The kinetic basis of bifunctional OX–ZEO catalysts for syngas conversion to light olefins

Abstract

Despite considerable progress in oxide–zeolite (OX–ZEO) bifunctional catalysts for ketene-mediated syngas conversion, the origin of inter-component synergy and its dependence on spatial proximity remain unclear. Here we develop a diffusion-bridged, two-component microkinetic model that incorporates the entire reaction network over the ZnCrOx/mordenite (MOR) catalyst. The model captures the coupled reaction–diffusion dynamics and quantitatively elucidates the synergetic mechanism underlying selective syngas-to-light-olefin conversion. We show that MOR enhances light-olefin selectivity by overcoming the thermodynamic limitation of CH2CO formation on the oxide via a more favourable pathway. Furthermore, the model predicts an inverted U-shaped dependence of light-olefin selectivity with proximity, arising from a balance between intermediate transfer and Zn migration, the latter generating [ZnOH]+ species that promote undesired hydrogenation. More broadly, we establish a general reaction–diffusion coupling kinetic framework that quantifies the optimal combination principles for OX–ZEO systems. The predictions agree well with experimental observations and provide guidance for designing high-performance bifunctional catalysts. Bifunctional oxide–zeolite catalysts work in tandem to produce light olefins from syngas, but the precise mechanistic picture is complex and remains elusive. Now the reaction mechanism on a ZnCrOx/mordenite catalyst is studied in detail using a diffusion-bridged microkinetic model, and design principles are proposed.