Insight into the Methylation of Alkenes and Aromatics with Methanol over Zeolite Catalysts by Linear Scaling Relations
Yanyan Chen, Xunhua Zhao, Zhangfeng Qin, Sen Wang, Zhihong Wei, Junfen Li, Mei Dong, Jianguo Wang, Weibin Fan
Abstract
It is now known that the methanol to hydrocarbon (MTH) processes over zeolite catalysts comply with the hydrocarbon pool (HCP) mechanism where the methylation of alkenes and aromatics determines the distribution of HCP species and thereon the activity and product selectivity of the zeolite catalyst in MTH to a great extent. In this work, the methylation of alkenes and aromatics in multiple zeolite frameworks was investigated by using density functional theory calculation, to clarify the catalyst structure–activity relationship and predict the distribution of HCP species. Three linear scaling relations (LSRs) were established: first, the energy of transition states is related to the energy of initial states for the successive methylation steps by a new transition-state scaling (TSS) relation; second, a Brønsted–Evans–Polanyi (BEP) relation between the energy barrier and reaction energy is built for the stepwise methylation; and third, the energy barrier and reaction rate of propene methylation are related to pyridine adsorption energy, suggesting that the pyridine adsorption energy can be used as a descriptor for the reactivity of propene in the stepwise methylation. These relations may provide an efficient way to predict the kinetic parameters from a limited number of well-defined energy terms and are helpful in clarifying the structure–activity relationship of the zeolite catalyst in MTH.