Promotional Effect of Dispersant Modification to ZnCr on CO<sub>2</sub> Hydrogenation into Aromatics over Hybrid Catalysts
Junfeng Zhang, Kaiwen Zheng, Xiaoxing Wang, Qingde Zhang, Chunyang Zeng, Yisheng Tan
Abstract
The hybrid catalyst through coupling metal oxides and zeolite is a strategy for converting CO2 to the targeted hydrocarbons containing aromatics. Herein, we framed an active hybrid catalyst comprising ZnCr oxide and HZSM-5 zeolite for conversion of CO2 to aromatics. The usage of dispersants (PEG or TPABr) in the process of preparing ZnCr oxide is certainly effective to improve the yield of aromatics. Over the hybrid catalyst ZnCr-TPABr + HZSM-5 with TPABr as a dispersant, the total hydrocarbon (HCt) selectivity increases to 37.4% at 330 °C, obviously higher than that over the hybrid catalyst ZnCr-none + HZSM-5 without a dispersant (29.5%), wherein C5+ hydrocarbons in the HCt account for above 69%. Moreover, the proportion of aromatics in C5+ products is improved to 87.9 from 79.4%. Multitechnique characterizations demonstrate that the usage of the TPABr dispersant induces smaller crystal sizes, the formation of more nonstoichiometric ZnCrxOy spinels and oxygen vacancies, and the accumulation of ZnO on the surface of the ZnCr-TPABr oxide, which are in favor of the adsorption of CO2 and the formation of the intermediate methanol or its precursor, methoxyl, finally leading to the improved catalytic performance.