The present study reports a novel strategy to fabricate nanocrystal-assembled hierarchical MOR zeolites. This is the first demonstration of hierarchical MOR without preferential growth along the c-axis, which facilita...The present study reports a novel strategy to fabricate nanocrystal-assembled hierarchical MOR zeolites. This is the first demonstration of hierarchical MOR without preferential growth along the c-axis, which facilitates mass transfer in the 12-membered ring channels of MOR zeolite for the conversions involving bulky molecules. The facile method involves the combined use of tetraethylammonium hydroxide （TEAOH） and commercial surfactants, in which TEAOH is essential for the construction of nanocrystal assemblies. The surfactant serves as a crystal growth-inhibiting agent to further inhibit nanocrystalline particle growth, resulting in enhanced mesoporosity. The hierarchical MOR assembled particles, constructed of 20-50-nm crystallites, exhibit superior catalytic properties in the alkylation of benzene with benzyl alcohol compared with the control sample, as the hierarchical MOR possesses a larger external surface area and longer c-axis dimension. More importantly, the material shows improved activity and stability in the dimethyl ether carbonylation to methyl acetate reaction, which is a novel route to produce ethanol from syngas.展开更多
The catalytic performance of KOH/mordenite has been studied for transesterification of palm oil using a batch reactor and a packed-bed reactor at 60 C and atmospheric pressure.The KOH/mordenite processed transesterifi...The catalytic performance of KOH/mordenite has been studied for transesterification of palm oil using a batch reactor and a packed-bed reactor at 60 C and atmospheric pressure.The KOH/mordenite processed transesterification in the batch reactor gave the highest methyl ester yield of96.7%under optimum conditions,while a methyl ester content over 94.5%was obtained in the packed-bed reactor.This comparison indicates that transesterification in a batch-type reactor gives a higher methyl ester yield than that of a continuous-flow reactor.Dealumination was found in the calcined catalysts and had a significant effect on the physical structure and chemical composition of the catalysts.Leaching of the potassium species was negligible,whereas depositing and washing of the reacted mixture with acetone on the catalyst surface were observed by FTIR.展开更多
The distribution of Fe and the adsorption of NH3 in H-[Fe]MOR （mordenite） were investigated using dispersion corrected density functional theory （DFT-D2）.Based on the results,it can be found that the most favorabl...The distribution of Fe and the adsorption of NH3 in H-[Fe]MOR （mordenite） were investigated using dispersion corrected density functional theory （DFT-D2）.Based on the results,it can be found that the most favorable site for the distribution of Fe is T1O6,followed by T2O5,T4O2 and T3O1,and energy differences for Fe in different T sites are less than 0.09 eV,indicating that Fe atoms may distribute in all kinds of T sites in MOR.In addition,the adsorption energies for NH3 at each crystallographic position of H-[Fe]MOR were also determined.Finally,it can be concluded that the Br（o）nsted acid site at T2O5 is stronger than the other acid sites,and the adsorption of NH3 on Br（o）nsted acid sites is more stable than on Lewis acid sites.展开更多
The growing consumption of light olefins has stimulated intensive researches on methanol to olefin(MTO)process which possesses great advantages for coal conversion to value‐added chemicals in an environmentally benig...The growing consumption of light olefins has stimulated intensive researches on methanol to olefin(MTO)process which possesses great advantages for coal conversion to value‐added chemicals in an environmentally benign way.The catalysts commonly used for MTO process faces several challenges such as poor selectivity control,low hydrothermal stability and short lifetime.In the present study,we prepared a series of mordenite zeolites with variable Al contents(Si/Al molar ratios of 51−436)by a sequential dealumination treatment of air‐calcination and acid leaching.The textural properties,acidity and Al location before and after the dealumination treatment have been systematically studied and their effect on MTO especially the methanol to propylene(MTP)performance was thoroughly investigated.The mordenite zeolites with the Si/Al ratios over 150 selectively catalyzed methanol conversion in the MTP pathway,providing a high propylene selectivity of 63%and propylene/ethylene ratio of>10.Compared to the low‐silica MOR catalysts,highly dealuminated MOR showed much higher stability and longer lifetime,which can be further enhanced via harsh hydrothermal pretreatment.Furthermore,the lifetime was highly related to the crystal size along c‐axis.The excellent performance of highly dealuminated MOR is likely ascribed to the mesopores formed upon dealumination and the scarce Al sites located in the T sites shared by the 8‐member ring(MR)side pockets and 12‐MR pore channels.展开更多
