The influence of acid strength and pore size effect on propene elimination reaction over zeolites: A theoretical study

Abstract The methanol-to-olefins (MTO) reaction over zeolite catalysts is very important for both fundamental research and industrial application to produce light olefins. In this study, the influences of the BrOnsted acid strength and pore size effect on the propene elimination in “hydrocarbon pool” (HCP) process over a series of zeolites are systematically investigated by density functional theory (DFT) calculations. The direct mechanism and indirect spiro mechanism with water as the proton transfer reagent in the propene elimination are considered. In the direct mechanism, the reactivity can be enhanced by increasing the acid strength. While, in the indirect mechanism, a moderate acidity is better. The indirect mechanism has a lower activation barrier than the direct one and thus is much more preferable. Because of the pore size effect, the SSZ-13 zeolite with the largest pore has the highest catalytic activity in the indirect mechanism. Following is the ZSM-5 zeolite. While, due to the serious steric hindrance, the reaction is hard to occur in the ZSM-22 zeolite with the smallest pore size.