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2016 Volume 37 Issue 2
2016, 37(2): 215-217
doi: 10.1016/S1872-2067(15)61037-3
Abstract:
2016, 37(2): 218-226
doi: 10.1016/S1872-2067(15)61024-5
Abstract:
Highly dispersed metals, metal oxides and their composites on substrates have received considerable interest in catalysis and lithium-ion batteries, because of their superior properties compared with their single-component counterparts. In this review, we introduce the properties of supercritical carbon dioxide (scCO2) expanded ethanol, such as low viscosity, near-zero surface tension and high diffusivity. We discuss the deposition procedure and formation mechanism of carbon-based composites in scCO2-expanded ethanol. This method has been used to fabricate several carbon-based composites, such as metal and metal oxide composites deposited on zero-dimensional colloidal carbon, one-dimensional carbon nanotubes, two-dimensional graphene, and three-dimensional hierarchical porous carbon. These materials and their performance as anodic materials for lithium-ion batteries will also be reviewed.
Highly dispersed metals, metal oxides and their composites on substrates have received considerable interest in catalysis and lithium-ion batteries, because of their superior properties compared with their single-component counterparts. In this review, we introduce the properties of supercritical carbon dioxide (scCO2) expanded ethanol, such as low viscosity, near-zero surface tension and high diffusivity. We discuss the deposition procedure and formation mechanism of carbon-based composites in scCO2-expanded ethanol. This method has been used to fabricate several carbon-based composites, such as metal and metal oxide composites deposited on zero-dimensional colloidal carbon, one-dimensional carbon nanotubes, two-dimensional graphene, and three-dimensional hierarchical porous carbon. These materials and their performance as anodic materials for lithium-ion batteries will also be reviewed.
2016, 37(2): 227-233
doi: 10.1016/S1872-2067(15)61025-7
Abstract:
The distribution of Si atoms in the SAPO-34 framework determines its acidity and catalytic effects. This was investigated using the charge balance between the inorganic framework and trapped template ions. Three types of templates, which yielded R+, 2R+ and 2R2+ positive charges in the cages of SAPO-34, were obtained from single crystal data and they were used to direct the synthesis of SAPO-34 with different Si contents and formation of isolated Si atoms and Si islands in the lattice. The concentration limits of SiO2 in the gel for constituting isolated Si atoms were calculated and verified experimentally. Si islands, including 5-Si, 8-Si, 11-Si, 14-Si island were described on the basis of host-guest charge compensation. An overall view of the distribution of Si atoms in SAPO-34 was given and a criterion for the strength and density of acid sites in SAPO-34 for it to be an efficient catalyst for MTO was made available.
The distribution of Si atoms in the SAPO-34 framework determines its acidity and catalytic effects. This was investigated using the charge balance between the inorganic framework and trapped template ions. Three types of templates, which yielded R+, 2R+ and 2R2+ positive charges in the cages of SAPO-34, were obtained from single crystal data and they were used to direct the synthesis of SAPO-34 with different Si contents and formation of isolated Si atoms and Si islands in the lattice. The concentration limits of SiO2 in the gel for constituting isolated Si atoms were calculated and verified experimentally. Si islands, including 5-Si, 8-Si, 11-Si, 14-Si island were described on the basis of host-guest charge compensation. An overall view of the distribution of Si atoms in SAPO-34 was given and a criterion for the strength and density of acid sites in SAPO-34 for it to be an efficient catalyst for MTO was made available.
2016, 37(2): 234-239
doi: 10.1016/S1872-2067(15)60997-4
Abstract:
A series of Pd catalysts were prepared on different supports (Fe2O3, SiO2, ZnO, MgO, Al2O3, carbon, and Amberlyst-45) and used in the selective hydrogenation of phenol to cyclohexanone in water. The Amberlyst-45 supported Pd catalyst (Pd/A-45) was highly active and selective under mild conditions (40-100℃, 0.2-1 MPa), giving a selectivity of cyclohexanone higher than 89% even at complete conversion of phenol. Experiments with different Pd loadings (or different particle sizes) confirmed that the formation of cyclohexanone was a structure sensitive reaction, and Pd particles of 12-14 nm on Amberlyst-45 gave better selectivity and stability.