Silver iodide nanoclusters were successfully prepared in the channels of mordenite by a heat diffusion method. Powder X ray diffraction, adsorption technique and infrared spectroscopy were used to characterize the pr...Silver iodide nanoclusters were successfully prepared in the channels of mordenite by a heat diffusion method. Powder X ray diffraction, adsorption technique and infrared spectroscopy were used to characterize the prepared materials, which showed that the guest silver iodide had been encapsulated in the channels of mordenite. The optical properties of the solid phase diffuse reflectance absorption of nanocomposite material NaM AgI were studied, showing that the absorption bands of the diffuse reflectance absorption of the prepared material moved to the region of high energy. The absorption peak of the material prepared shifted to the region of high energy. Namely, blue shift was caused. This has demonstrated the incorporation of silver iodide into the channels of the zeolite. We observed the luminescence and surface photovoltage spectra of NaM AgI sample, proposing the mechanisms of the photoluminescence and photovoltaic responses.展开更多
The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the py...The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity（> 65.3%） of C;-C;, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30 min to more than 120 min after the modification with pyridine.1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts’ lifetime. It can be concluded from ex-situ;C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.展开更多
The aim of this work was to evaluate the catalytic properties for n-hexane isomerization of bifunctional monometallic (Ni or Pt) and bimetallic catalysts (Pt-Ni), using HMOR zeolite as support. The method used for met...The aim of this work was to evaluate the catalytic properties for n-hexane isomerization of bifunctional monometallic (Ni or Pt) and bimetallic catalysts (Pt-Ni), using HMOR zeolite as support. The method used for metal dispersion in the zeolite was competitive ion exchange using ammine complexes [Ni(NH3)6]Cl2 and [Pt(NH3)4]Cl2 as precursors. The catalysts were characterized by X-Ray diffraction, X-Ray energy dispersion spectroscopy, temperature-programmed reduction and transmission electron microscopy. The n-hexane isomerization reaction using the catalysts was carried out to evaluate the catalyst activity. The reaction was carried out in a fixed bed reactor operating at 250?C, 1 atm, H2/C6 = 9 molar ratio. The profiles obtained from TPR suggest that, for bimetallic catalysts, the presence of platinum facilitates the reduction of Ni2+ cations. The bimetallic catalysts presented a higher activity in the isomerization of n-hexane when compared to the monometallic ones, as well better stability as the Pt content in the solid increases.展开更多
The effects of RE modified mordenite catalysts on the activity and selectivity of amination reaction at atmospheric pressure in a fixed bed reactor were studied. The experimental result shows that the Y modified mor...The effects of RE modified mordenite catalysts on the activity and selectivity of amination reaction at atmospheric pressure in a fixed bed reactor were studied. The experimental result shows that the Y modified mordenite catalyst exhibits very good activity and selectivity to dimethylamine(DMA). The results of the catalyst characterization demonstrate that the rare earth modification of mordenite mainly causes the changes of B acidic sites in mordenite. The crystal structure and the Si/Al ratio on the surface of mordenite basically remain unchanged after mordenite is modified by rare earth elements. Rare earth modification improves the thermal stability and prolongs the life of the catalyst.展开更多
A preferentially oriented mordenite membrane was successfully prepared on a seeded porous α-alumina support. Characterization results of XRD (X-ray diffractometer) and FE-SEM (field emission scanning electron microsc...A preferentially oriented mordenite membrane was successfully prepared on a seeded porous α-alumina support. Characterization results of XRD (X-ray diffractometer) and FE-SEM (field emission scanning electron microscope) revealed that evolutionary selection might predominantly contribute to the formation of the sharply oriented mordenite membrane. The nec- essary conditions under which evolutionary selection occurs are: (a) the number density of nuclei on the support surface should be high enough at the early stage; (b) the crystals should grow fastest along one direction; and (c) the zeolite layer should proceed via the successive growth of the crystals nucleated on the support surface instead of the accumulation of the crystals formed in the bulk solution.展开更多
Effects of hydrochloride acid dealumination of mordenite(MOR) catalysts for the synthesis of 1-phenyl-1-xylyl ethane(PXE) were investigated. The structure and acidity of catalysts were characterized by XRD, BET, XRF, ...Effects of hydrochloride acid dealumination of mordenite(MOR) catalysts for the synthesis of 1-phenyl-1-xylyl ethane(PXE) were investigated. The structure and acidity of catalysts were characterized by XRD, BET, XRF, FT-IR, 27Al NMR and NH3-TPD techniques. The catalytic performance of the acid-treated MOR zeolites was studied through using the alkylation of o-xylene with styrene. The test results showed that the strength of remaining Br?nsted acid sites increased despite the reduction of total number of acid sites after dealumination, and the micropores of HMOR were slightly enlarged coupled with the formation of secondary mesopores. Additionally, the modified HMOR zeolites showed longer catalyst life with the styrene conversion rate retained. Among the catalysts employed in this study, the modified mordenite that was dealuminated by HCl(2 mol/L) could be used repeatedly without significant loss of activity and selectivity during six catalytic runs, which have been ascribed to its specific acidity and structural properties.展开更多
