Nickel Aluminum Spinel Derived Ni-F-Al Active Site for the Catalytic Dehydrofluorination of Potent Greenhouse Gas 1,1,1,2-Tetrafluoroethane

Abstract

HFC-134a (1,1,1,2-tetrafluoroethane) is one of the most common refrigerants with global warming potential (100 years) of 1300. It is regulated to be phased out gradually according to the Kigali Amendment to the Montreal Protocol. Treatment of this stable chemical poses significant challenge. Highly efficient nickel aluminum spinel catalysts were fabricated by sol–gel method for the catalytic dehydrofluorination of HFC-134a. The effect of Ni/Al ratio in the NiAl₂O₄ spinel precursors on the performance of NiAl catalysts was studied by x-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), transmission electron microscopy (TEM), NH₃-TPD, and XPS. Nickel–aluminum ratio in the nickel–aluminum spinel precursor plays a major role on the formation of strong acid and active species Ni-F-Al. With Ni/Al ratio of 4, the (3 1 1) crystal face of NiAl₂O₄ interfaced with the (1 1 1) crystal face of NiO and the (4 0 0) crystal face of NiAl₂O₄. This interaction facilitates the formation of Ni-F-Al active species following the dehydrofluorination reaction. Furthermore, the Ni-F-Al species altered the acid structure of NiAl catalysts. It was found that NiAl catalyst with a Ni/Al ratio of 4 has the best catalytic performance compared with other catalysts (with conversion of 35%), and no deactivation trend was observed after 50 h of time on stream. (Reaction conditions: N₂/CF₃CH₂F = 10, T = 450°C, GHSV = 660 h⁻¹).