditions is described. The beneficial features of this new synthetic approach include short reaction time, high yields, clean reaction profiles, and a simple work-up procedure. Furthermore, the catalyst can be readily recycled and reused four times without obvious significant loss of activity. The structure of the catalyst was confirmed by Fourier transform infrared spectroscopy, N2 adsorption/desorption analysis, and X-ray diffraction.
2014, 35(4): 496-500
doi: 10.1016/S1872-2067(14)60012-7
Abstract:
The promotion effect of alkali metal halides toward the AlCl3-catalyzed conversion of glucose to 5-hydroxymethylfurfural (HMF) was investigated. The results show that NaF inhibited the reaction. However, NaI and NaBr promoted the reaction significantly, and the promotion effect of NaI was more obvious than that of NaBr. In N,N-dimethylacetamide (DMAC), when NaI was used as an additive for the AlCl3-catalyzed conversion of glucose at 130 ℃ for 15 min, glucose conversion increased from 71% to 86%, and the HMF yield increased from 36% to 62%. The AlCl3-NaI-DMAC system could also be used for the catalytic conversion of other carbohydrates such as fructose, mannose, sucrose, maltose, cellobiose, and inulin to HMF. When sucrose was used as the feedstock, a 63% HMF yield was achieved.
The promotion effect of alkali metal halides toward the AlCl3-catalyzed conversion of glucose to 5-hydroxymethylfurfural (HMF) was investigated. The results show that NaF inhibited the reaction. However, NaI and NaBr promoted the reaction significantly, and the promotion effect of NaI was more obvious than that of NaBr. In N,N-dimethylacetamide (DMAC), when NaI was used as an additive for the AlCl3-catalyzed conversion of glucose at 130 ℃ for 15 min, glucose conversion increased from 71% to 86%, and the HMF yield increased from 36% to 62%. The AlCl3-NaI-DMAC system could also be used for the catalytic conversion of other carbohydrates such as fructose, mannose, sucrose, maltose, cellobiose, and inulin to HMF. When sucrose was used as the feedstock, a 63% HMF yield was achieved.
2014, 35(4): 501-508
doi: 10.1016/S1872-2067(14)60019-X
Abstract:
A multiwall carbon nanotube modified electrode prepared by incorporating multiwall carbon nanotubes in the electrode of a sensor and naphthol green as a homogeneous mediator was used as a voltammetric sensor for the determination of N-actylcysteine (N-AC) in the presence of tryptophan (Trp). The voltammograms of differential pulse voltammetry of N-AC in a mixture with Trp were separated from each other by a potential difference of 200 mV, which allowed the determination of both N-AC and Trp simultaneously. Under the optimum conditions, the electrocatalytic currents increased linearly with N-AC concentration in the range of 0.25-400 μmol/L (two linear segments with different slopes). The detection limit for N-AC was 0.08 μmol/L. The kinetic parameters of the system were determined using electrochemical methods. The method was applied for the determination of N-AC in drug and urine samples.
A multiwall carbon nanotube modified electrode prepared by incorporating multiwall carbon nanotubes in the electrode of a sensor and naphthol green as a homogeneous mediator was used as a voltammetric sensor for the determination of N-actylcysteine (N-AC) in the presence of tryptophan (Trp). The voltammograms of differential pulse voltammetry of N-AC in a mixture with Trp were separated from each other by a potential difference of 200 mV, which allowed the determination of both N-AC and Trp simultaneously. Under the optimum conditions, the electrocatalytic currents increased linearly with N-AC concentration in the range of 0.25-400 μmol/L (two linear segments with different slopes). The detection limit for N-AC was 0.08 μmol/L. The kinetic parameters of the system were determined using electrochemical methods. The method was applied for the determination of N-AC in drug and urine samples.
