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
Using silica gel as the precursor, MCM-22(p) was synthesized under the static conditions. Then ITQ-2 zeolite was obtained by using n-cetyltrimethylammonium bromide (CTAB) and tetrapro- pylammonium hydroxide (TPAOH) as...Using silica gel as the precursor, MCM-22(p) was synthesized under the static conditions. Then ITQ-2 zeolite was obtained by using n-cetyltrimethylammonium bromide (CTAB) and tetrapro- pylammonium hydroxide (TPAOH) as the swelling agents to swell the pores of MCM-22(p). The ob- tained zeolite was characterized by XRD, SEM, BET, NH3-TPD. The results show that the zeolite had the best swelling when MCM-22(p):CTAB:TPAOH=1:4:1. The synthesis duration and temperature did not influence significantly the pore swelling. Except TPAOH, CTAB can also be used together with tetrabuthylammonium hydroxide (TBAOH) as the pore swelling agent. There was contribution of sur- face area and pore volume from the mesoporous pores in the ITQ-2 zeolite and it also showed weaker acidity than MCM-22. However, the ITQ-2 supported NiW catalyst showed higher activity and selec- tivity to the middle distillates in the hydrocracking of vacuum gasoil (VGO) than MCM-22 supported catalyst. This implied that the diffusion of large molecules of heavy oil in the catalyst was facilitated due to the presence of the mesoporous pores and hence higher activity and selectivity to middle dis- tillates.展开更多
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.
文摘Using silica gel as the precursor, MCM-22(p) was synthesized under the static conditions. Then ITQ-2 zeolite was obtained by using n-cetyltrimethylammonium bromide (CTAB) and tetrapro- pylammonium hydroxide (TPAOH) as the swelling agents to swell the pores of MCM-22(p). The ob- tained zeolite was characterized by XRD, SEM, BET, NH3-TPD. The results show that the zeolite had the best swelling when MCM-22(p):CTAB:TPAOH=1:4:1. The synthesis duration and temperature did not influence significantly the pore swelling. Except TPAOH, CTAB can also be used together with tetrabuthylammonium hydroxide (TBAOH) as the pore swelling agent. There was contribution of sur- face area and pore volume from the mesoporous pores in the ITQ-2 zeolite and it also showed weaker acidity than MCM-22. However, the ITQ-2 supported NiW catalyst showed higher activity and selec- tivity to the middle distillates in the hydrocracking of vacuum gasoil (VGO) than MCM-22 supported catalyst. This implied that the diffusion of large molecules of heavy oil in the catalyst was facilitated due to the presence of the mesoporous pores and hence higher activity and selectivity to middle dis- tillates.
