DFT study of methane catalytic combustion on Pd-based diatomic catalysts

Abstract

The processes of methane combustion on three Pd-based diatomic catalysts (Pd2, PdPt and PdNi) are investigated by using density functional theory (DFT) at the B3LYP/6-311++G(d,p)+SDD//B3LYP/6-311G(d,p)+LANL2DZ level. The optimized geometric structures, activation energy (Ea ), and reaction rate constant (k) of methane dehydrogenation and oxidation on Pd2, PdPt and PdNi are compared. The main reaction path for methane combustion on catalyst Pd2 is CH4→CH3→CH2→CHOH→CHO→CO→CO2. However, the main reaction paths on catalyst PdPt and PdNi are the same: CH4→CH3→CH2OH→CHOH→CHO→CO→CO2. The rate-determining steps (RDS) on catalyst Pd2 and PdPt are the same: CHOH→CHO, while the step of CH3→CH2OH is the RDS on PdNi. Further analysis shows that the catalytic activity followed the order of PdPt (k = 1.0639×104 s-1) > Pd2 (k = 1.7281×102 s-1) > PdNi (k = 1.9235×10 s-1). Thus, PdPt catalyst exhibits better performance than the other two catalysts in the methane catalytic combustion.