2014, 35(4): 509-513
doi: 10.1016/S1872-2067(14)60016-4
Abstract:
Nitrogen-doped graphene (NG) with a nitrogen content from 4.05 wt% to 5.47 wt% was rapidly prepared via microwave heating of graphene under NH3 flow. The as-synthesized NG samples were then used as electrocatalysts in the oxygen reduction reaction (ORR) in alkaline solution. The NG samples showed excellent ORR catalytic activity with an onset potential of 0.17 V, which is comparable to that of commercial Pt/C electrocatalyst (0.21 V). The structure, composition, and nitrogen species of the NG samples were examined by transmission electron microscopy, Raman spectroscopy, elemental analysis and X-ray photoelectron spectroscopy. The onset potential increases with the content of graphite nitrogen in the NG samples, indicating that graphite nitrogen might be the main factor controlling the performance of the NG samples in the ORR. The results showed that NG prepared by rapid microwave heating is a promising ORR catalyst for fuel cells.
Nitrogen-doped graphene (NG) with a nitrogen content from 4.05 wt% to 5.47 wt% was rapidly prepared via microwave heating of graphene under NH3 flow. The as-synthesized NG samples were then used as electrocatalysts in the oxygen reduction reaction (ORR) in alkaline solution. The NG samples showed excellent ORR catalytic activity with an onset potential of 0.17 V, which is comparable to that of commercial Pt/C electrocatalyst (0.21 V). The structure, composition, and nitrogen species of the NG samples were examined by transmission electron microscopy, Raman spectroscopy, elemental analysis and X-ray photoelectron spectroscopy. The onset potential increases with the content of graphite nitrogen in the NG samples, indicating that graphite nitrogen might be the main factor controlling the performance of the NG samples in the ORR. The results showed that NG prepared by rapid microwave heating is a promising ORR catalyst for fuel cells.
2014, 35(4): 514-523
doi: 10.1016/S1872-2067(14)60018-8
Abstract:
A factorial experimental design was combined with response surface methodology (RSM) to optimize the catalyzed CO2 consumption by coke deposition and syngas production during the dry reforming of CH4. The CH4/CO2 feed ratio and the reaction temperature were chosen as the variables, and the selected responses were CH4 and CO2 conversion, the H2/CO ratio, and coke deposition. The optimal reaction conditions were found to be a CH4/CO2 feed ratio of approximately 3 at 700 ℃, producing a large quantity of coke and realizing high CO2 conversion. Furthermore, Raman results showed that the CH4/CO2 ratio and reaction temperature affect the system's response, particularly the characteristics of the coke produced, which indicates the formation of carbon nanotubes and amorphous carbon.
A factorial experimental design was combined with response surface methodology (RSM) to optimize the catalyzed CO2 consumption by coke deposition and syngas production during the dry reforming of CH4. The CH4/CO2 feed ratio and the reaction temperature were chosen as the variables, and the selected responses were CH4 and CO2 conversion, the H2/CO ratio, and coke deposition. The optimal reaction conditions were found to be a CH4/CO2 feed ratio of approximately 3 at 700 ℃, producing a large quantity of coke and realizing high CO2 conversion. Furthermore, Raman results showed that the CH4/CO2 ratio and reaction temperature affect the system's response, particularly the characteristics of the coke produced, which indicates the formation of carbon nanotubes and amorphous carbon.
2014, 35(4): 524-531
doi: 10.1016/S1872-2067(14)60017-6
Abstract:
A new biomimetic catalyst (M-CYC) is formed from the combination of CYC (a derivative of 1,4,7,10,13,16,19,22,25,28,31-undecaaza-cyclotritriacontane-2,5,8,11,14,17,20,23,26,29,32-undeca acyl) and Ce(Ⅲ, M) in aqueous solution. The interaction between this complex and DNA was studied using electronic absorption spectroscopy, fluorescence spectroscopy, and gel electrophoresis. The results indicated that M-CYC and calf thymus DNA (pUC19 DNA) interacted via intercalation. The apparent binding constant of the complex with DNA was determined to be 2.0×104 L/mol at pH 8.16. Based on gel electrophoresis analysis, M-CYC was shown to nick the circular plasmid pUC19 DNA in the presence of a free radical scavenger. The nicking of DNA serves as a model of hydrolyzed cleavage.
