Coupling conversion of CO/CO2 to chemicals through zeolite catalysis

Abstract

The coupling conversion of CO/CO₂ (COx), sourced from coal, natural gas, biomass, and other carbon sources, with substrates of alcohols, ethers, olefins and alkanes to produce valuable chemicals represents an attractive catalytic route for the direct utilization of COx carbon atoms. The majority of traditional COx conversion processes rely on hydrogenation or carbonylation reactions with metal catalysis. To date, zeolites containing protons in specific atomic scale channels or cages have emerged as one of the most important non-metallic heterogenous catalysts for the direct coupling of COx with a range of substrates (e.g., alcohols, ethers, olefins and alkanes), yielding products such as acids, esters, ketenes, and aromatics. Different from metal-based catalysis, zeolite-catalyzed COx coupling reactions generally proceed with alkyl cations and acyl cations as key intermediates, the stabilization of which is significantly enhanced within the intrinsic confined zeolitic reaction spaces. Typical processes include dimethyl ether (DME) carbonylation to methyl acetate (MAc), dimethoxy methane (DMM) carbonylation to methyl methoxyacetate (MMAc), olefin carbonylation to branched acids, the reaction of alkanes with COx to aromatics, etc. These cases demonstrate the great potential of zeolite in promoting efficient COx coupling. However, despite recent advances in mechanistic studies on DME carbonylation, the fundamental chemistry underlying zeolite-catalyzed COx coupling across widely applied catalytic systems remains insufficiently recognized. In this Perspective, we summarize decades of research on COx coupling catalysis over zeolites, including reaction mechanism, catalytic cycles, reaction kinetics and the structure-performance relationships. We also propose future outlooks for achieving a systematic and in-depth understanding of zeolite-catalyzed COx coupling chemistry, optimizing current process and developing new COx coupling processes.