A series of Pd catalysts were prepared on different supports (Fe2O3, SiO2, ZnO, MgO, Al2O3, carbon, and Amberlyst-45) and used in the selective hydrogenation of phenol to cyclohexanone in water. The Amberlyst-45 supported Pd catalyst (Pd/A-45) was highly active and selective under mild conditions (40-100℃, 0.2-1 MPa), giving a selectivity of cyclohexanone higher than 89% even at complete conversion of phenol. Experiments with different Pd loadings (or different particle sizes) confirmed that the formation of cyclohexanone was a structure sensitive reaction, and Pd particles of 12-14 nm on Amberlyst-45 gave better selectivity and stability.
2016, 37(2): 240-249
doi: 10.1016/S1872-2067(15)61030-0
Abstract:
Zeolite-13X-supported Fe (Fe/zeolite-13X) catalysts with various Fe contents were prepared by the wet impregnation method. The catalysts were characterized by N2 adsorption-desorption isotherms to estimate the Brunauer-Emmett-Teller surface areas and Barrett-Joyner-Hanlenda pore size distributions. X-ray diffraction, scanning electron microscopy, temperature-programmed reduction, and temperature-programmed desorption of NH3 were used to investigate the textural properties of the Fe/zeolite-13X catalysts. Their catalytic activities were determined for the complete oxidation of 1,4-dioxane using air as the oxidant in a fixed‐bed flow reactor in the temperature range 100-400℃. The influences of various process parameters, such as reaction temperature, metal loading, and gas hourly space velocity (GHSV), on the dioxane removal efficiency by catalytic oxidation were investigated. The stability of the catalyst was tested at 400℃ by performing time-on-stream analysis for 50 h. The Fe/zeolite-13X catalyst with 6 wt% Fe exhibited the best catalytic activity among the Fe/zeolite-13X catalysts at 400℃ and a GHSV of 24000 h-1, with 97% dioxane conversion and 95% selectivity for the formation of carbon oxides (CO and CO2). Trace amounts (< 3%) of acetaldehyde, ethylene glycol monoformate, ethylene glycol diformate, 1,4-dioxane-2-ol, 1,4-dioxane-2-one, and 2-methoxy-1,3-dioxalane were also formed as degradation products. A plausible degradation mechanism is proposed based on the products identified by GC-MS analysis.
Zeolite-13X-supported Fe (Fe/zeolite-13X) catalysts with various Fe contents were prepared by the wet impregnation method. The catalysts were characterized by N2 adsorption-desorption isotherms to estimate the Brunauer-Emmett-Teller surface areas and Barrett-Joyner-Hanlenda pore size distributions. X-ray diffraction, scanning electron microscopy, temperature-programmed reduction, and temperature-programmed desorption of NH3 were used to investigate the textural properties of the Fe/zeolite-13X catalysts. Their catalytic activities were determined for the complete oxidation of 1,4-dioxane using air as the oxidant in a fixed‐bed flow reactor in the temperature range 100-400℃. The influences of various process parameters, such as reaction temperature, metal loading, and gas hourly space velocity (GHSV), on the dioxane removal efficiency by catalytic oxidation were investigated. The stability of the catalyst was tested at 400℃ by performing time-on-stream analysis for 50 h. The Fe/zeolite-13X catalyst with 6 wt% Fe exhibited the best catalytic activity among the Fe/zeolite-13X catalysts at 400℃ and a GHSV of 24000 h-1, with 97% dioxane conversion and 95% selectivity for the formation of carbon oxides (CO and CO2). Trace amounts (< 3%) of acetaldehyde, ethylene glycol monoformate, ethylene glycol diformate, 1,4-dioxane-2-ol, 1,4-dioxane-2-one, and 2-methoxy-1,3-dioxalane were also formed as degradation products. A plausible degradation mechanism is proposed based on the products identified by GC-MS analysis.
