Selective Conversion of CO₂ to Trimethylbenzene and Ethene by Hydrogenation over a Bifunctional ZnCrO_x/H-ZSM-5 Composite Catalyst

Abstract

Selective conversion of CO2 into a specific hydrocarbon is highly desirable but rather challenging. Herein, a bifunctional ZnCrO x /H-ZSM-5 composite catalyst was designed, which can selectively convert CO2 into trimethylbenzene (TriMB) and ethene by hydrogenation. The selectivities to aromatics and light olefins reach 64.6 and 26.1%, respectively, at a CO2 conversion of 17.5%. In particular, TriMB accounts for 57.4% of the aromatic products, while ethene takes up 83.9% of all light olefins. Various characterization and DFT calculation results reveal that the CO2 conversion keeps to the tandem methanol-mediated reaction route, viz., CO2 is first hydrogenated to methanol-related intermediates over the ZnCrO x moiety and the H-ZSM-5 moiety then carries on the further conversion of emerged intermediates to hydrocarbons via the hydrocarbon pool mechanism. The 10-ring channels of the ZSM-5 framework combined with an appropriate quantity and distribution of acid sites conduce to the formation of TriMB and meanwhile inhibit the C9-aromatics from further methylation; in addition, compared with propene and butene, ethene survives well from further evolution due to the higher energy barriers for ethene methylation and dimerization. All of these endue the ZnCrO x /H-ZSM-5 composite catalyst with a high selectivity to TriMB and ethene in the CO2 hydrogenation. The insight shown in this work may give valuable clues for the design of efficient catalysts in the conversion of CO2 to a specific hydrocarbon product.

Upgrading Trimethylbenzene to Durene by CO2-Mediated Methylation over Cu-Boosted ZnZrOx Integrated with HZSM-5

“…The advancement of carbon capture and utilization technologies, especially through catalytic processes, addresses environmental concerns while transforming waste into valuable commodities, providing economic benefits . Numerous studies have successfully transformed CO 2 into various value-added chemicals, such as formic acid, methanol, − light olefins, gasoline, and aromatics. − Among these, the hydrogenation of CO 2 to aromatics stands out as a particularly promising but challenging process, primarily due to the low selectivity for light aromatics (a few surpassed 40% for benzene, toluene, and xylene combined). , However, there are methods for CO x hydrogenation of aromatics to enhance the selectivity for producing heavier aromatics (C 9+ ), such as decreasing the feed gas space velocity, , modifying the pore structure of zeolites − and adjusting the distribution of acid sites . Preferably, introducing additional aromatics into the CO x hydrogenation process, catalyzed by metal oxide–zeolite composites, can enhance the production of specific aromatics significantly. − This method not only favors the generation of C 2+ -alkylated aromatics but also aligns with the objective of producing value-added aromatics in a carbon-neutral manner.…”

Boosting Benzene Alkylation Conversion with CO2/H2 via a Triple Composite Catalyst

“…Great efforts have been devoted to the conversion of CO 2 into BTX via the CO 2 -modified Fischer–Tropsch synthesis route − (CO 2 -FTS) and the methanol-intermediate route − over a bifunctional catalyst (Figure , routes A and B). The light olefins or methanol intermediate from CO 2 hydrogenation can be converted into aromatics in ZSM-5 channels via oligomerization, cyclization, dehydrogenation, and aromatization reactions. − These complex processes inevitably produce light hydrocarbons and aliphatics .…”