Hydrogen transfer reaction contributes to the dynamic evolution of zeolite-catalyzed methanol and dimethyl ether conversions: Insight into formaldehyde

Abstract

Formaldehyde (HCHO), generating from hydrogen transfer (HT) of reactant, is significant for autocatalysis initiation and deactivation in methanol-to-olefins (MTO), but hitherto, its evolution throughout the reaction has not been thoroughly revealed. Herein, by the established colorimetric analysis method, HCHO in the MTO and dimethyl ether (DME)-to-olefins (DTO) reactions over SAPO-34 was in situ quantitatively monitored, where HCHO was detected in slight and conspicuous amounts at initial and deactivation stages with semi-conversion, also when co-fed with water or high-pressure H2. We reveal the weak HT ability of DME relative to methanol, which enables prominent olefins-based cycle and suppresses reactant-induced HT and deactivation in DTO (which is critical for MTO). A complete dynamic reaction network is disclosed, constituting two simultaneous and interplaying pathways: the main reactions for olefin generation as the open-line and HT reactions as the hidden-line. Especially, co-feeding high-pressure H2 with DME capacitating a long-term and highly efficient operation of DTO by modulating the dynamic reaction network to a more moderate autocatalysis evolution, has great potential in industry application.