基金supported by the National Natural Science Foundation of China(21101150,21476228,21473182)~~
文摘The present study reports a novel strategy to fabricate nanocrystal-assembled hierarchical MOR zeolites. This is the first demonstration of hierarchical MOR without preferential growth along the c-axis, which facilitates mass transfer in the 12-membered ring channels of MOR zeolite for the conversions involving bulky molecules. The facile method involves the combined use of tetraethylammonium hydroxide （TEAOH） and commercial surfactants, in which TEAOH is essential for the construction of nanocrystal assemblies. The surfactant serves as a crystal growth-inhibiting agent to further inhibit nanocrystalline particle growth, resulting in enhanced mesoporosity. The hierarchical MOR assembled particles, constructed of 20-50-nm crystallites, exhibit superior catalytic properties in the alkylation of benzene with benzyl alcohol compared with the control sample, as the hierarchical MOR possesses a larger external surface area and longer c-axis dimension. More importantly, the material shows improved activity and stability in the dimethyl ether carbonylation to methyl acetate reaction, which is a novel route to produce ethanol from syngas.
基金supported financially by the National Metal and Materials Technology Center,Thailandthe Center of Excellence on Petrochemical and Materials Technology,Thailand
文摘The catalytic performance of KOH/mordenite has been studied for transesterification of palm oil using a batch reactor and a packed-bed reactor at 60 C and atmospheric pressure.The KOH/mordenite processed transesterification in the batch reactor gave the highest methyl ester yield of96.7%under optimum conditions,while a methyl ester content over 94.5%was obtained in the packed-bed reactor.This comparison indicates that transesterification in a batch-type reactor gives a higher methyl ester yield than that of a continuous-flow reactor.Dealumination was found in the calcined catalysts and had a significant effect on the physical structure and chemical composition of the catalysts.Leaching of the potassium species was negligible,whereas depositing and washing of the reacted mixture with acetone on the catalyst surface were observed by FTIR.
基金Computational Chemistry Laboratory of School of Chemical Engineering and EnvironmentNatural Science Foundationof Shanxi Province(No.2009011014)Shenzhen Strategic Emerging Industries Special Fund Program of China(No.GGJS20120619101655715)
文摘The distribution of Fe and the adsorption of NH3 in H-[Fe]MOR （mordenite） were investigated using dispersion corrected density functional theory （DFT-D2）.Based on the results,it can be found that the most favorable site for the distribution of Fe is T1O6,followed by T2O5,T4O2 and T3O1,and energy differences for Fe in different T sites are less than 0.09 eV,indicating that Fe atoms may distribute in all kinds of T sites in MOR.In addition,the adsorption energies for NH3 at each crystallographic position of H-[Fe]MOR were also determined.Finally,it can be concluded that the Br（o）nsted acid site at T2O5 is stronger than the other acid sites,and the adsorption of NH3 on Br（o）nsted acid sites is more stable than on Lewis acid sites.
文摘The growing consumption of light olefins has stimulated intensive researches on methanol to olefin(MTO)process which possesses great advantages for coal conversion to value‐added chemicals in an environmentally benign way.The catalysts commonly used for MTO process faces several challenges such as poor selectivity control,low hydrothermal stability and short lifetime.In the present study,we prepared a series of mordenite zeolites with variable Al contents(Si/Al molar ratios of 51−436)by a sequential dealumination treatment of air‐calcination and acid leaching.The textural properties,acidity and Al location before and after the dealumination treatment have been systematically studied and their effect on MTO especially the methanol to propylene(MTP)performance was thoroughly investigated.The mordenite zeolites with the Si/Al ratios over 150 selectively catalyzed methanol conversion in the MTP pathway,providing a high propylene selectivity of 63%and propylene/ethylene ratio of>10.Compared to the low‐silica MOR catalysts,highly dealuminated MOR showed much higher stability and longer lifetime,which can be further enhanced via harsh hydrothermal pretreatment.Furthermore,the lifetime was highly related to the crystal size along c‐axis.The excellent performance of highly dealuminated MOR is likely ascribed to the mesopores formed upon dealumination and the scarce Al sites located in the T sites shared by the 8‐member ring(MR)side pockets and 12‐MR pore channels.
