Methane activation and conversion on well-defined metal-oxide Surfaces: in situ studies with synchrotron-based techniques

Research focussed on in situ studies for the activation and conversion of methane on well-defined metal-oxide surfaces is reviewed. In recent years, experiments with single-crystal surfaces and well-ordered films have increased our understanding of the interaction of methane with solid surfaces. Late transition metals interact weakly with methane and elevated temperatures (>400 K) are necessary to enable a significant dissociation on the hydrocarbon. In contrast, an IrO₂(110) surface dissociates methane at temperatures below 200 K. Cooperative interactions between O and Ir are responsible for the binding of methane and the breaking of a C–H bond. This type of cooperative interactions involving O and a metal cation have also been seen on Ni/CeO₂(111) and Co/CeO₂(111) surfaces which dissociate methane at room temperature. Experiments of AP-XPS and in situ TR-XRD have shown that the active phase of metal/oxide catalysts used for the dry-reforming of methane frequently is a dynamic entity which evolves when the reaction conditions change. The addition of water to a mixture of CH₄/O₂ shifts the selectivity towards methanol production on CeO₂/CuO_x/Cu(111) and Ni/CeO₂(111) surfaces. Metal-support interactions and water site-blocking play a crucial role in the conversion of methane to methanol on these catalysts.