The new role of surface adsorbed CHx(x = 1–3) intermediates as a co-adsorbed promoter in self-promoting syngas conversion to form CHx intermediates and C2 oxygenates on the Rh-doped Cu catalyst

Abstract

Syngas conversion to C2 oxygenates includes two crucial steps that CO activation to form CHx(x = 1–3) intermediates, followed by its reaction with CO/CHO to form the CC chain, in which the CHx(x = 1–3) intermediates were widely recognized as the reactive intermediates to yield C2 oxygenates. Inspired by the reported studies about the role of co-adsorbed OH intermediates that promote CO activation and the CC chain formation in syngas conversion, an idea about the new role of surface adsorbed CHx intermediates in syngas conversion is proposed, that is, whether the surface adsorbed CHx intermediates itself also act as a co-adsorbed promoter to self-promote CO activation and conversion. This study revealed for the first time that in syngas conversion to C2 oxygenates over Rh-doped Cu catalysts, the surface adsorbed CHx(x = 1–3) intermediates not only act as the reactive intermediates to participate into the reactions with CO/CHO, but also itself act as a self-promoter to facilitate CO activation to form CHx(x = 1–3) intermediates and promote CHO reaction with CHx(x = 1–3) to form C2 oxygenates. Especially, the dominant CH2 intermediate acted as a co-adsorbed promoter exhibits higher activity and selectivity towards itself formation and C2 oxygenates CH2CHO instead of methanol and hydrocarbons, respectively. Moreover, the internal mechanism of surface adsorbed CHx intermediate is explained from the electronic property aspect. This newly so-called CHx self-promoting syngas conversion mechanism offers new insights into the fundamental role of surface adsorbed CHx(x = 1–3) intermediates in CO activation and conversion to form C2 oxygenates, and open a new mechanism that is likely general and involved in the reactions related to CHx(x = 1–3) intermediates formation.