A new biomimetic catalyst (M-CYC) is formed from the combination of CYC (a derivative of 1,4,7,10,13,16,19,22,25,28,31-undecaaza-cyclotritriacontane-2,5,8,11,14,17,20,23,26,29,32-undeca acyl) and Ce(Ⅲ, M) in aqueous solution. The interaction between this complex and DNA was studied using electronic absorption spectroscopy, fluorescence spectroscopy, and gel electrophoresis. The results indicated that M-CYC and calf thymus DNA (pUC19 DNA) interacted via intercalation. The apparent binding constant of the complex with DNA was determined to be 2.0×104 L/mol at pH 8.16. Based on gel electrophoresis analysis, M-CYC was shown to nick the circular plasmid pUC19 DNA in the presence of a free radical scavenger. The nicking of DNA serves as a model of hydrolyzed cleavage.
2014, 35(4): 532-539
doi: 10.1016/S1872-2067(14)60025-5
Abstract:
Polyoxometalate-based heterogeneous materials were prepared by the immobilization of 12-phosphomolybdic acid (PMA) on periodic mesoporous organosilicas containing embedded imidazolium cations (PMO-ILs). The resulting hybrid materials (PMA@PMO-ILs) were characterized by N2 adsorption-desorption, powder X-ray diffraction, atomic adsorption spectroscopy, thermogravimetric and differential thermal analyses, Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, and solid-state cross-polarization magic angle spinning nuclear magnetic resonance. PMA was electrostatically immobilized on the surface and in the channels of PMO-ILs. The PMO-IL support and PMA structures were retained during the preparation processes. The catalytic properties of the PMA@PMO-ILs were evaluated for the liquid-phase epoxidation of cyclooctene. PMA@PMO-ILs were catalytically active, with nearly 100% selectivity to cyclooctene epoxide using tert-butyl hydroperoxide as the oxidant. The catalysts could be reused four times without obvious loss of activity or selectivity under identical reaction conditions. Imidazolium cations in the PMO-IL framework improved the stability and recyclability of the PMA immobilized catalysts.
Polyoxometalate-based heterogeneous materials were prepared by the immobilization of 12-phosphomolybdic acid (PMA) on periodic mesoporous organosilicas containing embedded imidazolium cations (PMO-ILs). The resulting hybrid materials (PMA@PMO-ILs) were characterized by N2 adsorption-desorption, powder X-ray diffraction, atomic adsorption spectroscopy, thermogravimetric and differential thermal analyses, Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, and solid-state cross-polarization magic angle spinning nuclear magnetic resonance. PMA was electrostatically immobilized on the surface and in the channels of PMO-ILs. The PMO-IL support and PMA structures were retained during the preparation processes. The catalytic properties of the PMA@PMO-ILs were evaluated for the liquid-phase epoxidation of cyclooctene. PMA@PMO-ILs were catalytically active, with nearly 100% selectivity to cyclooctene epoxide using tert-butyl hydroperoxide as the oxidant. The catalysts could be reused four times without obvious loss of activity or selectivity under identical reaction conditions. Imidazolium cations in the PMO-IL framework improved the stability and recyclability of the PMA immobilized catalysts.
2014, 35(4): 540-545
doi: 10.1016/S1872-2067(14)60021-8
Abstract:
Covalent organic polymers are an emerging class of materials with potential applications in areas including molecular separation, gas sorption, and catalysis. A novel fully conjugated organic polymer bearing bis(imino)pyridine (COP-BIP) and its catalytic function are reported here. Unlike previous COP materials, the imine bonds of COP-BIP act as both linkages and complexation sites for the binding of metal ions. A clear structure is presented based on ultraviolet-visible, Fourier transform infrared, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry characterization. The COP-BIP materials are thermally stable up to 440 ℃ and are insoluble in conventional solvents. In addition, COP-BIP complexes Pd ions on bis(imino)pyridine sites and forms a heterogeneous catalyst, which exhibits excellent catalytic activity in the Suzuki-Miyaura C-C coupling reaction.
