Balanced Diffusion and Acidity for Enhanced CO2 Hydrogenation to Light Aromatics over ZnZrO x /ZSM-5 Catalysts

Abstract Low-temperature hydrogenation of CO2 into aromatics has received significant attention. However, without employing post-treatment synthesis to passivate the external surface acidity of zeolites, it remains a big challenge to achieve higher efficiency in the synthesis of high-value aromatics with carbon chain numbers less than 10. Herein, we designed a ZnZrOx/ZSM-5 catalyst and achieved a CO2 conversion of 13.3% and a total aromatic selectivity of 77.5% (CO-free), including 21.0% BTX (benzene, toluene, and xylene) and 56.7% C9 aromatics at a low temperature of 310 °C. By introducing mesoporous carbon into the precursors, the resultant ZSM-5 zeolites exhibit a coffin morphology with tunable b-axis thickness and reduced surface acidity. When tetraethyl orthosilicate is further employed as the silica source, a higher concentration of framework Al (AlF) species is preferentially positioned at the channel intersections of ZSM-5, thereby enhancing the aromatic cycle and the diffusion of aromatic products out of the channels. We demonstrate that the balance of diffusion and acidity (including acid density, strength, and distribution) of zeolites enables efficient synthesis of aromatics with selective chain number (C6−C9) from CO2 hydrogenation over this bifunctional catalyst. Moreover, in situ DRIFTS spectra confirm that oxygen-containing species are key intermediates in the methanol synthesis pathway, which subsequently undergo C−C coupling reactions to yield aromatics. This work offers innovative design principles for zeolite microenvironment engineering and high-performance bifunctional catalysts for light aromatic synthesis without degradation of the catalytic performance.