Highly Active and Stable Pd/MgAl2O4 Catalysts for Methane Catalytic Combustion

Mesoporous MgAl₂O₄ is synthesized via a novel sol–gel combustion method and the concentration of oxygen defects on the surface is modulated through varying the calcination temperature (850, 900, 1000, and 1100 °C). Notably, the 1Pd/MgAl₂O₄-1000 catalyst exhibits superior catalytic activity and stability. The turnover frequency (TOF) for 1Pd/MgAl₂O₄-1000 is 0.079 and 0.058 s⁻¹ under dry conditions (300 °C) and wet conditions (380 °C), respectively. The results of H₂ temperature-programmed reduction and X-Ray photoelectron spectroscopy reveal that the principal active species within the Pd/MgAl₂O₄-y catalyst is PdO. Specifically, the Pd–MgAl₂O₄-1000 catalyst exhibits the lowest temperature reduction peak (120 °C) and the highest redox capability. Additionally, O₂ temperature-programmed oxidation further elucidates that PdO_x species in the Pd/MgAl₂O₄-1000 catalyst is prone to decomposition and the resultant palladium metal is readily reoxidized. Consequently, the rapidity of the redox cycle between PdO and Pd⁰ emerges as a pivotal factor in CH₄ catalytic combustion. Furthermore, a correlation analysis among catalyst particle size, oxygen defect concentration, and TOF is conducted. The findings illustrate a distinct volcano-shaped curve in the relationship between oxygen defect concentration and TOF for the 1Pd/MgAl₂O₄−y catalysts. A comparable trend is also evident in the correlation between Pd particle size and TOF.