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2014 Volume 35 Issue 10
2014, 35(10):
Abstract:
2014, 35(10): 1591-1608
doi: 10.1016/S1872-2067(14)60082-6
Abstract:
Revealing the structure of supported metal oxide catalysts is a prerequisite for establishing the structure-catalysis relationship. Among a variety of characterization techniques, multi-wavelength Raman spectroscopy, combining resonance Raman and non-resonance Raman with different excitation wavelengths, has recently emerged as a particularly powerful tool in not only identifying but also quantifying the structure of supported metal oxide clusters. In this review, we make use of two supported vanadia systems, VOx/SiO2 and VOx/CeO2, as examples to showcase how one can employ this technique to investigate the heterogeneous structure of active oxide clusters and to understand the complex interaction between the oxide clusters and the support. The qualitative and quantitative structural information gained from the multi-wavelength Raman spectroscopy can be utilized to provide fundamental insights for designing more efficient supported metal oxide catalysts.
Revealing the structure of supported metal oxide catalysts is a prerequisite for establishing the structure-catalysis relationship. Among a variety of characterization techniques, multi-wavelength Raman spectroscopy, combining resonance Raman and non-resonance Raman with different excitation wavelengths, has recently emerged as a particularly powerful tool in not only identifying but also quantifying the structure of supported metal oxide clusters. In this review, we make use of two supported vanadia systems, VOx/SiO2 and VOx/CeO2, as examples to showcase how one can employ this technique to investigate the heterogeneous structure of active oxide clusters and to understand the complex interaction between the oxide clusters and the support. The qualitative and quantitative structural information gained from the multi-wavelength Raman spectroscopy can be utilized to provide fundamental insights for designing more efficient supported metal oxide catalysts.
2014, 35(10): 1609-1618
doi: 10.1016/S1872-2067(14)60170-4
Abstract:
Photocatalysis has attracted much attention for its promise in converting solar energy to chemical energy and in degrading various pollutants. Many recent investigations have demonstrated photocatalysts with well-defined junctions between two semiconductors with matched electronic band structures. Such structures effectively facilitate charge transfer and suppress recombination of photogenerated electrons and holes, leading to extremely high activity and stability. In this review, we focus on the influence of the heterojunction on the performance of semiconductor photocatalysts, including TiO2-based, ZnO-based, and Ag-based semiconductor photocatalysts. We also investigate fabrication methods for heterojunctions and attempt to understand the mechanisms behind photocatalysis. Finally, we propose challenges to design and clarify the mechanism for enhancing the effect of the heterojunction on photocatalyst performance.
Photocatalysis has attracted much attention for its promise in converting solar energy to chemical energy and in degrading various pollutants. Many recent investigations have demonstrated photocatalysts with well-defined junctions between two semiconductors with matched electronic band structures. Such structures effectively facilitate charge transfer and suppress recombination of photogenerated electrons and holes, leading to extremely high activity and stability. In this review, we focus on the influence of the heterojunction on the performance of semiconductor photocatalysts, including TiO2-based, ZnO-based, and Ag-based semiconductor photocatalysts. We also investigate fabrication methods for heterojunctions and attempt to understand the mechanisms behind photocatalysis. Finally, we propose challenges to design and clarify the mechanism for enhancing the effect of the heterojunction on photocatalyst performance.
2014, 35(10): 1619-1640
doi: 10.1016/S1872-2067(14)60118-2
Abstract:
Ammonia synthesis catalyst found by Haber-Bosch achieves its history of 100 years. The current understanding and enlightenment from foundation and development of ammonia synthesis catalyst are reviewed, and its future and facing new challenge remained today are expected. Catalytic ammonia synthesis technology has played a central role in the development of the chemical industry during the 20th century. During 100 years, ammonia synthesis catalyst has come through diversified seedtime such as Fe3O4-based iron catalysts, Fe1-xO-based iron catalysts, ruthenium-based catalysts, and discovery of a Co-Mo-N system. Often new techniques, methods, and theories of catalysis have initially been developed and applied in connection with studies of this system. Similarly, new discoveries in the field of ammonia synthesis have been extended to other fields of catalysis. There is no other practically relevant reaction that leads to such a close interconnection between theory, model catalysis, and experiment as the high-pressure synthesis of ammonia. Catalytic synthesis ammonia reaction is yet a perfect model system for academic research in the field of heterogeneous catalysis. Understanding the mechanism and the translation of the knowledge into technical perfection has become a fundamental criterion for scientific development in catalysis research. The never-ending story has not ended yet. In addition to questions about the elementary steps of the reaction and the importance of the real structure and subnitrides for the catalyst efficiency, as well as the wide-open question about new catalyst materials, there are also different challenges thrown down by theory for the experimentalist in the prediction of a biomimetic ammonia-synthesis path at room temperature and atmospheric pressure including electrocatalysis, photocatalysis and biomimetic nitrogen fixation.
