Effect of Al Location and Ga Species in ZSM-5 on Adsorption of Soluble Coke.

During the methanol-to-hydrocarbons process catalyzed by H-ZSM-5, coke deposition occurs and can severely hinder the reaction. The effect of Al location and Ga species in ZSM-5 on the adsorption of soluble coke was investigated using density functional theory calculations with the ONIOM method. The results show that soluble coke is adsorbed more stably when Al is situated at straight channels and channel intersections than that in the sinusoidal channel. For Ga species, Ga(OH)2+, GaO+ and GaH2+ are found to readily adsorb soluble coke compared with GaH2 +, GaH(OH)+, and Ga+. Further analysis reveals that the acid strength of Ga species does not exhibit a linear correlation with the adsorption energy of soluble coke. Apart from pyrene that fails to be stably adsorbed, the charge variation of Ga species shows an inverted-volcano-shaped correlation with the adsorption energies of aromatics. Our work provides theoretical references and data support for the design of anti-coking zeolite catalysts and the precise regulation of active sites.