文摘Silver iodide nanoclusters were successfully prepared in the channels of mordenite by a heat diffusion method. Powder X ray diffraction, adsorption technique and infrared spectroscopy were used to characterize the prepared materials, which showed that the guest silver iodide had been encapsulated in the channels of mordenite. The optical properties of the solid phase diffuse reflectance absorption of nanocomposite material NaM AgI were studied, showing that the absorption bands of the diffuse reflectance absorption of the prepared material moved to the region of high energy. The absorption peak of the material prepared shifted to the region of high energy. Namely, blue shift was caused. This has demonstrated the incorporation of silver iodide into the channels of the zeolite. We observed the luminescence and surface photovoltage spectra of NaM AgI sample, proposing the mechanisms of the photoluminescence and photovoltaic responses.
基金supported by the Ministry of Science and Technology of China(2012CB224806)
文摘The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity（> 65.3%） of C;-C;, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30 min to more than 120 min after the modification with pyridine.1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts’ lifetime. It can be concluded from ex-situ;C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.
基金the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico(CNPq.Brazil)and Petrobras for their financial support to this research.
文摘The aim of this work was to evaluate the catalytic properties for n-hexane isomerization of bifunctional monometallic (Ni or Pt) and bimetallic catalysts (Pt-Ni), using HMOR zeolite as support. The method used for metal dispersion in the zeolite was competitive ion exchange using ammine complexes [Ni(NH3)6]Cl2 and [Pt(NH3)4]Cl2 as precursors. The catalysts were characterized by X-Ray diffraction, X-Ray energy dispersion spectroscopy, temperature-programmed reduction and transmission electron microscopy. The n-hexane isomerization reaction using the catalysts was carried out to evaluate the catalyst activity. The reaction was carried out in a fixed bed reactor operating at 250?C, 1 atm, H2/C6 = 9 molar ratio. The profiles obtained from TPR suggest that, for bimetallic catalysts, the presence of platinum facilitates the reduction of Ni2+ cations. The bimetallic catalysts presented a higher activity in the isomerization of n-hexane when compared to the monometallic ones, as well better stability as the Pt content in the solid increases.
文摘The effects of RE modified mordenite catalysts on the activity and selectivity of amination reaction at atmospheric pressure in a fixed bed reactor were studied. The experimental result shows that the Y modified mordenite catalyst exhibits very good activity and selectivity to dimethylamine(DMA). The results of the catalyst characterization demonstrate that the rare earth modification of mordenite mainly causes the changes of B acidic sites in mordenite. The crystal structure and the Si/Al ratio on the surface of mordenite basically remain unchanged after mordenite is modified by rare earth elements. Rare earth modification improves the thermal stability and prolongs the life of the catalyst.
文摘A preferentially oriented mordenite membrane was successfully prepared on a seeded porous α-alumina support. Characterization results of XRD (X-ray diffractometer) and FE-SEM (field emission scanning electron microscope) revealed that evolutionary selection might predominantly contribute to the formation of the sharply oriented mordenite membrane. The nec- essary conditions under which evolutionary selection occurs are: (a) the number density of nuclei on the support surface should be high enough at the early stage; (b) the crystals should grow fastest along one direction; and (c) the zeolite layer should proceed via the successive growth of the crystals nucleated on the support surface instead of the accumulation of the crystals formed in the bulk solution.
基金the financial supports of the National Natural Science Foundation of China (Grant No. 21306023, 21376051, 21106017 and 51077013)the Fund Project for Transformation of Scientific and Technological Achievements of Jiangsu Province (Grant No. BA2011086)+2 种基金the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20100092120047)the Key Program for the Scientific Research Guiding Fund of Basic Scientific Research Operation Expenditure of Southeast University (Grant No. 3207043101)the Instrumental Analysis Fund of Southeast University
文摘Effects of hydrochloride acid dealumination of mordenite(MOR) catalysts for the synthesis of 1-phenyl-1-xylyl ethane(PXE) were investigated. The structure and acidity of catalysts were characterized by XRD, BET, XRF, FT-IR, 27Al NMR and NH3-TPD techniques. The catalytic performance of the acid-treated MOR zeolites was studied through using the alkylation of o-xylene with styrene. The test results showed that the strength of remaining Br?nsted acid sites increased despite the reduction of total number of acid sites after dealumination, and the micropores of HMOR were slightly enlarged coupled with the formation of secondary mesopores. Additionally, the modified HMOR zeolites showed longer catalyst life with the styrene conversion rate retained. Among the catalysts employed in this study, the modified mordenite that was dealuminated by HCl(2 mol/L) could be used repeatedly without significant loss of activity and selectivity during six catalytic runs, which have been ascribed to its specific acidity and structural properties.