Ammonia synthesis catalyst found by Haber-Bosch achieves its history of 100 years. The current understanding and enlightenment from foundation and development of ammonia synthesis catalyst are reviewed, and its future and facing new challenge remained today are expected. Catalytic ammonia synthesis technology has played a central role in the development of the chemical industry during the 20th century. During 100 years, ammonia synthesis catalyst has come through diversified seedtime such as Fe3O4-based iron catalysts, Fe1-xO-based iron catalysts, ruthenium-based catalysts, and discovery of a Co-Mo-N system. Often new techniques, methods, and theories of catalysis have initially been developed and applied in connection with studies of this system. Similarly, new discoveries in the field of ammonia synthesis have been extended to other fields of catalysis. There is no other practically relevant reaction that leads to such a close interconnection between theory, model catalysis, and experiment as the high-pressure synthesis of ammonia. Catalytic synthesis ammonia reaction is yet a perfect model system for academic research in the field of heterogeneous catalysis. Understanding the mechanism and the translation of the knowledge into technical perfection has become a fundamental criterion for scientific development in catalysis research. The never-ending story has not ended yet. In addition to questions about the elementary steps of the reaction and the importance of the real structure and subnitrides for the catalyst efficiency, as well as the wide-open question about new catalyst materials, there are also different challenges thrown down by theory for the experimentalist in the prediction of a biomimetic ammonia-synthesis path at room temperature and atmospheric pressure including electrocatalysis, photocatalysis and biomimetic nitrogen fixation.
2014, 35(10): 1641-1652
doi: 10.1016/S1872-2067(14)60193-5
Abstract:
The oxidation of para-xylene to terephthalic acid has been commercialised as the AMOCO process (Co/Mn/Br) that uses a homogeneous catalyst of cobalt and manganese together with a corrosive bromide compound as a promoter. This process is conducted in acidic medium at a high temperature (175-225 ℃). Concerns over environmental and safety issues have driven studies to find milder oxidation reactions of para-xylene. This review discussed past and current progress in the oxidation of para-xylene process. The discussion concentrates on the approach of green chemistry including (1) using heterogeneous catalysts with promising high selectivity and mild reaction condition, (2) application of carbon dioxide as a co-oxidant, and (3) application of alternative promoters. The optimisation of para-xylene oxidation was also outlined.
The oxidation of para-xylene to terephthalic acid has been commercialised as the AMOCO process (Co/Mn/Br) that uses a homogeneous catalyst of cobalt and manganese together with a corrosive bromide compound as a promoter. This process is conducted in acidic medium at a high temperature (175-225 ℃). Concerns over environmental and safety issues have driven studies to find milder oxidation reactions of para-xylene. This review discussed past and current progress in the oxidation of para-xylene process. The discussion concentrates on the approach of green chemistry including (1) using heterogeneous catalysts with promising high selectivity and mild reaction condition, (2) application of carbon dioxide as a co-oxidant, and (3) application of alternative promoters. The optimisation of para-xylene oxidation was also outlined.
2014, 35(10): 1653-1660
doi: 10.1016/S1872-2067(14)60132-7
Abstract:
Gold nanoclusters or nanoparticles on various supports (CeO2, activated carbon, HY, REY, and NaY) were investigated for glycerol oxidation in the aqueous phase under mild conditions. Compared with other catalysts, Au/HY showed remarkable catalytic performance in forming dicarboxylic acid (tartronic acid) over the monocarboxylic acid (glyceric acid) or the C-C cleavage product (oxalic acid). Au/HY achieved 98% conversion of glycerol and 80% yield of tartronic acid at 60 ℃ under 0.3 MPa O2. Further characterization showed that the small size of Au clusters is the key factor for the high oxidation performance. In situ Fourier transform infrared spectroscopy revealed that glycerol was first transformed to glyceric acid, and then glyceric acid was directly oxidized to tartronic acid.
