关键词: 甲烷氧化, Pd基催化剂, 氧空位, 密度泛函理论, 微动力学模拟

Abstract: The superior activity of PdO_x catalysts for methane combustion is intimately linked to oxygen vacancies. However, a molecular-level understanding of how these defects govern the reaction under working conditions remains elusive. Here, we develop a novel “two site-pairs” microkinetic strategy integrated with density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations to unravel their role. AIMD simulations reveal the structural evolution from Pd(100) to a PdO(100) film and finally to the PdO(101) facet. DFT calculations identify Pd atoms adjacent to oxygen vacancies (Pdₒᵥ) as the primary active centers for facile CH₄ C–H bond cleavage on both PdOᵥ(101) and PdOᵥ(100) surfaces, while neighboring lattice oxygen atoms promote subsequent oxidation. This cooperative dual-site mechanism is central to the Mars-van Krevelen (MvK) pathway. Crucially, microkinetic modeling captures a temperature-driven switch in the dominant reaction mechanism: from the Langmuir-Hinshelwood mechanism prevalent on pristine PdO(101) to the Pdₒᵥ-mediated MvK mechanism that dominates on oxygen-deficient surfaces. The high activity of Pd_ov sites originates from their accessible frontier orbitals and the formation of covalent Pd_ov–C bonds in the transition states. Collectively, our work establishes a defect-mediated catalytic cycle, providing a fundamental basis for designing high-performance catalysts via oxygen vacancy engineering.

Key words: Methane oxidation, Pd-based catalysts, Oxygen vacancies, Density functional theory, Microkinetic modeling