2016, 37(2): 250-257
doi: 10.1016/S1872-2067(15)61021-X
Abstract:
Novel tetra-methoxy resorcinarene tetra-hydrazide (TMRTH) has been synthesized and used as a reducing agent and a capping agent for the synthesis of water-dispersible stable palladium nanoparticles (PdNPs). The TMRTH-PdNPs were characterized by UV-Vis spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and powder X-ray diffraction. The synthesized nanoparticles are polydispersible with a size of 5 ± 2 nm and were found to be recyclable over five cycles maintaining a catalytic activity in the Suzuki-Miyuara cross-coupling reaction. The nanocatalyst was superior in catalytic performance to conventional palladium catalysts with respect to reaction time, catalyst loading and recyclability. TMRTH-PdNPs show promise for their use in biological applications as they exhibit good antibacterial activity against gram-positive bacteria.
Novel tetra-methoxy resorcinarene tetra-hydrazide (TMRTH) has been synthesized and used as a reducing agent and a capping agent for the synthesis of water-dispersible stable palladium nanoparticles (PdNPs). The TMRTH-PdNPs were characterized by UV-Vis spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and powder X-ray diffraction. The synthesized nanoparticles are polydispersible with a size of 5 ± 2 nm and were found to be recyclable over five cycles maintaining a catalytic activity in the Suzuki-Miyuara cross-coupling reaction. The nanocatalyst was superior in catalytic performance to conventional palladium catalysts with respect to reaction time, catalyst loading and recyclability. TMRTH-PdNPs show promise for their use in biological applications as they exhibit good antibacterial activity against gram-positive bacteria.
2016, 37(2): 258-267
doi: 10.1016/S1872-2067(15)61016-6
Abstract:
Al2O3-CeO2 supports containing 1-10 wt% Ce were prepared mechanochemically by milling aluminum and/or cerium nitrates with NH4HCO3. Heteropolymolybdate, (NH4)4NiMo6O24, was used as the precursor of the Ni and Mo to prepare NiMo6/Al2O3-CeO2 components in catalysts by impregnation method. The physicochemical properties of the catalysts were determined using chemical analysis, X-ray diffraction, temperature-programmed H2 reduction, temperature-programmed NH3 desorption, X-ray photoelectron spectroscopy (XPS), and the Brunauer-Emmett-Teller method. The catalyst acidity decreased with increasing Ce concentration in the support. XPS showed that the NiS/MoS ratio decreased two-fold for the Ce-modified alumina support. NiMo6/Al2O3, which had the highest acidity, showed the highest activity in hydrodesulfurization of 1-benzothiophene (normalized per weight of catalyst). The concentration of surface MoOxSy species (which is equal to the concentration of Mo5+) gradually decreased to zero for catalysts with Ce concentrations ≥ 10 wt%. However, the activities of all the catalysts prepared mechanochemically from Al2O3 and Al2O3-CeO2 supports significantly exceeded that of a reference NiMo6/Al2O3 catalyst prepared by impregnation method using the same precursor and with the same composition.
Al2O3-CeO2 supports containing 1-10 wt% Ce were prepared mechanochemically by milling aluminum and/or cerium nitrates with NH4HCO3. Heteropolymolybdate, (NH4)4NiMo6O24, was used as the precursor of the Ni and Mo to prepare NiMo6/Al2O3-CeO2 components in catalysts by impregnation method. The physicochemical properties of the catalysts were determined using chemical analysis, X-ray diffraction, temperature-programmed H2 reduction, temperature-programmed NH3 desorption, X-ray photoelectron spectroscopy (XPS), and the Brunauer-Emmett-Teller method. The catalyst acidity decreased with increasing Ce concentration in the support. XPS showed that the NiS/MoS ratio decreased two-fold for the Ce-modified alumina support. NiMo6/Al2O3, which had the highest acidity, showed the highest activity in hydrodesulfurization of 1-benzothiophene (normalized per weight of catalyst). The concentration of surface MoOxSy species (which is equal to the concentration of Mo5+) gradually decreased to zero for catalysts with Ce concentrations ≥ 10 wt%. However, the activities of all the catalysts prepared mechanochemically from Al2O3 and Al2O3-CeO2 supports significantly exceeded that of a reference NiMo6/Al2O3 catalyst prepared by impregnation method using the same precursor and with the same composition.
2016, 37(2): 268-272
doi: 10.1016/S1872-2067(15)61019-1
Abstract:
Rh/SiO2 catalysts with tethered-phosphines with different alkyl spacer lengths have been prepared, tested and characterized. Lengthening the alkyl spacer of the tethered-phosphine improved the flexibility of tethered-phospine, promoted the formation of active species and enhanced the activity of hydroformylation over other tethered-phosphine modified Rh/SiO2 catalysts.