Gold nanoclusters or nanoparticles on various supports (CeO2, activated carbon, HY, REY, and NaY) were investigated for glycerol oxidation in the aqueous phase under mild conditions. Compared with other catalysts, Au/HY showed remarkable catalytic performance in forming dicarboxylic acid (tartronic acid) over the monocarboxylic acid (glyceric acid) or the C-C cleavage product (oxalic acid). Au/HY achieved 98% conversion of glycerol and 80% yield of tartronic acid at 60 ℃ under 0.3 MPa O2. Further characterization showed that the small size of Au clusters is the key factor for the high oxidation performance. In situ Fourier transform infrared spectroscopy revealed that glycerol was first transformed to glyceric acid, and then glyceric acid was directly oxidized to tartronic acid.
2014, 35(10): 1661-1668
doi: 10.1016/S1872-2067(14)60135-2
Abstract:
A catalyst consisting of SiO2 nanowires and highly dispersed Fe2O3 (denoted NW-FS) was synthesized in situ by iron-assisted amine-vapor-transport treatment. NW-FS was prepared by the direct transformation of an industrial spherical Fe2O3/SiO2 catalyst (denoted indus-FS). NW-FS was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, N2-sorption measurements, X-ray photoelectron spectroscopy, and temperature-programmed reduction. NW-FS exhibited a high selectivity for light olefins, especially for ethene in the Fischer-Tropsch synthesis. This was because of the highly dispersed Fe2O3 and low diffusion resistance of its open structure. The C2-C4 olefin/paraffin ratio was 3.3, which was higher than that of indus-FS at 1.9.
A catalyst consisting of SiO2 nanowires and highly dispersed Fe2O3 (denoted NW-FS) was synthesized in situ by iron-assisted amine-vapor-transport treatment. NW-FS was prepared by the direct transformation of an industrial spherical Fe2O3/SiO2 catalyst (denoted indus-FS). NW-FS was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, N2-sorption measurements, X-ray photoelectron spectroscopy, and temperature-programmed reduction. NW-FS exhibited a high selectivity for light olefins, especially for ethene in the Fischer-Tropsch synthesis. This was because of the highly dispersed Fe2O3 and low diffusion resistance of its open structure. The C2-C4 olefin/paraffin ratio was 3.3, which was higher than that of indus-FS at 1.9.
2014, 35(10): 1669-1675
doi: 10.1016/S1872-2067(14)60110-8
Abstract:
TiO2 doped with metal ions (M-TiO2, M = Zn2+, Cu2+, CO2+, Mn2+, or Ni2+) was investigated as a heterogeneous catalyst for the coupling reaction of CO2 and epoxides, using tetrabutylammonium iodide (TBAI) as a co-catalyst under solvent-free conditions. These compounds were found to exhibit high catalytic activities. The effects of reaction temperature, reaction time, and CO2 pressure on the effectiveness of a Zn-TiO2/TBAI catalyst system were also examined. Zn-TiO2 represents a nontoxic, heterogeneous catalyst that can be reutilized up to five times without a significant loss of catalytic activity.
TiO2 doped with metal ions (M-TiO2, M = Zn2+, Cu2+, CO2+, Mn2+, or Ni2+) was investigated as a heterogeneous catalyst for the coupling reaction of CO2 and epoxides, using tetrabutylammonium iodide (TBAI) as a co-catalyst under solvent-free conditions. These compounds were found to exhibit high catalytic activities. The effects of reaction temperature, reaction time, and CO2 pressure on the effectiveness of a Zn-TiO2/TBAI catalyst system were also examined. Zn-TiO2 represents a nontoxic, heterogeneous catalyst that can be reutilized up to five times without a significant loss of catalytic activity.
