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2015 Volume 36 Issue 6
2015, 36(6):
Abstract:
2015, 36(6): 787-788
doi: 10.1016/S1872-2067(15)60876-2
Abstract:
2015, 36(6): 789-796
doi: 10.1016/S1872-2067(14)60290-4
Abstract:
Zeolites are widely used as ion exchangers, adsorbents and catalysts in the chemical and petrochemical industries because of their pore structure and acidity. Solid state NMR is a powerful tool for the characterization of the topological structure, active sites (acid sites) and host-guest interaction in zeolites. Recent advances in the solid state NMR characterization of zeolites are briefly reviewed.
Zeolites are widely used as ion exchangers, adsorbents and catalysts in the chemical and petrochemical industries because of their pore structure and acidity. Solid state NMR is a powerful tool for the characterization of the topological structure, active sites (acid sites) and host-guest interaction in zeolites. Recent advances in the solid state NMR characterization of zeolites are briefly reviewed.
2015, 36(6): 797-800
doi: 10.1016/S1872-2067(14)60285-0
Abstract:
SAPO-5 crystals with plate-like morphology were synthesized in the presence of surfactants such as cetyltrimethyl ammonium bromide under solvent-free conditions. X-ray diffraction patterns and scanning electron microscopy images revealed that the samples had high crystallinity and controllable plate-like morphology. The amount of surfactant added played an important role in controlling the thickness of the zeolite crystals. Considering the unique one-dimensional microporous architecture of AFI, SAPO-5 crystals with unique plate-like morphology are expected to be of great importance in catalytic applications.
SAPO-5 crystals with plate-like morphology were synthesized in the presence of surfactants such as cetyltrimethyl ammonium bromide under solvent-free conditions. X-ray diffraction patterns and scanning electron microscopy images revealed that the samples had high crystallinity and controllable plate-like morphology. The amount of surfactant added played an important role in controlling the thickness of the zeolite crystals. Considering the unique one-dimensional microporous architecture of AFI, SAPO-5 crystals with unique plate-like morphology are expected to be of great importance in catalytic applications.
2015, 36(6): 801-805
doi: 10.1016/S1872-2067(14)60277-1
Abstract:
Ce(IV)-containing zeolite Beta was successfully prepared by a reproducible and scalable two-step post-synthesis strategy. This consists of creating vacant T sites that are associated with silanol groups by the dealumination of the H-Beta zeolite and a subsequent dry impregnation of the resultant Si-Beta zeolite with cerium (IV) isopropoxide. XRD, FT-IR, UV-Vis and 1H MAS NMR confirmed that Ce(IV) was successfully incorporated into the Beta zeolite framework by the post-synthesis procedures and that they exist as isolated atoms with tetrahedral coordination. The mechanism of Ce incorporation into the framework of Beta zeolite was confirmed by DRIFT spectroscopy. The ring-opening hydration of epoxides to their corresponding 1,2-diols was selected as a model reaction for an evaluation of the catalytic performance of the as-synthesized Ce-Beta zeolite.
Ce(IV)-containing zeolite Beta was successfully prepared by a reproducible and scalable two-step post-synthesis strategy. This consists of creating vacant T sites that are associated with silanol groups by the dealumination of the H-Beta zeolite and a subsequent dry impregnation of the resultant Si-Beta zeolite with cerium (IV) isopropoxide. XRD, FT-IR, UV-Vis and 1H MAS NMR confirmed that Ce(IV) was successfully incorporated into the Beta zeolite framework by the post-synthesis procedures and that they exist as isolated atoms with tetrahedral coordination. The mechanism of Ce incorporation into the framework of Beta zeolite was confirmed by DRIFT spectroscopy. The ring-opening hydration of epoxides to their corresponding 1,2-diols was selected as a model reaction for an evaluation of the catalytic performance of the as-synthesized Ce-Beta zeolite.