Rh/SiO2 catalysts with tethered-phosphines with different alkyl spacer lengths have been prepared, tested and characterized. Lengthening the alkyl spacer of the tethered-phosphine improved the flexibility of tethered-phospine, promoted the formation of active species and enhanced the activity of hydroformylation over other tethered-phosphine modified Rh/SiO2 catalysts.
2016, 37(2): 273-280
doi: 10.1016/S1872-2067(15)61014-2
Abstract:
Silicoaluminophosphate (SAPO) molecular sieves doped with cobalt (Co-SAPO-5) were synthesized hydrothermally with different concentrations of Co. Each sample was characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3 (NH3-TPD), and infrared spectrascopy of adsorbed pyridine (Py-IR). The results showed that Co was highly dispersed in the Co-SAPO-5 samples. In addition, a part of the Co content had been incorporated into the SAPO-5 framework, while the remainder existed on the surface as extra-framework Co. The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample. However, the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample. As the concentration of Co increased, the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface. NH3-TPD and Py-IR results revealed that the amount of Brønsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample. These values were also higher for samples with higher Co content. The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen. When Co was added to the SAPO-5 catalyst, the catalytic activity of the Co-SAPO-5 catalysts improved. In addition, the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased. However, with a high conversion of cyclohexane (>6.30%), the total selectivity of cyclohexanone (K) and cyclohexanol (A) decreased sharply. The K/A ratio ranged from 1.15 to 2.47. The effects of reaction conditions (i.e., reaction temperature, reaction time, initial oxygen pressure, and the catalyst amount) on the performance of the Co-SAPO-5 catalysts have also been measured. Furthermore, the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.
Silicoaluminophosphate (SAPO) molecular sieves doped with cobalt (Co-SAPO-5) were synthesized hydrothermally with different concentrations of Co. Each sample was characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3 (NH3-TPD), and infrared spectrascopy of adsorbed pyridine (Py-IR). The results showed that Co was highly dispersed in the Co-SAPO-5 samples. In addition, a part of the Co content had been incorporated into the SAPO-5 framework, while the remainder existed on the surface as extra-framework Co. The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample. However, the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample. As the concentration of Co increased, the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface. NH3-TPD and Py-IR results revealed that the amount of Brønsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample. These values were also higher for samples with higher Co content. The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen. When Co was added to the SAPO-5 catalyst, the catalytic activity of the Co-SAPO-5 catalysts improved. In addition, the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased. However, with a high conversion of cyclohexane (>6.30%), the total selectivity of cyclohexanone (K) and cyclohexanol (A) decreased sharply. The K/A ratio ranged from 1.15 to 2.47. The effects of reaction conditions (i.e., reaction temperature, reaction time, initial oxygen pressure, and the catalyst amount) on the performance of the Co-SAPO-5 catalysts have also been measured. Furthermore, the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.
2016, 37(2): 281-287
doi: 10.1016/S1872-2067(15)60993-7
Abstract:
A series of CuSO4/TiO2 catalysts were prepared using a wet impregnation method. The activity of each sample in the selective catalytic reduction of NO by NH3 (NH3-SCR) was determined. The effects of SO2 and H2O, and their combined effect, on the activity were examined at 340℃ for 24 h. The catalysts were characterized using N2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of NH3 (NH3-TPD), and in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS). The CuSO4/TiO2 catalysts had good activities, with low production of N2O above 340℃. SO2 or a combination of SO2 and H2O had little effect on the activity, and H2O caused only a slight decrease in activity during the experimental period. The NH3-TPD and H2-TPR results showed that CuSO4 increased the amounts of acid sites and adsorbed oxygen on the catalyst. In situ DRIFTS showed that the NH3-SCR reaction on the CuSO4/TiO2 catalysts followed an Eley-Rideal mechanism. The reaction of gaseous NO with NH3 adsorbed on Lewis acid sites to form N2 and H2O could be the main reaction pathway, and oxygen adsorption might favor this process.
