The deactivation mechanism of two typical shape-selective HZSM-5 catalysts for alkylation of toluene with methanol

Abstract

Two typical shape-selective HZSM-5 catalysts were prepared by silica deposition and La₂O₃ loading, respectively. They were characterized by means of XRD, BET, NH₃-TPD and Py-IR and were tested by alkylation of toluene with methanol. The deactivation mechanism of these catalysts in the alkylation was studied in detail by using TG, BET, NH₃-TPD, Py-IR, and soluble coke extraction/GC-MS. The results indicated that the invalidation of internal acid sites deactivated both catalysts which have different deactivation processes. Concretely, the fast deactivation of SiO₂-HZSM-5 is due to the microporous blockage caused by soluble coke, which is composed of multi-methylbenzenes, polyaromatics and large olefins. Whereas, the invalidation of the internal acid sites on La₂O₃-HZSM-5 results from the accumulation of multi-methylbenzenes, naphthalenes, and large aliphatic compounds inside ZSM-5 channels and the subsequent micropore blocking by insoluble coke.