Role of Oxygen during Methane Oxidation on Pd1/PdO1@CeO2 Surface: A Combined Density Functional Theory, Microkinetic, and Machine Learning Approach
Abstract
This work explores the role of oxygen in industrial methane oxidation. Oxygen, a well-known oxidizing agent, drives CH4 conversion to CO2 and H2O. We report how oxygen influences oxidation on single Pd and PdO clusters supported on CeO2(111). Oxygen is introduced by (1) lattice O in PdO and (2) O2 adsorption on an isolated Pd atom, forming PdOx clusters. Density-functional theory (DFT) mapped multiple reaction pathways on the Pd1/PdO1@CeO2(111) surface; both Pd and PdO clusters were found to thermodynamically favour methane activation. The computed barrier for CH4 activation is 0.63 eV on PdO1@CeO2(111). A single Pd atom markedly accelerates O2 dissociation to PdO2, and the presence of lattice oxygen lowers this barrier by 0.36 eV relative to an oxygen-deficient surface, enhancing catalytic efficiency. Reaction selectivity, coverage-dependent production rates, degree of rate control (DRC), and intrinsic turnover frequency (TOF) were quantified through steady-state microkinetic modelling. The simulations predict full conversion of CH4 to CO2 and H2O above 600 K, whereas partial-oxidation intermediates dominate at lower temperature and high O coverage. Rate constants for all elementary steps were derived via the Sure Independence Screening and Sparsifying Operator (SISSO) symbolic-regression method, yielding a concise predictive expression based on charge, coordination number, and key Pd-O/C-H distances. These combined DFT-microkinetic-SISSO results clarify oxygen's mechanistic participation and provide practical guidelines for designing Pd/CeO2 catalysts with improved activity toward methane oxidation, a reaction of pressing environmental and industrial importance.
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