Seed-fused ZSM-5 nanosheet as a superior MTP catalyst: Synergy of micro/mesopore and inter/external acidity

摘要

ZSM-5 nanosheet (NS) has an optimal diffusivity due to b-axis oriented two-dimensional structure, but the extra large external acidity results in the deactivation of the catalyst in methanol to propylene (MTP) reaction. The seed-fused ZSM-5 nanosheets (CNS-x) were synthesized by a seed induced method, the performance of samples was compared with one without seed. Further, the B-incorporation sample (B-CNS-5) was prepared with 5 wt% seed and boron acid. Revealing the importance of fusion effect of ZSM-5 seed on the nanosheet, especially the change in microstructure properties and its structure-effect relationship, which is not explicitly documented in previous work. With the seed amount increasing from 5 to 30 wt % in the gel, the crystallization time is largely shortened, along with the change in the resulting nanosheet, such as reduction of particle size and acid strength/ external surface acidity, an increase of over 50% micropore volume. The CNS-x samples perform longer catalytic lifetime (168-226 h) compared to NS (103 h). CNS-5 displays an extremely high selectivity to propylene (C = 3) similar to 54% and total light olefins (C = 2-C = 4) of similar to 84%. A super sample B-CNS-5 exhibits longest lifetime (302 h), achieving highest C = 3 yield due to change in the acid sites distribution and increase of extra weak acid sites. For the converted methanol (g/g(catal)(yst)), the result is B-CNS-5 (966) CNS-5 (525) NS (324). In converse, the average coke selectivity (S-av,S- c) is B-CNS-5 (0.18 parts per thousand) the CNS-5 (0.299 parts per thousand) NS (0.47 parts per thousand). This result offers new insight for MTP catalyst about the synergy of acidity and diffusion in the ZSM-5 nanosheet.