Covalent organic polymers are an emerging class of materials with potential applications in areas including molecular separation, gas sorption, and catalysis. A novel fully conjugated organic polymer bearing bis(imino)pyridine (COP-BIP) and its catalytic function are reported here. Unlike previous COP materials, the imine bonds of COP-BIP act as both linkages and complexation sites for the binding of metal ions. A clear structure is presented based on ultraviolet-visible, Fourier transform infrared, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry characterization. The COP-BIP materials are thermally stable up to 440 ℃ and are insoluble in conventional solvents. In addition, COP-BIP complexes Pd ions on bis(imino)pyridine sites and forms a heterogeneous catalyst, which exhibits excellent catalytic activity in the Suzuki-Miyaura C-C coupling reaction.
2014, 35(4): 546-552
doi: 10.1016/S1872-2067(14)60028-0
Abstract:
A Ni/montmorillonite (MMT) catalyst was prepared by an impregnation method using cetyltrimethylammonium bromide (CTAB)-pillared MMT as the supporting matrix and was characterized using infrared spectroscopy, X-ray diffraction, H2 temperature-programmed desorption, N2 adsorption-desorption, and ultraviolet diffuse reflectance spectroscopy. The catalytic activity of the Ni/MMT for the hydrogenation of naphthalene was also evaluated. The results show that the organic modification of MMT greatly improved the Ni dispersion and textural properties of the Ni/MMT catalyst. The as-prepared Ni/MMT catalyst showed high naphthalene conversion (88.2%) in the hydrogenation reaction; this is much higher than those achieved using Ni supported on pristine MMT (13.1%), Al2O3-pillared MMT (24.2%), and SBA-15 (68.2%). As a result of thermal decomposition of CTAB pillars during reduction of the Ni/MMT catalyst, the CTAB pillars mainly play a role in the Ni/MMT catalyst during impregnation. A mechanism for the promotion of the Ni/MMT catalytic activity by organic modification during impregnation is proposed.
A Ni/montmorillonite (MMT) catalyst was prepared by an impregnation method using cetyltrimethylammonium bromide (CTAB)-pillared MMT as the supporting matrix and was characterized using infrared spectroscopy, X-ray diffraction, H2 temperature-programmed desorption, N2 adsorption-desorption, and ultraviolet diffuse reflectance spectroscopy. The catalytic activity of the Ni/MMT for the hydrogenation of naphthalene was also evaluated. The results show that the organic modification of MMT greatly improved the Ni dispersion and textural properties of the Ni/MMT catalyst. The as-prepared Ni/MMT catalyst showed high naphthalene conversion (88.2%) in the hydrogenation reaction; this is much higher than those achieved using Ni supported on pristine MMT (13.1%), Al2O3-pillared MMT (24.2%), and SBA-15 (68.2%). As a result of thermal decomposition of CTAB pillars during reduction of the Ni/MMT catalyst, the CTAB pillars mainly play a role in the Ni/MMT catalyst during impregnation. A mechanism for the promotion of the Ni/MMT catalytic activity by organic modification during impregnation is proposed.
2014, 35(4): 553-559
doi: 10.1016/S1872-2067(14)60053-X
Abstract:
A novel ultraviolet (UV) spectrophotometric method for evaluating lipase transesterification activity in organic solvents is described. The model reaction was lipase-catalyzed transesterification between p-nitrophenyl palmitate (pNPP) and n-butanol in n-hexane at 30 ℃. The conversion of pNPP to p-nitrophenol was monitored by measuring UV absorbance changes at 310 nm. Seven commercial lipases were tested using this method, and the results were similar to those obtained using gas chromatography. The UV spectrophotometric method was used to investigate the kinetics of the Lipozyme TL IM-catalyzed reaction of pNPP, and the correlation between synthetic activity and biocatalyst concentration was determined. The method was also used to investigate the Lipozyme TL IM-catalyzed transesterification properties, namely solvent effect, acyl acceptor specificity, alcohol tolerance, optimum reaction temperature, and thermostability.