2014, 35(10): 1676-1686
doi: 10.1016/S1872-2067(14)60133-9
Abstract:
The SAPO-11/Beta composite molecular sieve was synthesized by the hydrothermal method with zeolite Beta as the silicon source. The physicochemical properties of SAPO-11, Beta molecular sieve, the composite molecular sieve, and the mechanical mixture of SAPO-11 and Beta molecular sieve were characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, transmission electron microscopy-energy dispersive spectroscopy, magic-angle spinning nuclear magnetic resonance, and pyridine adsorption infrared spectroscopy. In addition, the catalytic performance of platinum-loaded zeolite samples in the hydroisomerization of n-dodecane was investigated. The results indicate that the properties and catalytic performance of the composite molecular sieve were quite different from those of the pure zeolites and the mechanical mixture. Compared with the mechanical mixture, the combination of SAPO-11 and Beta by chemical bonds was more tightly bound in the composite molecular sieve with a core-shell structure. The acidity and pore structure of the composite were favorable for catalytic performance in the hydroisomerization of n-dodecane. The composite catalyst was superior to the other catalysts, especially in the yield of multibranched isomers.
The SAPO-11/Beta composite molecular sieve was synthesized by the hydrothermal method with zeolite Beta as the silicon source. The physicochemical properties of SAPO-11, Beta molecular sieve, the composite molecular sieve, and the mechanical mixture of SAPO-11 and Beta molecular sieve were characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, transmission electron microscopy-energy dispersive spectroscopy, magic-angle spinning nuclear magnetic resonance, and pyridine adsorption infrared spectroscopy. In addition, the catalytic performance of platinum-loaded zeolite samples in the hydroisomerization of n-dodecane was investigated. The results indicate that the properties and catalytic performance of the composite molecular sieve were quite different from those of the pure zeolites and the mechanical mixture. Compared with the mechanical mixture, the combination of SAPO-11 and Beta by chemical bonds was more tightly bound in the composite molecular sieve with a core-shell structure. The acidity and pore structure of the composite were favorable for catalytic performance in the hydroisomerization of n-dodecane. The composite catalyst was superior to the other catalysts, especially in the yield of multibranched isomers.
2014, 35(10): 1687-1694
doi: 10.1016/S1872-2067(14)60104-2
Abstract:
A composite Pt-based catalyst was prepared by loading MoO3 and WO3 nanoparticles onto carbon nanotubes (Pt/MoO3-WO3/CNTs). There was a uniform nanoparticle distribution with small particle sizes. This was achieved through an in situ self-assembly method using poly(diallyldimethylammo-nium chloride) as a linker and through subsequent immobilization of the Pt using ethylene glycol as a reducing agent. The total amount of oxide in the CNTs was 10 wt%, and when the molar ratio of MoO3 to WO3 was 1:0.5, Pt/MoO3-WO3/CNTs showed the highest activity for the electrocatalytic oxidation of methanol with forward peak current of 835 A/gPt. Because MoO3 and WO3 improve the electrocatalytic activity for methanol, CO oxidation ability, and the durability of the catalyst, the Pt/MoO3-WO3/CNTs catalyst exhibited excellent performance for the electrocatalytic oxidation of methanol.
A composite Pt-based catalyst was prepared by loading MoO3 and WO3 nanoparticles onto carbon nanotubes (Pt/MoO3-WO3/CNTs). There was a uniform nanoparticle distribution with small particle sizes. This was achieved through an in situ self-assembly method using poly(diallyldimethylammo-nium chloride) as a linker and through subsequent immobilization of the Pt using ethylene glycol as a reducing agent. The total amount of oxide in the CNTs was 10 wt%, and when the molar ratio of MoO3 to WO3 was 1:0.5, Pt/MoO3-WO3/CNTs showed the highest activity for the electrocatalytic oxidation of methanol with forward peak current of 835 A/gPt. Because MoO3 and WO3 improve the electrocatalytic activity for methanol, CO oxidation ability, and the durability of the catalyst, the Pt/MoO3-WO3/CNTs catalyst exhibited excellent performance for the electrocatalytic oxidation of methanol.