2015, 36(6): 806-812
doi: 10.1016/S1872-2067(14)60311-9
Abstract:
Three proton-type ZSM-5 zeolites with different SiO2/Al2O3 ratios (SARs) of 33, 266, and 487 were characterized and examined as fluid catalytic cracking catalyst additives for residue oil cracking. The catalytic performance of the ZSM-5 additives was evaluated using an ultra-stable Y-zeolite (USY)-based fluid catalytic cracking catalyst in a fixed fluid bed unit. As observed, the cracking of primary olefins over the hybrid catalysts consisting of USY-based catalyst and ZSM-5 additive was considerably inhibited by increasing the SAR of the ZSM-5 zeolite, thus avoiding substantial loss of gasoline paraffins. The introduction of ZSM-5 additives led to higher liquid petroleum gas yields as well as higher isobutane and isopentane yields. The improved yields were attributed to the combined effects of the ZSM-5 additives and USY-based catalyst. The variations of gasoline paraffins and aromatics both accounted for the enhancement in the octane number values. The use of ZSM-5 with higher SARs (266 and 487) led to an enhancement in the octane number with minimal loss of gasoline. This enhancement was mainly attributed to the moderate aromatization and isomerization reactivity of the ZSM-5 additives that mainly originated from their relatively small pores and suitable acidic properties with higher SARs.
Three proton-type ZSM-5 zeolites with different SiO2/Al2O3 ratios (SARs) of 33, 266, and 487 were characterized and examined as fluid catalytic cracking catalyst additives for residue oil cracking. The catalytic performance of the ZSM-5 additives was evaluated using an ultra-stable Y-zeolite (USY)-based fluid catalytic cracking catalyst in a fixed fluid bed unit. As observed, the cracking of primary olefins over the hybrid catalysts consisting of USY-based catalyst and ZSM-5 additive was considerably inhibited by increasing the SAR of the ZSM-5 zeolite, thus avoiding substantial loss of gasoline paraffins. The introduction of ZSM-5 additives led to higher liquid petroleum gas yields as well as higher isobutane and isopentane yields. The improved yields were attributed to the combined effects of the ZSM-5 additives and USY-based catalyst. The variations of gasoline paraffins and aromatics both accounted for the enhancement in the octane number values. The use of ZSM-5 with higher SARs (266 and 487) led to an enhancement in the octane number with minimal loss of gasoline. This enhancement was mainly attributed to the moderate aromatization and isomerization reactivity of the ZSM-5 additives that mainly originated from their relatively small pores and suitable acidic properties with higher SARs.
2015, 36(6): 813-819
doi: 10.1016/S1872-2067(14)60296-5
Abstract:
Phenylene-gallosilicates were prepared with the same crystalline structure as their aluminum analogues. The new Ga-Eni Carbon Silicates (Ga-ECS) phases were investigated by X-ray diffraction, scanning electron microscopy, nuclear magnetic resonance and thermogravimetric analysis, which demonstrated that gallium isomorphously replaced aluminum in the framework of the organic-inorganic hybrids similar to the case of classical zeolites. Hybrid ECS materials were obtained with different types of bridged silsesquioxane precursors that maintained the aluminum-silicate nature of the inorganic moiety. This work confirms a new level of crystal chemistry versatility for this class of materials, and demonstrates the possibility to tailor also the inorganic part of the framework by changing the nature of the trivalent heteroatom.
Phenylene-gallosilicates were prepared with the same crystalline structure as their aluminum analogues. The new Ga-Eni Carbon Silicates (Ga-ECS) phases were investigated by X-ray diffraction, scanning electron microscopy, nuclear magnetic resonance and thermogravimetric analysis, which demonstrated that gallium isomorphously replaced aluminum in the framework of the organic-inorganic hybrids similar to the case of classical zeolites. Hybrid ECS materials were obtained with different types of bridged silsesquioxane precursors that maintained the aluminum-silicate nature of the inorganic moiety. This work confirms a new level of crystal chemistry versatility for this class of materials, and demonstrates the possibility to tailor also the inorganic part of the framework by changing the nature of the trivalent heteroatom.
