Regulating silanols in MFI zeolites toward rational design of anti-coking catalysts for methane dehydroaromatization

Abstract

The rapid deactivation of zeolite catalysts via coking remains a critical challenge in methane dehydroaromatization (MDA). While the roles of Mo sites and Brønsted acid sites (BASs) are well-documented, the contribution of silanol defects remains critically overlooked. Herein, we combine theoretical and experimental approaches to establish that silanol defects are pivotal in accelerating coke deposition. Theoretical calculations identify their strong adsorption affinity (2.87–4.53 eV) toward coke precursors like C₆H₆ and C₈H₁₀. By precisely engineering the concentration and spatial distribution of silanols in MFI zeolites, we demonstrate experimentally that external silanols drive coke accumulation and graphitization more aggressively than internal silanol nests. Building on this insight, we developed an ethylenediamine assisted surface modification strategy that selectively passivates external silanols and BASs while optimizing the intra-channel BAS density. This rational design enhances aromatics yield by 32.2%, reduces total coke deposition by 18.6%, and effectively reduces external coking. This work, for the first time, elucidates the critical and spatially dependent role of silanol defects in MDA coking and provides a targeted surface engineering route to design zeolite catalysts with superior anti-coking stability.