Tuning the A-site cation in spinel MAl2O4 (M = Co, Mg, Zn, Cu) supports enables superior Pd-Catalyzed hydrodechlorination of 4-Chlorophenol

Chlorinated phenols are priority pollutants that require efficient low-temperature removal technologies. Here, we synthesize a series of spinel-type MAl 2 O 4 (M = Co, Mg, Zn, Cu) supports and deposit 1 wt% Pd via incipient-wetness impregnation to evaluate their hydrodechlorination (HDC) performance toward 4-chlorophenol under ambient aqueous conditions (30 °C, 0.2 MPa H 2 ). Catalytic screening shows that the identity of the divalent A-site cation strongly modulates activity: Pd/Co-Al achieves 91.8 % conversion with > 98.3 % selectivity to phenol, outperforming Pd/Ni-Al (84.7 %) and the remaining analogues. Pd/Cu-Al exhibits almost no conversion (<5.0 %), while Pd/Mg-Al and Pd/Zn-Al give moderate conversions (ca.55.4–58.7 %). Detailed characterization by XRD, N 2 -physisorption, H 2 -TPR, XPS and STEM reveals that the superior performance of Pd/Co-Al is rooted in (i) strong metal–support interactions that stabilize a balanced Pd 2+ /Pd 0 surface ensemble, (ii) coherent lattice matching at Pd(1   1   1)/CoAl 2 O 4 (311) interfaces that suppress particle growth, and (iii) high spinel thermostability that mitigates leaching and coking. A 30 h continuous-flow test confirms stable operation without activity loss. This work elucidates how subtle variations in spinel composition dictate Pd electronic structure and interfacial geometry, providing design principles for next-generation HDC catalysts.