2015, 36(6): 820-828
doi: 10.1016/S1872-2067(14)60287-4
Abstract:
The one-pot synthesis of 5-hydroxymethylfurfural (5-HMF) from glucose was investigated, using [Sn,Al]-Beta catalysts prepared by a combination of partial dealumination and isomorphous substitution of Sn into the zeolite framework. The amount of Al in [Sn,Al]-Beta was adjusted by changing the concentration and acid treatment time, and the Sn content was varied by changing the SnCl4 vapor treatment time. [Sn,Al]-Beta contains framework Al-related Brönsted acid sites and tetrahedral Sn-related Lewis acid sites, and is therefore a bifunctional solid acid catalyst. The reaction parameters for the [Sn,Al]-Beta-catalyzed one-pot conversion of glucose to 5-HMF were optimized. [Sn,Al]-Beta with a suitable Sn/Al molar ratio gave a glucose conversion of 60.0% and 5-HMF selectivity of 62.1%.
The one-pot synthesis of 5-hydroxymethylfurfural (5-HMF) from glucose was investigated, using [Sn,Al]-Beta catalysts prepared by a combination of partial dealumination and isomorphous substitution of Sn into the zeolite framework. The amount of Al in [Sn,Al]-Beta was adjusted by changing the concentration and acid treatment time, and the Sn content was varied by changing the SnCl4 vapor treatment time. [Sn,Al]-Beta contains framework Al-related Brönsted acid sites and tetrahedral Sn-related Lewis acid sites, and is therefore a bifunctional solid acid catalyst. The reaction parameters for the [Sn,Al]-Beta-catalyzed one-pot conversion of glucose to 5-HMF were optimized. [Sn,Al]-Beta with a suitable Sn/Al molar ratio gave a glucose conversion of 60.0% and 5-HMF selectivity of 62.1%.
2015, 36(6): 829-837
doi: 10.1016/S1872-2067(14)60301-6
Abstract:
The effect of Mo/HZSM-5 pretreatment at 973 K in inert (He), oxidizing (artificial air), and carburizing (CH4/He mixture) atmospheres on its performance in non-oxidative methane dehydroaromatization (MDA) was investigated. The effect of post-synthesis silylation on deactivation of external acid sites was also studied. Precarburization resulted in increased aromatic selectivity and improved catalyst stability. The benzene selectivity was the highest for the silylated Mo/HZSM-5 catalyst (benzene + naphthalene selectivity after 1 h on stream was close to 100%). The deactivation of precarburized zeolites was less pronounced than that of zeolites heated in air or He. During heating in air or He, larger fractions of the molybdenum oxide species diffused into the micropores than during heating in methane. Carburization of the molybdenum oxide species in the micropores during MDA resulted in the formation of molybdenum carbide particles, and these contributed to pore blocking, making the Brønsted acid sites inaccessible. The formation of molybdenum carbides during heating in methane resulted in a less mobile Mo phase. It is argued that the presence of molybdenum carbide particles in the micropores contributes to rapid catalyst deactivation, in addition to the formation of hard coke on the external surface.
The effect of Mo/HZSM-5 pretreatment at 973 K in inert (He), oxidizing (artificial air), and carburizing (CH4/He mixture) atmospheres on its performance in non-oxidative methane dehydroaromatization (MDA) was investigated. The effect of post-synthesis silylation on deactivation of external acid sites was also studied. Precarburization resulted in increased aromatic selectivity and improved catalyst stability. The benzene selectivity was the highest for the silylated Mo/HZSM-5 catalyst (benzene + naphthalene selectivity after 1 h on stream was close to 100%). The deactivation of precarburized zeolites was less pronounced than that of zeolites heated in air or He. During heating in air or He, larger fractions of the molybdenum oxide species diffused into the micropores than during heating in methane. Carburization of the molybdenum oxide species in the micropores during MDA resulted in the formation of molybdenum carbide particles, and these contributed to pore blocking, making the Brønsted acid sites inaccessible. The formation of molybdenum carbides during heating in methane resulted in a less mobile Mo phase. It is argued that the presence of molybdenum carbide particles in the micropores contributes to rapid catalyst deactivation, in addition to the formation of hard coke on the external surface.
