Tuning the Local Coordination and Electronic Metal–Support Interaction of Pd Single-Atom Catalysts for Methane Combustion

Abstract Tuning the local coordination environment and electronic metal–support interaction (EMSI) via support modulation is critical for optimizing the catalytic performance of Pd single-atom catalysts (SACs) in methane (CH4) combustion. Yet their synergistic regulation remains elusive. Herein, a series of Pd1/M SACs (M = NiO, SnO2, TiO2, and CeO2) with identical Pd loadings was facilely prepared using a one-step flame spray pyrolysis (FSP) method. The results reveal that support modulation tunes the local coordination environment and EMSI in Pd1/M SACs, thereby influencing their catalytic performance and stability in CH4 combustion. A coupled coordination–defect–electronic effect arises from strong EMSI and abundant oxygen vacancies (OV) in Pd1/NiO. This effect facilitates CH4 adsorption and activation, resulting in the lowest T50 (357 °C) and enhanced stability compared with Pd1/TiO2, which exhibits moderate EMSI. In contrast, CeO2 stabilizes an over-coordinated Pd–O4.3 local environment under weak EMSI, leading to a CH4 conversion of less than 10% at 450 °C. In-situ diffuse reflectance infrared Fourier transform spectroscopy, in-situ X-ray absorption spectroscopy combined with density functional theory (DFT) calculations reveal that CH4 combustion over Pd1/NiO follows the Mars–van Krevelen mechanism: Pd1–OV–Ni active sites serve as adsorption and activation centers for gaseous CH4, and lattice oxygen subsequently converts the adsorbed reactant into CO2 via formate and carbonate intermediates. By contrast, the over-coordinated Pd single atoms in Pd1/CeO2 exhibit poor CH4 adsorption and activation, resulting in the surface accumulation of abundant formate and carbonate intermediates that cannot be further converted into CO2. This work provides crucial insights into tuning the local coordination environment and EMSI via support modulation for simultaneously achieving high activity and stability in Pd SACs.