For simulating the real deactivation of hollow titanium silicalite(HTS) zeolite in commercial ammoximation process, HTS was treated by 10% NH_3·H_2O solution at 120 ℃ in stirred autoclave. It is found that a par...For simulating the real deactivation of hollow titanium silicalite(HTS) zeolite in commercial ammoximation process, HTS was treated by 10% NH_3·H_2O solution at 120 ℃ in stirred autoclave. It is found that a part of HTS zeolite crystals dissolved in the hot NH_3·H_2O solution, and the specific surface area and pore volume continuously decreased with the increase in NH_3 hydrothermal treatment time. Meanwhile, the transformation of framework Ti species into extraframework Ti species was detected by the spectroscopic methods. However, the extraframework Ti species were still in a highly dispersed state after the hydrothermal and thermal treatments as shown by TEM images, while the formation of new acid sites was not detected. Upon combining the results of characterization with catalytic performance of HTS, the main deactivation reason for this material had been determined, which might be attributed to the reduction of specific surface area and active centers after basic treatment and calcination of HTS samples. And then the possible mechanism of simulated deactivation of HTS zeolite was proposed, which could describe the elemental reaction steps much more visually and directly.展开更多
Zeolite-encapsulated extraframework mono-/binuclear Fe3+species exhibit higher catalytic activity compared to clusters and nanoparticles for direct low-temperature alkane oxidation.However,the fine control of mono-/bi...Zeolite-encapsulated extraframework mono-/binuclear Fe3+species exhibit higher catalytic activity compared to clusters and nanoparticles for direct low-temperature alkane oxidation.However,the fine control of mono-/binuclear Fe3+in zeolites is challenging,and the reaction mechanism of low-temperature alkane oxidation remains unclear.Different from previous impregnation and ion-exchange methods generating clusters/nanoparticles,here we developed an efficient amino acid-assisted one-pot hydrothermal synthesis strategy for in situ incorporation of mono-/binuclear Fe^(3+)species into framework Al-rich ZSM-5 zeolites.The high framework Al content(Si/Al=9)provided sufficient negatively charged sites to anchor mono-/binuclear Fe^(3+)Fe loading=0.44∼0.90 wt%).The as-prepared 0.44Fe@Z-L_(0.3)H_(6)-9 catalyst exhibited superior catalytic properties for selective oxidation of both methane and ethane in the H_(2)O_(2)solution at 50℃,presenting a toplevel catalytic performance among various heterogeneous/homogeneous catalysts.Combining advanced characterizations and density functional theory calculations,the complex reaction networks for methane and ethane conversions into C1/C2 oxygenates over mononuclear and binuclear Fe^(3+)were mapped out for the first time.The mononuclear Fe^(3+)was more active than the binuclear Fe^(3+)for both methane and ethane conversions.This work not only provides a whole picture on low-temperature alkane oxidation mechanisms,but it also guides the rational design of high-performance catalysts for C-H bond activation and beyond.展开更多
In situ infrared spectra of dimethyl ether adsorbed on two H-ZSM-5 zeolites are reported which are different in both lattice and extraframework aluminium contents. A number of dissociatively adsorbed dimethyl ether sp...In situ infrared spectra of dimethyl ether adsorbed on two H-ZSM-5 zeolites are reported which are different in both lattice and extraframework aluminium contents. A number of dissociatively adsorbed dimethyl ether species associated respectively with the Bronsted acid sites, the external silanol groups and extraframework aluminium species at different temperatures are identified. In particular, dimethyl ether reacts with non acidic hydroxyl species associated with extraframework aluminium to form the third methoxy species. The distributions of hydrocarbons desorbed from a single pulse of dimethyl ether (1.0 mL) onto these zeolite samples are presented. Propene is the major product, and the yield of hydrocarbons correlates with the concentration of Bronsted acid bound methoxy groups.展开更多
基金financially supported by the National Basic Research Program of China(973 Program,2006CB202508)the China Petrochemical Corporation(SINOPEC Group 20673054)
文摘For simulating the real deactivation of hollow titanium silicalite(HTS) zeolite in commercial ammoximation process, HTS was treated by 10% NH_3·H_2O solution at 120 ℃ in stirred autoclave. It is found that a part of HTS zeolite crystals dissolved in the hot NH_3·H_2O solution, and the specific surface area and pore volume continuously decreased with the increase in NH_3 hydrothermal treatment time. Meanwhile, the transformation of framework Ti species into extraframework Ti species was detected by the spectroscopic methods. However, the extraframework Ti species were still in a highly dispersed state after the hydrothermal and thermal treatments as shown by TEM images, while the formation of new acid sites was not detected. Upon combining the results of characterization with catalytic performance of HTS, the main deactivation reason for this material had been determined, which might be attributed to the reduction of specific surface area and active centers after basic treatment and calcination of HTS samples. And then the possible mechanism of simulated deactivation of HTS zeolite was proposed, which could describe the elemental reaction steps much more visually and directly.
基金support of the National Natural Science Foundation of China(grant nos.22288101,21920102005,91961119,and 22101098)the National Key Research and Development Program of China(grant nos.2021YFA1501202 and 2022YFA1503600)the 111 Project(B17020).
文摘Zeolite-encapsulated extraframework mono-/binuclear Fe3+species exhibit higher catalytic activity compared to clusters and nanoparticles for direct low-temperature alkane oxidation.However,the fine control of mono-/binuclear Fe3+in zeolites is challenging,and the reaction mechanism of low-temperature alkane oxidation remains unclear.Different from previous impregnation and ion-exchange methods generating clusters/nanoparticles,here we developed an efficient amino acid-assisted one-pot hydrothermal synthesis strategy for in situ incorporation of mono-/binuclear Fe^(3+)species into framework Al-rich ZSM-5 zeolites.The high framework Al content(Si/Al=9)provided sufficient negatively charged sites to anchor mono-/binuclear Fe^(3+)Fe loading=0.44∼0.90 wt%).The as-prepared 0.44Fe@Z-L_(0.3)H_(6)-9 catalyst exhibited superior catalytic properties for selective oxidation of both methane and ethane in the H_(2)O_(2)solution at 50℃,presenting a toplevel catalytic performance among various heterogeneous/homogeneous catalysts.Combining advanced characterizations and density functional theory calculations,the complex reaction networks for methane and ethane conversions into C1/C2 oxygenates over mononuclear and binuclear Fe^(3+)were mapped out for the first time.The mononuclear Fe^(3+)was more active than the binuclear Fe^(3+)for both methane and ethane conversions.This work not only provides a whole picture on low-temperature alkane oxidation mechanisms,but it also guides the rational design of high-performance catalysts for C-H bond activation and beyond.
文摘In situ infrared spectra of dimethyl ether adsorbed on two H-ZSM-5 zeolites are reported which are different in both lattice and extraframework aluminium contents. A number of dissociatively adsorbed dimethyl ether species associated respectively with the Bronsted acid sites, the external silanol groups and extraframework aluminium species at different temperatures are identified. In particular, dimethyl ether reacts with non acidic hydroxyl species associated with extraframework aluminium to form the third methoxy species. The distributions of hydrocarbons desorbed from a single pulse of dimethyl ether (1.0 mL) onto these zeolite samples are presented. Propene is the major product, and the yield of hydrocarbons correlates with the concentration of Bronsted acid bound methoxy groups.
