HZSM-5 coating using three colloidal silica binders,acidic colloidal silica(ACS),neutral colloidal silica(NCS) and basic colloidal silica(BCS),was prepared to study the effect of binders on their adhesion and catalyti...HZSM-5 coating using three colloidal silica binders,acidic colloidal silica(ACS),neutral colloidal silica(NCS) and basic colloidal silica(BCS),was prepared to study the effect of binders on their adhesion and catalytic activity.Scanning electron microscopy characterization indicated that the zeolite coating using BCS shows the smoothest surface with higher homogeneity and adherence strength.The specific surface area,relative crystallization and acid site strength of zeolites are also dependent on the binder used.Catalytic cracking of supercritical ndodecane over the series of zeolite coating with various binders indicated that HZSM-5 coating with BCS exhibits the highest and the most stable catalytic activity compared with other kinds of binders,and also exhibits a stable catalytic activity ascribed to its proper acid property and microstructure.展开更多
In this study,various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5.The effects of particle size and Si/Al ratio of initia...In this study,various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5.The effects of particle size and Si/Al ratio of initial ZSM-5 zeolites on the structure and catalytic performance of ZSM-5/MCM-41 composites are studied.The results of XRD,TEM N_2-adsorption-desorption,NH_3-TPD and in situ FT-IR revealed that ordered hexagonal MCM-41 mesopores with 3-4 nm pore size were formed around ZSM-5 crystals,and the specific surface area and mesopore volume of composites increased with increasing the Si/Al ratio of initial ZSM-5.Catalytic cracking of n-dodecane(550℃,4 MPa) showed that the ZSM-5/MCM-41 composites obtained from the high Si/Al ratio and nano-sized initial ZSM-5 zeolites exhibited superior catalytic performance,with the improvement higher than 87%in the catalytic activities and 21%in the deactivation rate compared with untreated zeolites.This could be ascribed to their suitable pore structure,which enhanced the diffusion of reactant molecules in pores of catalysts.展开更多
ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction,scanning electron microscopy,nitrogen adsorption-desorption,ammo...ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction,scanning electron microscopy,nitrogen adsorption-desorption,ammonia temperature-programmed desorption and in-situ Fourier-transform infrared spectroscopy.The delamination induced a change in the morphology of ITQ-2 zeolites from aggregated thin platelets to scattered platelets,together with a significant increase in external specific surface area,which reached a plateau at the ultrasonic treatment time of 3 h.The catalytic cracking of n-dodecane over ITQ-2 zeolites was evaluated with ITQ-2 coated on the inside wall of a tubular reactor at 550 ℃ and 4 MPa.The sample obtained by ultrasonic treatment of 3 h(ITQ-2-3) gave the highest initial conversion of n-dodecane.whereas those of 5 h and 1 h gave the conversion even lower than MCM-22,which was in agreement with the trend of the ratio of strong Lewis acid to the total acid amount.Although the amount of cokes deposited on ITQ-2-3 was larger than that on MCM-22,the former deactivated slowly,suggesting that a large external specific surface area benefits the stability of zeolite coatings.展开更多
基金Supported by the National Natural Science Foundation of China(91116001)
文摘HZSM-5 coating using three colloidal silica binders,acidic colloidal silica(ACS),neutral colloidal silica(NCS) and basic colloidal silica(BCS),was prepared to study the effect of binders on their adhesion and catalytic activity.Scanning electron microscopy characterization indicated that the zeolite coating using BCS shows the smoothest surface with higher homogeneity and adherence strength.The specific surface area,relative crystallization and acid site strength of zeolites are also dependent on the binder used.Catalytic cracking of supercritical ndodecane over the series of zeolite coating with various binders indicated that HZSM-5 coating with BCS exhibits the highest and the most stable catalytic activity compared with other kinds of binders,and also exhibits a stable catalytic activity ascribed to its proper acid property and microstructure.
基金Supported by the National Natural Science Foundation of China(U123213421306132)the Doctoral Program of Higher Education(20120032120008)
文摘In this study,various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5.The effects of particle size and Si/Al ratio of initial ZSM-5 zeolites on the structure and catalytic performance of ZSM-5/MCM-41 composites are studied.The results of XRD,TEM N_2-adsorption-desorption,NH_3-TPD and in situ FT-IR revealed that ordered hexagonal MCM-41 mesopores with 3-4 nm pore size were formed around ZSM-5 crystals,and the specific surface area and mesopore volume of composites increased with increasing the Si/Al ratio of initial ZSM-5.Catalytic cracking of n-dodecane(550℃,4 MPa) showed that the ZSM-5/MCM-41 composites obtained from the high Si/Al ratio and nano-sized initial ZSM-5 zeolites exhibited superior catalytic performance,with the improvement higher than 87%in the catalytic activities and 21%in the deactivation rate compared with untreated zeolites.This could be ascribed to their suitable pore structure,which enhanced the diffusion of reactant molecules in pores of catalysts.
文摘ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction,scanning electron microscopy,nitrogen adsorption-desorption,ammonia temperature-programmed desorption and in-situ Fourier-transform infrared spectroscopy.The delamination induced a change in the morphology of ITQ-2 zeolites from aggregated thin platelets to scattered platelets,together with a significant increase in external specific surface area,which reached a plateau at the ultrasonic treatment time of 3 h.The catalytic cracking of n-dodecane over ITQ-2 zeolites was evaluated with ITQ-2 coated on the inside wall of a tubular reactor at 550 ℃ and 4 MPa.The sample obtained by ultrasonic treatment of 3 h(ITQ-2-3) gave the highest initial conversion of n-dodecane.whereas those of 5 h and 1 h gave the conversion even lower than MCM-22,which was in agreement with the trend of the ratio of strong Lewis acid to the total acid amount.Although the amount of cokes deposited on ITQ-2-3 was larger than that on MCM-22,the former deactivated slowly,suggesting that a large external specific surface area benefits the stability of zeolite coatings.
