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

The processes of methane combustion on three Pd-based diatomic catalysts (Pd-2, 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 Pd-2, PdPt and PdNi are compared. The main reaction path for methane combustion on catalyst Pd-2 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 Pd-2 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 = 1.0639x10(4) s(-1)) > Pd-2 (k = 1.7281x10(2) s(-1)) > PdNi (k = 1.9235x10 s(-1)). Thus, PdPt catalyst exhibits better performance than the other two catalysts in the methane catalytic combustion.