2014, 35(10): 1695-1700
doi: 10.1016/S1872-2067(14)60105-4
Abstract:
A water-soluble salen-Co(Ⅲ) complex was studied as catalyst for hydration of terminal alkynes to methyl ketones in the presence of H2SO4 as a co-catalyst. The products were obtained with excellent yields using relatively low catalyst loadings and a simple protocol. Notably, the products were easily separated from the catalyst after reaction by extraction, and the catalyst could be recovered and reused with only a slight loss of activity.
A water-soluble salen-Co(Ⅲ) complex was studied as catalyst for hydration of terminal alkynes to methyl ketones in the presence of H2SO4 as a co-catalyst. The products were obtained with excellent yields using relatively low catalyst loadings and a simple protocol. Notably, the products were easily separated from the catalyst after reaction by extraction, and the catalyst could be recovered and reused with only a slight loss of activity.
2014, 35(10): 1701-1708
doi: 10.1016/S1872-2067(14)60113-3
Abstract:
The novel recyclable free -ONNO-tetradentate Schiff base ligand N,N'-bis(2-hydroxy-3-methoxybenzaldehyde)4-methylbenzene-1,2-diamine (3-MOBdMBn) was synthesized. Complexation of this ligand with zinc (3-MOBdMBn-Zn) was performed, and the catalytic activity of the complex was evaluated. The polymer-supported analog of this complex (P-3-MOBdMBn-Zn) was synthesized, and its catalytic activity was studied. These free and polymer-anchored zinc complexes were prepared by the reactions of metal solutions with one molar equivalent of unsupported 3-MOBdMBn or P-3-MOBdMBn in methanol under nitrogen. The catalytic activity of 3-MOBdMBn-Zn and P-3-MOBdMBn-Zn was evaluated in phenol oxidation. The activity of P-3-MOBdMBn-Zn was significantly affected by the polymer support, and the rate of phenol conversion was around 50% for polystyrene-supported 3-MOBdMBn. The experimental results indicated that the reaction rate was affected by the polymer support, and the rate of phenol conversion was 1.64 μmol/(L·s) in the presence of polystyrene-supported 3-MOBdMBn.
The novel recyclable free -ONNO-tetradentate Schiff base ligand N,N'-bis(2-hydroxy-3-methoxybenzaldehyde)4-methylbenzene-1,2-diamine (3-MOBdMBn) was synthesized. Complexation of this ligand with zinc (3-MOBdMBn-Zn) was performed, and the catalytic activity of the complex was evaluated. The polymer-supported analog of this complex (P-3-MOBdMBn-Zn) was synthesized, and its catalytic activity was studied. These free and polymer-anchored zinc complexes were prepared by the reactions of metal solutions with one molar equivalent of unsupported 3-MOBdMBn or P-3-MOBdMBn in methanol under nitrogen. The catalytic activity of 3-MOBdMBn-Zn and P-3-MOBdMBn-Zn was evaluated in phenol oxidation. The activity of P-3-MOBdMBn-Zn was significantly affected by the polymer support, and the rate of phenol conversion was around 50% for polystyrene-supported 3-MOBdMBn. The experimental results indicated that the reaction rate was affected by the polymer support, and the rate of phenol conversion was 1.64 μmol/(L·s) in the presence of polystyrene-supported 3-MOBdMBn.
2014, 35(10): 1709-1715
doi: 10.1016/S1872-2067(14)60156-X
Abstract:
Epoxy functionalized cubic Ia3d mesoporous silica (CIMS) was successfully synthesized by epoxidizing vinyl groups prepared on the CIMS by a co-condensation method. The synthesized material was characterized by X-ray diffraction, nitrogen sorption, transmission electron microscopy, thermogravimetric analysis, and solid state 13C NMR. The vinyl groups were found to be easily epoxidized to yield epoxy functionalized CIMS. The epoxy functionalized CIMS was used as a support for the immobilization of penicillin G acylase (PGA), and the effects of the epoxy group on the initial activity and the operational stability of the immobilized PGA were studied. The results showed that the enzyme loading and initial activity of the immobilized PGA decreased with increasing amounts of epoxy groups. These observations were due to a decrease in the pore size of the mesoporous silica as well as an increase in the hydrophobicity of the silica surface. However, an appropriate amount of epoxy groups on the CIMS support was found to improve the operational stability of the immobilized PGA. This improvement was the result of increased interactions between the epoxy functionalized CIMS support and the PGA.
