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 (E_a ), 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.