The exceptional activity of IrO2(110) for CH4 C-H cleavage as well as its ability to stabilize CHx groups over a wide temperature range provide motivation for investigating methane oxidation on IrO2(110) under catalytic conditions. In this talk I will discuss recent first-principles microkinetic simulations of the catalytic oxidation of CH4 on IrO2(110) and their accuracy in reproducing measurements of the catalytic kinetics as well as species coverages determined using operando x-ray photoelectron spectroscopy (XPS). Our kinetic studies show that IrO2(110) films are highly active for the catalytic combustion of CH4 at moderate temperatures (~500-650 K), and measurements using near-ambient pressure, synchrotron XPS demonstrate that high coverages of OH groups and CHyO2 species form on IrO2(110) during catalytic CH4 oxidation at all conditions studied. Using density functional theory (DFT), we identified two general pathways for CH4 oxidation to CO2 involving either an adsorbed CO or a CHO2 intermediate. A microkinetic model developed from our DFT calculations reproduces key aspects of the catalytic kinetics and the coverages of adsorbed intermediates measured experimentally. The model predicts that catalytic CH4 oxidation on IrO2(110) occurs almost entirely by a CO-mediated pathway, while competing pathways generate CHO2 species that inhibit CH4 oxidation. Our study provides molecular-level insights about the dominant reaction pathways and the roles of various adsorbed species in mediating catalytic CH4 oxidation on IrO2(110), and highlights the utility that operando surface spectroscopy can play in developing first principles models of catalytic reaction kinetics.

Linking operando spectroscopy with microkinetic modeling to unravel the catalytic mechanism for CH4 oxidation on IrO2(110)

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