A series of CuSO4/TiO2 catalysts were prepared using a wet impregnation method. The activity of each sample in the selective catalytic reduction of NO by NH3 (NH3-SCR) was determined. The effects of SO2 and H2O, and their combined effect, on the activity were examined at 340℃ for 24 h. The catalysts were characterized using N2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of NH3 (NH3-TPD), and in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS). The CuSO4/TiO2 catalysts had good activities, with low production of N2O above 340℃. SO2 or a combination of SO2 and H2O had little effect on the activity, and H2O caused only a slight decrease in activity during the experimental period. The NH3-TPD and H2-TPR results showed that CuSO4 increased the amounts of acid sites and adsorbed oxygen on the catalyst. In situ DRIFTS showed that the NH3-SCR reaction on the CuSO4/TiO2 catalysts followed an Eley-Rideal mechanism. The reaction of gaseous NO with NH3 adsorbed on Lewis acid sites to form N2 and H2O could be the main reaction pathway, and oxygen adsorption might favor this process.
2016, 37(2): 288-299
doi: 10.1016/S1872-2067(15)60994-9
Abstract:
This paper describes the development of an integrated approach for the preparation of diverse furan derivatives from acetylenic alcohols by gold and palladium catalyzed π-activation chemistry. Notably, this new method was found to be amenable to cyclooctyl-containing substrates, which represents a significant extension to this methodology compared with our previous reports. Furthermore, this newly developed method allowed for the direct construction of cyclooctyl furans from their synthetic precursors under Sonogashira conditions. Experimental results revealed that palladium played two major functions in these reactions, including (1) an essential catalyst in the cross-coupling reaction of the substrates; and (2) facilitating the cyclization of the acetylenic alcohol intermediates through a typical π-activation process. The scope of this chemistry was highlighted by the one-pot synthesis of 3-iodofuran, which provided an opportunity for further functionalization (via coupling methods). Finally, the AuBr3 protocol was also elaborated to domino cyclization/C-H activation reactions, as well as the cyclization of acyclic precursors. Taken together, the results of this study demonstrate that gold and palladium catalysts can be used to complement each other in cyclization reactions.
This paper describes the development of an integrated approach for the preparation of diverse furan derivatives from acetylenic alcohols by gold and palladium catalyzed π-activation chemistry. Notably, this new method was found to be amenable to cyclooctyl-containing substrates, which represents a significant extension to this methodology compared with our previous reports. Furthermore, this newly developed method allowed for the direct construction of cyclooctyl furans from their synthetic precursors under Sonogashira conditions. Experimental results revealed that palladium played two major functions in these reactions, including (1) an essential catalyst in the cross-coupling reaction of the substrates; and (2) facilitating the cyclization of the acetylenic alcohol intermediates through a typical π-activation process. The scope of this chemistry was highlighted by the one-pot synthesis of 3-iodofuran, which provided an opportunity for further functionalization (via coupling methods). Finally, the AuBr3 protocol was also elaborated to domino cyclization/C-H activation reactions, as well as the cyclization of acyclic precursors. Taken together, the results of this study demonstrate that gold and palladium catalysts can be used to complement each other in cyclization reactions.
2016, 37(2): 300-307
doi: 10.1016/S1872-2067(15)60977-9
Abstract:
A series of H3PO4-modified CeO2 samples were prepared by impregnation of CeO2 with H3PO4 solution, and evaluated for the selective catalytic reduction of NOx by NH3. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption of NH3, and temperature-programmed reduction of H2. The results showed that more than 80% NO conversion was achieved in the temperature range 250-550℃ over the H3PO4-CeO2 catalyst. The enhanced catalytic performance could be ascribed to the increase in acidic strength, especially Brönsted acidity, and reduction in redox properties of the CeO2 after H3PO4 modification.
A series of H3PO4-modified CeO2 samples were prepared by impregnation of CeO2 with H3PO4 solution, and evaluated for the selective catalytic reduction of NOx by NH3. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption of NH3, and temperature-programmed reduction of H2. The results showed that more than 80% NO conversion was achieved in the temperature range 250-550℃ over the H3PO4-CeO2 catalyst. The enhanced catalytic performance could be ascribed to the increase in acidic strength, especially Brönsted acidity, and reduction in redox properties of the CeO2 after H3PO4 modification.
