Direct Conversion of Syngas to Light Olefins: Construction of Reaction Network and Design of Oxide-Zeolite Bifunctional Catalysts

Abstract: The direct synthesis of light olefins from syngas over a bifunctional catalyst containing oxide and zeolite has proven to be a promising strategy. Nevertheless, unclear reaction network hinder the further enhancement of catalytic performance, such as increasing CO conversion and olefin/praffin ratio. We herein synthesis a series of bifunctional catalysts containing oxides (InZr, ZnAl, ZnCr, MoS₂, etc.) and zeolites (SAPO or AlPO zeolites with CHA, AEI, ERI, AFN topologies). A complete reaction network is proposed via DFT calculations and model reactions, including CO activation, intermediate diffusion, C-C coupling, hydrogenation, etc. We demonstrate that methanol is the key intermediate to be transformed into light olefins in zeolites and inhibiting excessive hydrogenation is an effective strategy to achieve higher performance. In addtion, we also find that zeolite is the key component for determining olefin/paraffin ratio of hydrocarbon products. By optimizing the particle size, the density and strength of acid sites and the framework structure of zeolites, we design a novel bifunctional catalyst showing superior olefin/paraffin ratio and high stability at mild reaction conditions. According to the reaction network, we also propose an integration manner of the bifunctional catalysts which can be used in commercial production. These findings will greatly boost the industrialization of lower olefins synthesis from syngas.

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