Regulating the Aromatics Distribution over Bifunctional Catalyst by Hydrogen Spillover in CO2 Hydrogenation

Direct conversion of CO2 to aromatics has received considerable attention as a typical CO2 utilization technology for mitigating climate change. Efficiently regulating the distribution of aromatics remains a significant challenge. Here, we report on a series of bifunctional catalysts composed of Na/Fe and Ni/ZSM-5 zeolites with varying Ni content, which achieve a controlled distribution of aromatics in direct CO2 hydrogenation to aromatics. The hydrogen spillover effect of Ni on ZSM-5 accelerates the cracking of aromatics and consequently increases the BTX (benzene, toluene, xylene) content in the aromatics to as much as 78.4% (mol %). Ethylbenzene dealkylation as a model reaction reveals that introduction of Ni facilitates the removal of branched chains from aromatics in the form of CH4, leading to a positive correlation between CH4 selectivity and the BTX ratio in aromatics with the amount of spillover hydrogen. The hydrogen spillover effect also significantly reduced the coke content on HZSM-5, prolonging the catalyst life. However, excessive hydrogen spillover increases the hydrogen coverage on Fe species, inhibiting the carburization of Fe, which is unfavorable for CO2 conversion. These insights offer a new strategy for controlling the distribution of aromatics over bifunctional catalysts over the conversion of C1 to aromatics.