Methane oxidation on Pd–Ceria: A DFT study of the mechanism over PdₓCe- ₓO₂, Pd, and PdO
2011
Mayernick, Adam D. | Janik, Michael J.
Palladium/ceria exhibits unique catalytic activity for hydrocarbon oxidation; however, the chemical and structural properties of active sites on the palladium–ceria surface are difficult to characterize. Strong interactions between palladium and the ceria support stabilize oxidized Pdᵟ ⁺ species, which may contribute to the significant activity of Pd/ceria for methane oxidation. We present a density functional theory (DFT+U) investigation into methane oxidation over Pd/ceria and quantify the activity of the PdₓCe₁₋ ₓO₂(111) mixed oxide surface in comparison with the PdO(100) and Pd(111) surfaces. The methane activation barrier is lowest over the PdₓCe₁₋ ₓO₂(111) surface, even lower than over the Pd(111) surface or low coordinated stepped or kinked Pd sites. Subsequent reaction steps in complete oxidation, including product desorption and vacancy refilling, are considered to substantiate that methane activation remains the rate-limiting step despite the low barrier over PdₓCe₁₋ ₓO₂(111). The low barrier over the PdₓCe₁₋ ₓO₂(111) surface demonstrates that mixed ceria-noble metal oxides offer the potential for improved hydrocarbon oxidation performance with respect to dispersed noble metal particles on ceria.
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