2015, 36(6): 838-844
doi: 10.1016/S1872-2067(14)60255-2
Abstract:
A series of ordered mesoporous silicalite-1 zeolites has been synthesized by the self-assembly of nanosized zeolite silicalite-1 seeds with different sizes using a two-step procedure. The nanosized silicalite-1 seeds were prepared with an alkali precursor solution that was heated for different periods, and then assembled into ordered mesoporous materials under strongly acidic conditions, similar to that of mesoporous silica SBA-15 which has well ordered hexagonal mesopores and amorphous walls. A significant change in synthesis conditions prevents the continued growth of zeolite seeds and induces assemblage into ordered mesoporous materials templated by triblock copolymers. The samples assembled by zeolite nanoclusters were investigated by X-ray diffraction, electron microscopy, infrared spectroscopy, and N2 adsorption-desorption isotherms. This "bottom-up" approach yields porous materials that contain ordered micro- and mesopores. The mesoporous zeolite has a large surface area (> 730 m2/g).
A series of ordered mesoporous silicalite-1 zeolites has been synthesized by the self-assembly of nanosized zeolite silicalite-1 seeds with different sizes using a two-step procedure. The nanosized silicalite-1 seeds were prepared with an alkali precursor solution that was heated for different periods, and then assembled into ordered mesoporous materials under strongly acidic conditions, similar to that of mesoporous silica SBA-15 which has well ordered hexagonal mesopores and amorphous walls. A significant change in synthesis conditions prevents the continued growth of zeolite seeds and induces assemblage into ordered mesoporous materials templated by triblock copolymers. The samples assembled by zeolite nanoclusters were investigated by X-ray diffraction, electron microscopy, infrared spectroscopy, and N2 adsorption-desorption isotherms. This "bottom-up" approach yields porous materials that contain ordered micro- and mesopores. The mesoporous zeolite has a large surface area (> 730 m2/g).
2015, 36(6): 845-854
doi: 10.1016/S1872-2067(15)60859-2
Abstract:
The reaction mechanism of the oxidation of cyclohexanone catalyzed by titanium silicate zeolite TS-1 using aqueous H2O2 as the oxidant was investigated by combining density function theory (DFT) calculations with experimental studies. DFT calculations showed that H2O2 was adsorbed and activated at the tetrahedral Ti sites. By taking into account the adsorption energy, molecular size, steric hindrance and structural information, a reaction mechanism of Baeyer-Villiger oxidation catalyzed by TS-1 that involves the activation of H2O2 was proposed. Experimental studies showed that the major products of cyclohexanone oxidation by H2O2 catalyzed by a hollow TS-1 zeolite were ε-carprolactone, 6-hydroxyhexanoic acid, and adipic acid. These products were analyzed by GC-MS and were in good agreement with the proposed mechanism. Our studies showed that the reaction mechanism on TS-1 zeolite was different from that on Sn-beta zeolite.
The reaction mechanism of the oxidation of cyclohexanone catalyzed by titanium silicate zeolite TS-1 using aqueous H2O2 as the oxidant was investigated by combining density function theory (DFT) calculations with experimental studies. DFT calculations showed that H2O2 was adsorbed and activated at the tetrahedral Ti sites. By taking into account the adsorption energy, molecular size, steric hindrance and structural information, a reaction mechanism of Baeyer-Villiger oxidation catalyzed by TS-1 that involves the activation of H2O2 was proposed. Experimental studies showed that the major products of cyclohexanone oxidation by H2O2 catalyzed by a hollow TS-1 zeolite were ε-carprolactone, 6-hydroxyhexanoic acid, and adipic acid. These products were analyzed by GC-MS and were in good agreement with the proposed mechanism. Our studies showed that the reaction mechanism on TS-1 zeolite was different from that on Sn-beta zeolite.
2015, 36(6): 855-865
doi: 10.1016/S1872-2067(14)60278-3
Abstract:
A cooling-induced crystallization process was used to synthesize sod (RCSR symbol)- and zni (RCSR symbol)-type zeolitic imidazolate frameworks (ZIFs) ionothermally in 1-ethyl-3-methylimidazolium bromide ionic liquid and a urea-choline chloride deep eutectic solvent. The products were characterized by X-ray diffraction, scanning electron microscopy, nuclear magnetic resonance spectroscopy, infrared spectroscopy and thermal gravimetric analysis. The effect of the synthesis conditions on the crystallinity, size and morphology of the product was studied. The dissolution-crystallization mechanism of ZIFs was discussed. The cooling rate affected the product morphology. When the synthesis solution was cooled by rapid cooling, the shape of the sod-type product was spherical and the morphology of the zni-type product was rod-like or plate-like. With a programmed cooling, the sod-type product was polyhedron in shape and the zni-type product was in the form of clusters.
