First-principles microkinetic simulations revealing the driving effect of zeolite in bifunctional catalysts for the conversion of syngas to olefins

Abstract

Direct conversion of syngas to light olefins (STO) on bifunctional catalysts has garnered significant attention, yet a comprehensive understanding of the reaction pathway and reaction kinetics remains elusive. Herein, we theoretically addressed the kinetics of the direct STO reaction on typical ZnAl₂O₄/zeolite catalysts by establishing a complete reaction network, consisting of methanol synthesis and conversion, water gas shift (WGS) reaction, olefin hydrogenation, and other relevant steps. The WGS reaction occurs very readily on ZnAl₂O₄ surface whereas which is less active towards alkane formation via olefin hydrogenation, and the latter can be attributed to the characteristics of the H₂ heterolytic activation and the weak polarity of olefins. The driving effect of zeolite component towards CO conversion was demonstrated by microkinetic simulations, which is sensitive to reaction conditions like space velocity and reaction temperature. Under a fixed ratio of active sites between oxide and zeolite components, the concept of the “impossible trinity” of high CO conversion, high olefin selectivity, and high space velocity can thus be manifested. This work thus provides a comprehensive kinetic picture on the direct STO conversion, offering valuable insights for the design of each component of bifunctional catalysts and the optimization of reaction conditions.