Epoxy functionalized cubic Ia3d mesoporous silica (CIMS) was successfully synthesized by epoxidizing vinyl groups prepared on the CIMS by a co-condensation method. The synthesized material was characterized by X-ray diffraction, nitrogen sorption, transmission electron microscopy, thermogravimetric analysis, and solid state 13C NMR. The vinyl groups were found to be easily epoxidized to yield epoxy functionalized CIMS. The epoxy functionalized CIMS was used as a support for the immobilization of penicillin G acylase (PGA), and the effects of the epoxy group on the initial activity and the operational stability of the immobilized PGA were studied. The results showed that the enzyme loading and initial activity of the immobilized PGA decreased with increasing amounts of epoxy groups. These observations were due to a decrease in the pore size of the mesoporous silica as well as an increase in the hydrophobicity of the silica surface. However, an appropriate amount of epoxy groups on the CIMS support was found to improve the operational stability of the immobilized PGA. This improvement was the result of increased interactions between the epoxy functionalized CIMS support and the PGA.
2014, 35(10): 1716-1726
doi: 10.1016/S1872-2067(14)60131-5
Abstract:
The amino-modified mesoporous material SBA-15 (NH2 -SBA-15) was prepared via co-condensation of tetraethylorthosilicate with 3-aminopropyltriethoxysilane in the presence of an amphiphilic triblock copolymer as a pore-directing agent under acidic conditions. The SBA-15-supported Cu Schiff-base complex (Cu-SBA-15) was then synthesized by condensation of salicylaldehyde with NH2-SBA-15, followed by the addition of a solution of Cu(NO3)2. The supported complex was systematically characterized by elemental analysis, inductive coupled high frequency plasma atomic emission spectrometry, powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, field scanning electron microscopy, transmission electron microscopy, N2 absorption-desorption, and thermo gravimetric analysis, and was used as the catalyst for the selective oxidation of styrene to benzaldehyde. The influence of the reaction parameters was assessed. The maximum conversion of styrene was 84.4% and the selectivity for benzaldehyde was 83.9%, when the reaction was conducted with a 2:1 molar ratio of H2O2:styrene in the presence of 3.8 wt% catalyst at 100 ℃ for 8 h. The TOF was 261.1 h-1, and the catalyst could be used three times without significant loss of activity. The uniformly sized pore channels, high specific surface area, and well-distributed active centers of the catalyst may contribute to the high activity.
The amino-modified mesoporous material SBA-15 (NH2 -SBA-15) was prepared via co-condensation of tetraethylorthosilicate with 3-aminopropyltriethoxysilane in the presence of an amphiphilic triblock copolymer as a pore-directing agent under acidic conditions. The SBA-15-supported Cu Schiff-base complex (Cu-SBA-15) was then synthesized by condensation of salicylaldehyde with NH2-SBA-15, followed by the addition of a solution of Cu(NO3)2. The supported complex was systematically characterized by elemental analysis, inductive coupled high frequency plasma atomic emission spectrometry, powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, field scanning electron microscopy, transmission electron microscopy, N2 absorption-desorption, and thermo gravimetric analysis, and was used as the catalyst for the selective oxidation of styrene to benzaldehyde. The influence of the reaction parameters was assessed. The maximum conversion of styrene was 84.4% and the selectivity for benzaldehyde was 83.9%, when the reaction was conducted with a 2:1 molar ratio of H2O2:styrene in the presence of 3.8 wt% catalyst at 100 ℃ for 8 h. The TOF was 261.1 h-1, and the catalyst could be used three times without significant loss of activity. The uniformly sized pore channels, high specific surface area, and well-distributed active centers of the catalyst may contribute to the high activity.