A cooling-induced crystallization process was used to synthesize sod (RCSR symbol)- and zni (RCSR symbol)-type zeolitic imidazolate frameworks (ZIFs) ionothermally in 1-ethyl-3-methylimidazolium bromide ionic liquid and a urea-choline chloride deep eutectic solvent. The products were characterized by X-ray diffraction, scanning electron microscopy, nuclear magnetic resonance spectroscopy, infrared spectroscopy and thermal gravimetric analysis. The effect of the synthesis conditions on the crystallinity, size and morphology of the product was studied. The dissolution-crystallization mechanism of ZIFs was discussed. The cooling rate affected the product morphology. When the synthesis solution was cooled by rapid cooling, the shape of the sod-type product was spherical and the morphology of the zni-type product was rod-like or plate-like. With a programmed cooling, the sod-type product was polyhedron in shape and the zni-type product was in the form of clusters.
2015, 36(6): 866-873
doi: 10.1016/S1872-2067(14)60263-1
Abstract:
An easy one-step hydrothermal process has been developed for the first time for the synthesis of hierarchically structured zeolites (HSZs) using a single micropore template of tetrapropylammonium hydroxide. Compared with conventional constructive dual-templating synthesis and destructive post-demetallation methods, this two-in-one process reduces the mass of porogens required and consequent air pollution by combustion of the template, and simplifies the synthesis. The resultant HSZs were characterized by X-ray diffraction, N2 adsorption, scanning electron microscopy, transmission electron microscopy, X-ray fluorescence, 27Al nuclear magnetic resonance, and NH3 temperature programmed desorption. The resultant HSZs with uniform shuttle-type morphology showed high hydrothermal stability and excellent catalytic activity with prolonged life-time in the model reaction of 1,3,5- triisopropylbenzene cracking. A "nucleation/growth-demetallation/recrystallization" mechanism was proposed, which is featured with the integration of zeolite crystallization/growth and basic etching into one hydrothermal process for HSZs production.
An easy one-step hydrothermal process has been developed for the first time for the synthesis of hierarchically structured zeolites (HSZs) using a single micropore template of tetrapropylammonium hydroxide. Compared with conventional constructive dual-templating synthesis and destructive post-demetallation methods, this two-in-one process reduces the mass of porogens required and consequent air pollution by combustion of the template, and simplifies the synthesis. The resultant HSZs were characterized by X-ray diffraction, N2 adsorption, scanning electron microscopy, transmission electron microscopy, X-ray fluorescence, 27Al nuclear magnetic resonance, and NH3 temperature programmed desorption. The resultant HSZs with uniform shuttle-type morphology showed high hydrothermal stability and excellent catalytic activity with prolonged life-time in the model reaction of 1,3,5- triisopropylbenzene cracking. A "nucleation/growth-demetallation/recrystallization" mechanism was proposed, which is featured with the integration of zeolite crystallization/growth and basic etching into one hydrothermal process for HSZs production.
2015, 36(6): 874-879
doi: 10.1016/S1872-2067(14)60306-5
Abstract:
Phase pure AlPO4 with the AlPO4-18 (AEI) structure was synthesised using N,N- diisopropylethylamine as a template. Using a combination of X-ray powder diffraction and computational methods, the location and orientation of the N,N-diisopropylethylamine molecules inside the cages of the AEI structure were determined. Thermogravimetric analysis confirmed that the number of template molecules per unit cell was consistent with the diffraction study. We unequivocally show that only one template molecule is present in each cage of the crystalline AEI material. Our work demonstrates that a combined approach enables accurate structure resolution of such complex materials.
Phase pure AlPO4 with the AlPO4-18 (AEI) structure was synthesised using N,N- diisopropylethylamine as a template. Using a combination of X-ray powder diffraction and computational methods, the location and orientation of the N,N-diisopropylethylamine molecules inside the cages of the AEI structure were determined. Thermogravimetric analysis confirmed that the number of template molecules per unit cell was consistent with the diffraction study. We unequivocally show that only one template molecule is present in each cage of the crystalline AEI material. Our work demonstrates that a combined approach enables accurate structure resolution of such complex materials.
