(624h) Controlling Methane Activation for Selective Production of Value-Added Chemicals Using Ir-Doped RuO2(110) and IrO2(110) Nanoscopic Islands on RuO2(110)

Converting methane to value-added chemicals is a promising approach for sustainable energy utilization. However, the challenges lie in breaking the strong C–H bonds of methane and controlling subsequent reactions to achieve desired product selectivity. IrO₂(110) has shown high reactivity for methane activation at low temperatures (< 100 K), but it mainly produces complete oxidation products (CO₂ and H₂O) [1]. Density functional theory (DFT) calculations indicate that CH₄ molecules form strong dative bonds with coordinatively unsaturated Ir atoms (Ir_cus), requiring more energy for desorption than for activation. While rutile RuO₂(110) is less active, its structural similarity to IrO₂ suggests the possibility of synthesizing mixtures of IrO₂. This study aims to elucidate the effects of Ir isolation on methane activation by performing DFT calculations on Ir-doped RuO₂ and IrO₂ islands on RuO₂ catalysts. We evaluate the binding energies of CH₄*, CH₃*, H*, CO*, O*, OH*, and H₂O* on these surfaces and calculate methane oxidation pathways to form products such as C₂H₄, CH₂O, and CO₂. Our findings indicate that, in general, the binding energies of species are most negative on pure IrO₂, becoming less negative on Ir-doped and Ir monolayered RuO₂, and further less negative on IrO₂ islands on RuO₂. Similarly, the binding energies on Ru_cus from pure RuO₂ shows more negative values than Ru_cus at interfacial sites of IrO₂ islands on RuO₂. For example, the CO binding energies for the surfaces are as follows: -224 kJ/mol (pure IrO₂), -206 kJ/mol (Ir single atom in RuO₂), -202 kJ/mol (IrO₂ monolayer on RuO₂), -177 kJ/mol (IrO₂ islands on RuO₂), -150 kJ/mol (pure RuO₂), and -113 kJ/mol (Ru sites at the interface between IrO₂ islands and RuO₂). Therefore, leveraging the different features of Ir_cus and Ru_cus in different environments may enable cost-effective methane conversion.