Optimizing Gallium Hydrides for Enhanced CO2 Hydrogenation to Aromatics with GaZrOx-ZSM-5 Tandem Catalysts

The direct conversion of CO2 to aromatics using tandem catalysts presents an efficient approach to mitigating carbon emissions. Although composite oxide-zeolite tandem systems via methanol intermediates exhibit high selectivity toward aromatics, they feature moderate levels of CO2 conversion due to challenges in CO2 activation, particularly in understanding the role of metal hydride species. In this study, we synthesized stable GaZrOx composite oxides and identified the critical function of Ga–H species under hydrogen-rich conditions. Our findings demonstrate that high coverage of Ga–H species on the GaZrOx surface facilitates the formation of HCOO* intermediates, thereby enhancing selectivity toward aromatics when integrated with the ZSM-5 zeolite. Unlike the previous reports, our data reveal that the homolytic dissociation of hydrogen, triggered by an initial heterolytic process, serves as the dominant mechanism, boosting the space-time yield of aromatics by 2.3 times and achieving a CO2 conversion of 14.3% and 82.8% selectivity for aromatics under optimized conditions. However, a high Ga/Zr molar ratio leads to the formation of the Ga–Ga bond, which reduces the selectivity of aromatics. These insights into the behavior of Ga–H species through homolytic dissociation offer a potential framework for designing efficient tandem systems composed of composite oxides and ZSM-5 in the hydrogenation of CO2 to aromatics.