2015, 36(6): 880-888
doi: 10.1016/S1872-2067(14)60289-8
Abstract:
Zn-containing HZSM-5 zeolites with different Zn contents were prepared by ion exchange and physically mixing methods, and were characterized by X-ray diffraction, scanning electron microscope, N2 adsorption-desorption, NH3 temperature programmed desorption, pyridine adsorption infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Zn species introduced into HZSM-5 were identified as ZnO crystals, ZnO clusters in the zeolite channel and Zn(OH)+ species formed from a solid state reaction between dispersed ZnO and the protons in the zeolite. The preparation method has a significant influence on the distribution of the Zn species. The catalytic behavior of Zn-containing HZSM-5 with different Zn contents showed that the Zn(OH)+ and ZnO species were responsible for aromatic formation from ethylene.
Zn-containing HZSM-5 zeolites with different Zn contents were prepared by ion exchange and physically mixing methods, and were characterized by X-ray diffraction, scanning electron microscope, N2 adsorption-desorption, NH3 temperature programmed desorption, pyridine adsorption infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Zn species introduced into HZSM-5 were identified as ZnO crystals, ZnO clusters in the zeolite channel and Zn(OH)+ species formed from a solid state reaction between dispersed ZnO and the protons in the zeolite. The preparation method has a significant influence on the distribution of the Zn species. The catalytic behavior of Zn-containing HZSM-5 with different Zn contents showed that the Zn(OH)+ and ZnO species were responsible for aromatic formation from ethylene.
2015, 36(6): 889-896
doi: 10.1016/S1872-2067(14)60300-4
Abstract:
Using tetraethylammonium hydroxide as the organic structure-directing agent and in the presence of fluoride, polymorph A-enriched silica beta zeolite was synthesized under concentrated hydrothermal conditions. The introduction of Al species into the same starting mixture resulted in a decrease in the degree of enrichment of polymorph A in beta zeolite and an Al-incorporated beta zeolite resulted. The crystallized polymorph A-enriched silica beta zeolite and the Al-incorporated beta zeolite and their crystallization processes were investigated by X-ray diffractometry, elemental analysis, thermogravimetric analysis-differential thermal analysis, nitrogen adsorption, scanning electron microscopy, and solid-state magic angle spinning nuclear magnetic resonance. The introduction of Al species accelerated crystallization and reduced the crystal size of Al-incorporated beta zeolite. The intermediate of five-coordinated Al species accounted for a decrease in the degree of enrichment of polymorph A in the crystallization of Al-incorporated beta zeolite.
Using tetraethylammonium hydroxide as the organic structure-directing agent and in the presence of fluoride, polymorph A-enriched silica beta zeolite was synthesized under concentrated hydrothermal conditions. The introduction of Al species into the same starting mixture resulted in a decrease in the degree of enrichment of polymorph A in beta zeolite and an Al-incorporated beta zeolite resulted. The crystallized polymorph A-enriched silica beta zeolite and the Al-incorporated beta zeolite and their crystallization processes were investigated by X-ray diffractometry, elemental analysis, thermogravimetric analysis-differential thermal analysis, nitrogen adsorption, scanning electron microscopy, and solid-state magic angle spinning nuclear magnetic resonance. The introduction of Al species accelerated crystallization and reduced the crystal size of Al-incorporated beta zeolite. The intermediate of five-coordinated Al species accounted for a decrease in the degree of enrichment of polymorph A in the crystallization of Al-incorporated beta zeolite.
