Coupling conversion of CO/CO₂ to chemicals through zeolite catalysis

The coupling conversion of CO/CO₂ (CO _x ), 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 CO _x carbon atoms. The majority of traditional CO _x 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 heterogeneous catalysts for the direct coupling of CO _x 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 CO _x 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 CO _x to aromatics, etc. These cases demonstrate the great potential of zeolite in promoting efficient CO _x coupling. However, despite recent advances in mechanistic studies on DME carbonylation, the fundamental chemistry underlying zeolite-catalyzed CO _x coupling across widely applied catalytic systems remains insufficiently understood. In this perspective, we summarize decades of research on CO _x coupling catalysis over zeolites, including reaction mechanisms, 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 CO _x coupling chemistry, optimizing current processes and developing new CO _x coupling processes.