2016, 37(2): 308-315
doi: 10.1016/S1872-2067(15)60979-2
Abstract:
The ZSM-5 zeolite with an unusual snowflake-shaped morphology was hydrothermally synthesized for the first time, and compared with common ellipsoidal and boat-like shaped samples. These samples were characterized by N2 adsorption-desorption, X-ray fluorescence spectroscopy, scanning electron microscopy, X-ray diffraction, magic angle spinning nuclear magnetic resonance, temperature-programmed desorption of ammonia, and infrared spectroscopy of pyridine adsorption. The results suggest that the BET surface area and SiO2/Al2O3 ratio of these samples are similar, while the snowflake-shaped ZSM-5 zeolite possesses more of the (101) face, and distortion, dislocation, and asymmetry in the framework, resulting in a larger number of acid sites than the conventional samples. Catalysts for the methanol to olefin (MTO) reaction were prepared by loading Ca on the samples. The snowflake-shaped Ca/ZSM-5 zeolite exhibited excellent selectivity for total light olefin (72%) and propene (39%) in MTO. The catalytic performance influenced by the morphology can be mainly attributed to the snowflake-shaped ZSM-5 zeolite possessing distortion, dislocation, and asymmetry in the framework, and lower diffusion limitation than the conventional samples.
The ZSM-5 zeolite with an unusual snowflake-shaped morphology was hydrothermally synthesized for the first time, and compared with common ellipsoidal and boat-like shaped samples. These samples were characterized by N2 adsorption-desorption, X-ray fluorescence spectroscopy, scanning electron microscopy, X-ray diffraction, magic angle spinning nuclear magnetic resonance, temperature-programmed desorption of ammonia, and infrared spectroscopy of pyridine adsorption. The results suggest that the BET surface area and SiO2/Al2O3 ratio of these samples are similar, while the snowflake-shaped ZSM-5 zeolite possesses more of the (101) face, and distortion, dislocation, and asymmetry in the framework, resulting in a larger number of acid sites than the conventional samples. Catalysts for the methanol to olefin (MTO) reaction were prepared by loading Ca on the samples. The snowflake-shaped Ca/ZSM-5 zeolite exhibited excellent selectivity for total light olefin (72%) and propene (39%) in MTO. The catalytic performance influenced by the morphology can be mainly attributed to the snowflake-shaped ZSM-5 zeolite possessing distortion, dislocation, and asymmetry in the framework, and lower diffusion limitation than the conventional samples.
2016, 37(2): 316-323
doi: 10.1016/S1872-2067(15)60975-5
Abstract:
A series of zeolites, including USY zeolites without sodium, Na-USY at different Na contents, La-USY with different rare earth (RE) contents and La-Na-USY with RE and Na were prepared by an ion exchange method. They were investigated to understand the activation barriers for the destruction of Y zeolite structure under hydrothermal treatment and the effect of V using the solid-state kinetic model. The results showed that the pathways for Y zeolite destruction were dealumination, desiliconization and the disappearance of La-O bonds. Zeolites were destroyed by steam through acid hydrolysis, which was accelerated by V. In addition, Na and V exerted a synergistic effect on the framework destruction, and the formation of NaOH was the rate-determining step. The presence of RE elements decreased hydrolysis and stabilized the structure of the zeolites. The interaction between V and RE destroyed zeolite structure by eliminating the stabilizing La-O [RE-OH-RE]5+ bridges in the sodalite cages.
A series of zeolites, including USY zeolites without sodium, Na-USY at different Na contents, La-USY with different rare earth (RE) contents and La-Na-USY with RE and Na were prepared by an ion exchange method. They were investigated to understand the activation barriers for the destruction of Y zeolite structure under hydrothermal treatment and the effect of V using the solid-state kinetic model. The results showed that the pathways for Y zeolite destruction were dealumination, desiliconization and the disappearance of La-O bonds. Zeolites were destroyed by steam through acid hydrolysis, which was accelerated by V. In addition, Na and V exerted a synergistic effect on the framework destruction, and the formation of NaOH was the rate-determining step. The presence of RE elements decreased hydrolysis and stabilized the structure of the zeolites. The interaction between V and RE destroyed zeolite structure by eliminating the stabilizing La-O [RE-OH-RE]5+ bridges in the sodalite cages.