2015, 36(6): 897-905
doi: 10.1016/S1872-2067(15)60864-6
Abstract:
Pristine ETS-10 and AM-6 and their Co2+-exchanged forms were prepared, and their catalytic activities toward the oxidation of styrene in oxygen atmosphere were studied in dimethylformamide. The catalysts were denoted as Co-E10-n (n = 0, 9, 26, 68, 81) and Co-A6-m (m = 0, 8, 23, 63, 79), where n and m denote the degree of Co2+ exchange. The products of the oxidation process were identified as styrene epoxide (E) and benzaldehyde (B). Both the pristine forms, ETS-10 (Co-E10-0) and AM-6 (Co-A6-0), and Co2+-exchanged forms displayed catalytic activities. With increasing n or m, the conversion, and hence the rate, increased. Specifically, the rates varied from 6.1 to 12.5 mmol·g-1·h-1 with increasing n (Co-E10-n catalysts) and from 5.4 to 12.4 mmol·g-1·h-1 with increasing m (Co-A6-m catalysts). In contrast, the E/B ratio decreased with increasing n or m. More specifically, the E/B ratio decreased from 2.1 to 0.1 with increasing n from 0 to 81 (Co-E10-n catalysts) and from 1.3 to 0.1 with increasing m from 0 to 79 (Co-A6-m catalysts). Co-E10-9 displayed the highest E yield and Co-A6-79 generated the highest B yield. The highest turnover frequency obtained was 36.3 Co-1·h-1, which was the highest one obtained among those obtained for the Co2+-exchanged zeolites and mesoporous silica reference materials studied in this work.
Pristine ETS-10 and AM-6 and their Co2+-exchanged forms were prepared, and their catalytic activities toward the oxidation of styrene in oxygen atmosphere were studied in dimethylformamide. The catalysts were denoted as Co-E10-n (n = 0, 9, 26, 68, 81) and Co-A6-m (m = 0, 8, 23, 63, 79), where n and m denote the degree of Co2+ exchange. The products of the oxidation process were identified as styrene epoxide (E) and benzaldehyde (B). Both the pristine forms, ETS-10 (Co-E10-0) and AM-6 (Co-A6-0), and Co2+-exchanged forms displayed catalytic activities. With increasing n or m, the conversion, and hence the rate, increased. Specifically, the rates varied from 6.1 to 12.5 mmol·g-1·h-1 with increasing n (Co-E10-n catalysts) and from 5.4 to 12.4 mmol·g-1·h-1 with increasing m (Co-A6-m catalysts). In contrast, the E/B ratio decreased with increasing n or m. More specifically, the E/B ratio decreased from 2.1 to 0.1 with increasing n from 0 to 81 (Co-E10-n catalysts) and from 1.3 to 0.1 with increasing m from 0 to 79 (Co-A6-m catalysts). Co-E10-9 displayed the highest E yield and Co-A6-79 generated the highest B yield. The highest turnover frequency obtained was 36.3 Co-1·h-1, which was the highest one obtained among those obtained for the Co2+-exchanged zeolites and mesoporous silica reference materials studied in this work.
2015, 36(6): 906-912
doi: 10.1016/S1872-2067(14)60267-9
Abstract:
Hierarchically structured Ti-β zeolites were prepared using a two-step post-synthesis approach. The physicochemical properties of the resultant Ti-mβ-Sx materials were determined using various techniques, including X-ray diffraction, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, and ultraviolet-visible and ultraviolet-Raman spectroscopies. The porous structures of the synthesized hierarchical Ti-β zeolites were well preserved. Their catalytic performance was compared with that of pure microporous Ti-β materials using alkene epoxidation as a model reaction. It was found that although comparable catalytic activities were obtained for both types of catalyst in the epoxidation of small molecules, e.g., cyclohexene, the synthesized hierarchical Ti-β gave an enhanced catalytic performance in the epoxidation of bulky 1-dodecene.
Hierarchically structured Ti-β zeolites were prepared using a two-step post-synthesis approach. The physicochemical properties of the resultant Ti-mβ-Sx materials were determined using various techniques, including X-ray diffraction, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, and ultraviolet-visible and ultraviolet-Raman spectroscopies. The porous structures of the synthesized hierarchical Ti-β zeolites were well preserved. Their catalytic performance was compared with that of pure microporous Ti-β materials using alkene epoxidation as a model reaction. It was found that although comparable catalytic activities were obtained for both types of catalyst in the epoxidation of small molecules, e.g., cyclohexene, the synthesized hierarchical Ti-β gave an enhanced catalytic performance in the epoxidation of bulky 1-dodecene.
