Fundamental analysis for active phase of rutile-based IrO2 catalyst: Comparison study of CH4 oxidation on IrO2(100) and IrO2(110)

Highlight • IrO2(1 0 0) provides the high stability of adsorbed CH4. • IrO2(1 0 0) can activate methane at low temperature (∼100 K). • CH4 complete oxidation is also found to be facile on IrO2(1 0 0). • IrO2(1 0 0) surface is active toward CH4 oxidation, but it is not active as IrO2(1 1 0). • (1 1 0) is not an only active facet determining the reactivity of rutile IrO2 catalyst; the (1 0 0) surface is also active. This study examined the reactivity of IrO2(1 0 0) toward CH4 oxidation and compared the reactivity with the IrO2(1 1 0) surface to obtain fundamental insights of the active phase for rutile structure-based IrO2 catalyst. Our DFT simulation predicted that stoichiometric IrO2(1 0 0) surface stabilizes and easily activates the adsorbed CH4. The subsequent reactions toward complete oxidation are also facile with the predicted rate-limiting steps from CH2O to CO. Similar kinetic behavior was predicted from CH4 oxidation on an oxygen-rich IrO2(1 0 0) surface, but it is more reactive than the stoichiometric IrO2(1 0 0) surface. The simulated TPRS results confirmed that the (1 1 0) facet is more active than (1 0 0); CH4 conversions on the (1 0 0) surface are predicted to be ∼ 35 % lower than on the (1 1 0) surface. Based on these results, the IrO2(1 0 0) surface is expected to be active toward CH4 oxidation but not as active as IrO2(1 1 0). Overall, the (1 1 0) surface is not the only active facet determining the reactivity of the rutile IrO2 catalyst; the (1 0 0) surface is also active. The comparison results from the current study would provide fundamental insights into the active phase of rutile structure-based IrO2 catalyst.