A novel ultraviolet (UV) spectrophotometric method for evaluating lipase transesterification activity in organic solvents is described. The model reaction was lipase-catalyzed transesterification between p-nitrophenyl palmitate (pNPP) and n-butanol in n-hexane at 30 ℃. The conversion of pNPP to p-nitrophenol was monitored by measuring UV absorbance changes at 310 nm. Seven commercial lipases were tested using this method, and the results were similar to those obtained using gas chromatography. The UV spectrophotometric method was used to investigate the kinetics of the Lipozyme TL IM-catalyzed reaction of pNPP, and the correlation between synthetic activity and biocatalyst concentration was determined. The method was also used to investigate the Lipozyme TL IM-catalyzed transesterification properties, namely solvent effect, acyl acceptor specificity, alcohol tolerance, optimum reaction temperature, and thermostability.
2014, 35(4): 560-564
doi: 10.1016/S1872-2067(14)60034-6
Abstract:
Cu doped ZnO nanocrystalline powder (10 mol%) has been found to be an efficient catalyst for the one-pot multi-component synthesis of fully substituted new indeno[1,2-b]pyridines through a combination of 1,3-indandione, propiophenone or acetophenone derivatives, aromatic aldehydes, and ammonium acetate in ethanol/H2O at room temperature. The methodology is mild, efficient and high to excellent yielding.
Cu doped ZnO nanocrystalline powder (10 mol%) has been found to be an efficient catalyst for the one-pot multi-component synthesis of fully substituted new indeno[1,2-b]pyridines through a combination of 1,3-indandione, propiophenone or acetophenone derivatives, aromatic aldehydes, and ammonium acetate in ethanol/H2O at room temperature. The methodology is mild, efficient and high to excellent yielding.
2014, 35(4): 565-572
doi: 10.1016/S1872-2067(14)60027-9
Abstract:
A carbon paste electrode modified with 2-((7-(2,5-dihydrobenzylideneamino)heptylimino)methyl) benzene-1,4-diol (DHB) and carbon nanotubes were used to simultaneously determine the concentrations of isoproterenol (IP), uric acid (UA), and folic acid (FA) in solution. First, cyclic voltammetry was used to investigate the redox properties of the modified electrode at various scan rates. Next, the mediated oxidation of IP at the modified electrode is described. At the optimum pH of 7.0, the oxidation of IP occurs at a potential about 90 mV less than that of an unmodified carbon paste electrode. Based on the results of differential pulse voltammetry (DPV), the oxidation of IP showed a dynamic range between 10 and 6000 μmol/L, and a detection limit of 1.24 μmol/L. Finally, DPV was used to simultaneously determine the concentrations of IP, UA, and FA in solution at the modified electrode.
A carbon paste electrode modified with 2-((7-(2,5-dihydrobenzylideneamino)heptylimino)methyl) benzene-1,4-diol (DHB) and carbon nanotubes were used to simultaneously determine the concentrations of isoproterenol (IP), uric acid (UA), and folic acid (FA) in solution. First, cyclic voltammetry was used to investigate the redox properties of the modified electrode at various scan rates. Next, the mediated oxidation of IP at the modified electrode is described. At the optimum pH of 7.0, the oxidation of IP occurs at a potential about 90 mV less than that of an unmodified carbon paste electrode. Based on the results of differential pulse voltammetry (DPV), the oxidation of IP showed a dynamic range between 10 and 6000 μmol/L, and a detection limit of 1.24 μmol/L. Finally, DPV was used to simultaneously determine the concentrations of IP, UA, and FA in solution at the modified electrode.
