Selective Conversion of CO<sub>2</sub> to Trimethylbenzene and Ethene by Hydrogenation over a Bifunctional ZnCrO<sub><i>x</i></sub>/H-ZSM-5 Composite Catalyst
Shujia Guo, Sheng Fan, Han Wang, Sen Wang, Zhangfeng Qin, Mei Dong, Weibin Fan, Jianguo Wang
Abstract
Selective conversion of CO 2 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 CO 2 into trimethylbenzene (TriMB) and ethene by hydrogenation. The selectivities to aromatics and light olefins reach 64.6 and 26.1%, respectively, at a CO 2 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 CO 2 conversion keeps to the tandem methanol-mediated reaction route, viz., CO 2 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 C 9 -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 CO 2 hydrogenation. The insight shown in this work may give valuable clues for the design of efficient catalysts in the conversion of CO 2 to a specific hydrocarbon product.