Factors influencing the stability of ZSM-5-based catalyst

A series of ZSM-5-based catalysts with different reaction durations, i.e. fresh, used for 48h, used for 650h, used for 650h and then regenerated, as well as the regenerated one reused for another 48h, were characterized to investigate the factors that influence the stability of ZSM-5-based catalyst for the conversion of C₄ olefin to propylene. The results indicted that both of the micropore volume and the BJH adsorption cumulative volume of pores are dropped after long term reaction; after regeneration, they are nearly recovered to the original values of the fresh catalyst. Meanwhile, the acid amount determined by NH₃-TPD is also decreased, but it cannot be recovered after regeneration. Comparing with the results of the catalyst pretreated by steam at the same temperature, the ²7Al MAS NMR results suggested that the effect of coke deposition on the pore volume can be completely eliminated through regeneration, however, the dealuminum of zeolite and the decrease of cell parameters may lead to the permanent loss of the catalyst activity. After a long duration under high temperature and water steam, the acid amount of the ZSM-5-based catalyst can be maintained at a relatively stable level, which then makes a long term stable reaction operation possible.