Identification of the active site during CF4 hydrolytic decomposition over γ-Al2O3

Abstract

Aluminum production processes emit carbon tetrafluoride (CF₄) directly into the atmosphere, which is a powerful greenhouse gas (with a greenhouse warming potential 6500 times that of CO₂) with serious potential to exacerbate global warming. As the most feasible method of eliminating CF₄, the hydrolytic decomposition of CF₄ at moderate temperatures is still challenging due to the active site remaining elusive. Herein, we demonstrated that three-coordinated Al (Al_III) on the γ-Al₂O₃ (110) surface is the dominant active site during the hydrolytic decomposition of CF₄. DFT calculations present the strong adsorption of CF₄ on the Al_III site. γ-Al₂O₃ nano-slices with exposed (110) crystal planes with different Al_III occupation levels were synthesized. The amounts of Al_III in the catalysts were quantified via²⁷Al MAS NMR and the number of Al_III sites directly affects the catalytic activity. In situ FTIR spectra show that the Al_III sites could be activated and that they had a stable presence under the given reaction conditions.