Optimizing Gallium Hydrides for Enhanced CO<sub>2</sub> Hydrogenation to Aromatics with GaZrO<sub><i>x</i></sub>-ZSM-5 Tandem Catalysts
Siyuan Huang, Xia Wang, Chengsheng Yang, Jia Liu, Bilyu Hong, Shuyi Li, Yifeng Zhu, Youzhu Yuan
Abstract
The direct conversion of CO 2 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 CO 2 conversion due to challenges in CO 2 activation, particularly in understanding the role of metal hydride species. In this study, we synthesized stable GaZrO x 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 GaZrO x 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 CO 2 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 CO 2 to aromatics.