2014, 35(10): 1727-1739
doi: 10.1016/S1872-2067(14)60128-5
Abstract:
A new gemini surfactant, [C18H37(CH3)2-N+-(CH2)3-N+-(CH3)2C18H37]Cl2 (C18-3-18), has been successfully used as the mesopore directing agent in the hydrothermal synthesis of mesoporous ZSM-5 (MZSM-5). The synthesis of MZSM-5 was realized with a low temperature crystallization process at 130 ℃. The amount of C18-3-18 used in the synthesis affected the relative crystallinity and the textural properties of the obtained MZSM-5. Detailed investigation showed that the formation of MZSM-5 followed a crystallization transformation process. The use of C18-3-18 resulted in the formation of mesoporous material during the early stage of the synthesis, which was converted into MZSM-5 crystals templated by tetrapropylammonium bromide to form the MFI phase. As the synthesis proceeded, the MZSM-5 crystals aggregated into particles by weak interactions. This work shows that C18-3-18 can be used as a mesopore directing agent, which could provide a route for the synthesis of other mesoporous zeolites.
A new gemini surfactant, [C18H37(CH3)2-N+-(CH2)3-N+-(CH3)2C18H37]Cl2 (C18-3-18), has been successfully used as the mesopore directing agent in the hydrothermal synthesis of mesoporous ZSM-5 (MZSM-5). The synthesis of MZSM-5 was realized with a low temperature crystallization process at 130 ℃. The amount of C18-3-18 used in the synthesis affected the relative crystallinity and the textural properties of the obtained MZSM-5. Detailed investigation showed that the formation of MZSM-5 followed a crystallization transformation process. The use of C18-3-18 resulted in the formation of mesoporous material during the early stage of the synthesis, which was converted into MZSM-5 crystals templated by tetrapropylammonium bromide to form the MFI phase. As the synthesis proceeded, the MZSM-5 crystals aggregated into particles by weak interactions. This work shows that C18-3-18 can be used as a mesopore directing agent, which could provide a route for the synthesis of other mesoporous zeolites.
2014, 35(10): 1740-1751
doi: 10.1016/S1872-2067(14)60145-5
Abstract:
HZSM-5 catalysts modified with various Zn salts, namely zinc sulfate, zinc acetate, zinc nitrate, and zinc chloride, were prepared using an impregnation method. The resultant catalysts were characterized by X-ray diffraction, N2 adsorption, thermogravimetry-mass spectrometry, temperature-programmed desorption of NH3, and infrared spectroscopy using pyridine as the probe molecule. The methanol-to-aromatic (MTA) performance over the modified catalysts was investigated. The results showed that the type of Zn species in the catalyst significantly influenced the catalyst surface acidity. The distribution of acid sites and Zn species in the HZSM-5 catalyst modified with zinc sulfate effectively improved the MTA performance.
HZSM-5 catalysts modified with various Zn salts, namely zinc sulfate, zinc acetate, zinc nitrate, and zinc chloride, were prepared using an impregnation method. The resultant catalysts were characterized by X-ray diffraction, N2 adsorption, thermogravimetry-mass spectrometry, temperature-programmed desorption of NH3, and infrared spectroscopy using pyridine as the probe molecule. The methanol-to-aromatic (MTA) performance over the modified catalysts was investigated. The results showed that the type of Zn species in the catalyst significantly influenced the catalyst surface acidity. The distribution of acid sites and Zn species in the HZSM-5 catalyst modified with zinc sulfate effectively improved the MTA performance.
2014, 35(10): 1752-1760
doi: 10.1016/S1872-2067(14)60143-1
Abstract:
The effect of N2/Ar dielectric barrier discharge plasma on the photocatalytic activity of CuO/TiO2 under visible light irradiation was studied. The photocatalysts were characterized by X-ray diffraction, ultraviolet-visible spectrophotometry, transmission electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. The plasma parameters including gas composition, treatment time, and plasma power were investigated. The activities of the plasma-treated photocatalysts were evaluated by the photodegradation of methyl orange under visible light illumination. The optimal operation conditions were N2:Ar = 8:2, treatment time of 20 min, and a discharge current of 1.0 A. Simulated mercury-containing wastewater was treated by the photocatalysts.
The effect of N2/Ar dielectric barrier discharge plasma on the photocatalytic activity of CuO/TiO2 under visible light irradiation was studied. The photocatalysts were characterized by X-ray diffraction, ultraviolet-visible spectrophotometry, transmission electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. The plasma parameters including gas composition, treatment time, and plasma power were investigated. The activities of the plasma-treated photocatalysts were evaluated by the photodegradation of methyl orange under visible light illumination. The optimal operation conditions were N2:Ar = 8:2, treatment time of 20 min, and a discharge current of 1.0 A. Simulated mercury-containing wastewater was treated by the photocatalysts.
