Theoretical research on a coke-resistant catalyst for the partial oxidation of methane: Pt/Cu single-atom alloys

Abstract

Cu can prevent carbon deposition on a surface due to weak adsorption, but it exhibits a high energy barrier to C–H bond activation, which means that it is not practical. Here, inspired by the catalytic properties of Pt and the strategy of single-atom alloys, a Pt₁Cu single-atom alloy (SAA) catalyst is built and studied. The primary goal is to understand the alloy's catalytic activity and coke-resistant properties during the partial oxidation of methane (POM) using density functional theory (DFT). Based on the wide application of Ni-based catalysts in POM, a parallel sample using a Pt₁Ni SAA catalyst is also studied. C–H bond activation and coke resistance are quantified by the activation energy barrier of CH₄ dissociation and the energy barrier of C₂ formation, respectively. It is shown that the Pt₁Cu SAA catalyst can promote activation of the C–H bond of CH₄, without affecting the excellent coke resistance. The first C–H cleavage is promoted by the introduction of a Pt single atom, and the activation energy barrier is 1.73 eV on the Cu(111) surface, while it is 1.16 eV on the Pt₁Cu(111) surface. The activation energy barrier of C₂ formation is 2.08 eV on the Cu(111) surface and 1.89 eV on the Pt₁Cu(111) surface. The properties of the Pt single-alloy Cu catalyst are obviously enhanced compared with reactions on commercial Ni-based catalysts. The activation energy barrier is 1.10 eV for CH₄ dissociation and 1.35 eV for C₂ formation with the Pt₁Ni SAA catalyst. Coke resistance is further elucidated by the method of changes of partial density of states (PDOS) and Mulliken charges in this work. The results on the electronic properties are consistent with the thermodynamic results. A reference strategy is provided in this work to promote the activation of the C–H bond and the coke-resistant performance during POM.