Stabilizing Pd Catalysts on Pentacoordinated Al3+ Sites of Alumina for Efficient Hydrogenation of Hexafluoropropylene

Achieving high dispersion and stability of noble metals on conventional supports remains a key challenge in catalysis. Herein, we address this issue by designing an alumina support enriched with pentacoordinated Al 3+ (Al 3+ penta) sites, which serve as effective anchoring centers for Pd species. The catalyst was applied to the gas-phase hydrogenation of hexafluoropropylene (HFP), a critical step in the synthesis of the low-global-warming-potential refrigerant HFO-1234yf. Comprehensive characterization, including 27 Al MAS NMR, XPS, and HRTEM suggest that the Al 3+ penta sites strongly interact with Pd, forming Pd-O-Al bridge structures, thereby suppressing Pd aggregation and enhancing Pd dispersion. The optimized 0.5 wt% Pd/EA-Al 2 O 3 catalyst achieved approximately 92% HFP conversion at 90°C, significantly outperforming conventional Pd/γ-Al 2 O 3 counterpart. This work underscores the decisive role of Al 3+ penta sites in regulating metal-support interactions and provides a viable strategy for designing efficient catalysts with reduced noble-metal loadings. Graphical The abundant penta-coordinated Al 3+ sites in EA-Al 2 O 3 strongly anchor PdO through the formation of stable Pd-O-Al linkages, enabling PdO to remain oxidized and highly dispersed even after H 2 reduction. In contrast, PdO on commercial γ-Al 2 O 3 is fully reduced to metallic Pd and undergoes significant agglomeration. This anchoring effect markedly enhances the catalytic activity and stability in the hydrogenation of HFP to HFC-236ea.