2014, 35(10): 1761-1767
doi: 10.1016/S1872-2067(14)60174-1
Abstract:
The Keplerate-type giant nanoporous isopolyoxomolybdate (NH4)42[MoVI72MoV60O372-(CH3COO)30(H2O)72], denoted {Mo132}, has been used as a catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by the one-pot, four-component thermal reaction of benzil with aromatic aldehydes, primary amines, and ammonium acetate under solvent-free conditions. The catalyst was prepared according to a previously published literature procedure using inexpensive and readily available starting materials, and subsequently characterized by FT-IR, UV and X-ray diffraction spectroscopy, as well as microanalysis. The results showed that {Mo132} exhibited high catalytic activity towards the synthesis of 1,2,4,5-tetrasubstituted imidazoles, with the desired products being formed in good to high yields. Furthermore, the catalyst was recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Overall, this new catalytic method for the synthesis of 1,2,4,5-tetrasubstituted imidazoles provides rapid access to the desired compounds following a simple work-up procedure, and avoids the use of harmful organic solvents. This method therefore represents a significant improvement over the methods currently available for the synthesis of tetrasubstituted imidazoles.
The Keplerate-type giant nanoporous isopolyoxomolybdate (NH4)42[MoVI72MoV60O372-(CH3COO)30(H2O)72], denoted {Mo132}, has been used as a catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by the one-pot, four-component thermal reaction of benzil with aromatic aldehydes, primary amines, and ammonium acetate under solvent-free conditions. The catalyst was prepared according to a previously published literature procedure using inexpensive and readily available starting materials, and subsequently characterized by FT-IR, UV and X-ray diffraction spectroscopy, as well as microanalysis. The results showed that {Mo132} exhibited high catalytic activity towards the synthesis of 1,2,4,5-tetrasubstituted imidazoles, with the desired products being formed in good to high yields. Furthermore, the catalyst was recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Overall, this new catalytic method for the synthesis of 1,2,4,5-tetrasubstituted imidazoles provides rapid access to the desired compounds following a simple work-up procedure, and avoids the use of harmful organic solvents. This method therefore represents a significant improvement over the methods currently available for the synthesis of tetrasubstituted imidazoles.
2014, 35(10): 1768-1778
doi: 10.1016/S1872-2067(14)60182-0
Abstract:
Perovskite nanocomposite catalysts LaXCoO3 (X = Mg, Ca, Sr, or Ce; n(La):n(X) = 3:2) have been prepared by a citric acid-complexing method and used for steam reforming of ethanol (SRE), leading to hydrogen generation. The samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption, and H2 temperature-programmed reduction. The effects of elemental substitution in the LaCoO3 perovskite were studied, and the catalytic performance and primary stability of the hydrogen production from SRE were investigated. In the highly substituted samples, only the Ce-doped sample was isolated as the pure perovskite phase. The presence of a Co3O4 phase in the Ca-doped or Sr-doped samples was beneficial for the reduction of the active Co component, while Sr-doped or Ce-doped samples showed good activity and stability. The sample incorporating Sr demonstrated better catalytic performance than those of other samples.
Perovskite nanocomposite catalysts LaXCoO3 (X = Mg, Ca, Sr, or Ce; n(La):n(X) = 3:2) have been prepared by a citric acid-complexing method and used for steam reforming of ethanol (SRE), leading to hydrogen generation. The samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption, and H2 temperature-programmed reduction. The effects of elemental substitution in the LaCoO3 perovskite were studied, and the catalytic performance and primary stability of the hydrogen production from SRE were investigated. In the highly substituted samples, only the Ce-doped sample was isolated as the pure perovskite phase. The presence of a Co3O4 phase in the Ca-doped or Sr-doped samples was beneficial for the reduction of the active Co component, while Sr-doped or Ce-doped samples showed good activity and stability. The sample incorporating Sr demonstrated better catalytic performance than those of other samples.
