Dissociative adsorption of methane on surface oxide structures of Pd-Pt alloys

TL;DR

This study uses density-functional theory to analyze how methane dissociates on oxidized Pd, Pt, and Pd-Pt alloy surfaces, revealing how different oxide structures influence adsorption energies and potential methane-to-methanol conversion.

Contribution

It provides detailed insights into methane adsorption on various oxidized Pd-Pt alloy surfaces, highlighting the impact of oxide structure and composition on adsorption energetics.

Findings

Adsorption is endothermic on bare Pd(111) and stable oxide structures.

Large adsorption energies occur on PdO(100) and certain metastable oxide layers.

Thermodynamic preference for direct methane to methanol conversion on oxidized Pd-Pt surfaces.

Abstract

The dissociative adsorption of methane on variously oxidized Pd, Pt and Pd-Pt surfaces is investigated using density-functional theory, as a step towards understanding the combustion of methane on these materials. For Pd-Pt alloys, models of surface oxide structures are built on the basis of known oxides on Pd and Pt. The methane adsorption energy presents large variations depending on the oxide structure and composition. Adsorption is endothermic on the bare Pd(111) metal surface as well as on stable thin layer oxide structures such as the ($\sqrt{5}\times\sqrt{5}$) surface oxide on Pd(100) and the PtO$_2$-like oxide on Pt(111). Instead, large adsorption energies are obtained for the (100) surface of bulk PdO, for metastable mixed Pd$_{1-x}$Pt$_x$O$_{4/3}$ oxide layers on Pt(100), and for Pd-Pt(111) surfaces covered with one oxygen monolayer. In the latter case, we find a net thermodynamic preference for a direct conversion of methane to methanol, which remains adsorbed on the oxidized metal substrates via weak hydrogen-bond interactions.