Unveiling Tetrafluoromethane Decomposition over Alumina Catalysts
Tao Luo, Hang Zhang, Yingkang Chen, Shanyong Chen, Yang Pan, Kang Liu, Junwei Fu, Liyuan Chai, Zhang Lin, Michelle L. Coote, Min Liu
Abstract
Tetrafluoromethane (CF 4 ), the simplest perfluorocompound known as a “forever chemical”, presents substantial environmental challenges due to its health risks and contribution to the greenhouse effect. Designing efficient catalysts for CF 4 decomposition remains difficult, compounded by limited understanding of the mechanisms. Here, we use constrained ab initio molecular dynamics (cAIMD) simulations and in situ experiments to elucidate the mechanism of alumina-catalyzed CF 4 decomposition, highlighting the pivotal role of surface hydroxyl groups. The initial C–F bond breaking is the rate-determining step, with surface hydroxyl groups reducing the reaction free energy from 1.69 to 1.34 eV. These hydroxyl groups also facilitate the self-healing of oxygen vacancies generated during the decomposition. Contrary to the belief that CF 4 decomposes directly into CO 2, our cAIMD simulations, supported by synchrotron vacuum ultraviolet photoionization mass spectrometry data, reveal significant CF 2 O and CO byproducts. Experimental data in an anhydrous environment indicate that water primarily replenishes surface hydroxyl groups rather than directly participating in decomposition. We conclude that the relatively high efficiency of Al 2 O 3 catalysts stems from three key properties: (1) the presence of active sites with a specific affinity for CF 4 adsorption, ensuring efficient substrate interaction; (2) appropriate metal–oxygen bond strength, enabling the participation of lattice oxygen in the reaction; and (3) a high density of surface hydroxyl groups that facilitate the initial C–F bond cleavage and the self-healing of oxygen vacancies.