2014, 35(4): 573-578
doi: 10.1016/S1872-2067(14)60030-9
Abstract:
An efficient solvent-free protocol for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from the condensation of 2-naphthol with arylaldehydes, using acetic acid functionalized imidazolium salts (1-carboxymethyl-3-methylimidazolium bromide ([cmmim]Br) and 1-carboxymethy1-3-methylimidazolium tetrafluoroborate ([cmmim]BF4) as reusable catalysts, has been developed. The turn over frequency on the catalysts is several times higher than the other previously reported catalysts. Also, thermal gravimetric analysis and powder X-ray diffraction pattern of the catalysts have been studied.
An efficient solvent-free protocol for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from the condensation of 2-naphthol with arylaldehydes, using acetic acid functionalized imidazolium salts (1-carboxymethyl-3-methylimidazolium bromide ([cmmim]Br) and 1-carboxymethy1-3-methylimidazolium tetrafluoroborate ([cmmim]BF4) as reusable catalysts, has been developed. The turn over frequency on the catalysts is several times higher than the other previously reported catalysts. Also, thermal gravimetric analysis and powder X-ray diffraction pattern of the catalysts have been studied.
2014, 35(4): 579-589
doi: 10.1016/S1872-2067(14)60037-1
Abstract:
The spin-forbidden mechanism of the reaction between N2O and C2H6 catalyzed by Co+ has been investigated using UB3LYP density functional theory. The Harvey method has been applied to optimize five minimum energy crossing points (MECP) on both triplet and quintet potential energy surfaces. Possible spin inversion processes are discussed by means of spin-orbit coupling calculations. According to the calculation of probability of electron hopping using the Landau-Zener formula, effective intersystem crossing may occur at each MECP. The energetic span model proposed by Kozuch has been applied to the catalytic cycles, and shows the turnover frequency reaches 3.35×10-21 s-1 when Co+ catalyzes the reaction to produce CH3CHO at 298K.
The spin-forbidden mechanism of the reaction between N2O and C2H6 catalyzed by Co+ has been investigated using UB3LYP density functional theory. The Harvey method has been applied to optimize five minimum energy crossing points (MECP) on both triplet and quintet potential energy surfaces. Possible spin inversion processes are discussed by means of spin-orbit coupling calculations. According to the calculation of probability of electron hopping using the Landau-Zener formula, effective intersystem crossing may occur at each MECP. The energetic span model proposed by Kozuch has been applied to the catalytic cycles, and shows the turnover frequency reaches 3.35×10-21 s-1 when Co+ catalyzes the reaction to produce CH3CHO at 298K.
2014, 35(4): 590-598
doi: 10.1016/S1872-2067(14)60056-5
Abstract:
β-cyclodextrin-functionalized cellulose was prepared from cellulose and β-cyclodextrin crosslinked with epichlorohydrin. The supramolecular polymer has been used as a heterogeneous catalyst for the synthesis of benzaldehyde under mild reaction conditions with high activity and yield. The catalyst was easily recovered and reused without significant activity loss. The β-cyclodextrin in the polymer formed host-guest complexes with cinnamaldehyde via noncovalent bonding. In addition, multiple interactions were observed between β-cyclodextrin and the substrate via intermolecular O-H…O hydrogen bonding. The significant promotion for the catalytic performance could be attributed to the synergistic effects of hydrogen bonding.
β-cyclodextrin-functionalized cellulose was prepared from cellulose and β-cyclodextrin crosslinked with epichlorohydrin. The supramolecular polymer has been used as a heterogeneous catalyst for the synthesis of benzaldehyde under mild reaction conditions with high activity and yield. The catalyst was easily recovered and reused without significant activity loss. The β-cyclodextrin in the polymer formed host-guest complexes with cinnamaldehyde via noncovalent bonding. In addition, multiple interactions were observed between β-cyclodextrin and the substrate via intermolecular O-H…O hydrogen bonding. The significant promotion for the catalytic performance could be attributed to the synergistic effects of hydrogen bonding.
