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

Mesoporous MgAl(2)O(4 )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(degrees)). 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(degrees)) and wet conditions (380 (degrees)), 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(degrees)) and the highest redox capability. Additionally, O2 temperature-programmed oxidation further elucidates that PdOx 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/MgAl(2)O4-y catalysts. A comparable trend is also evident in the correlation between Pd particle size and TOF.