Boosting the activity of transition metal carbides towards methane activation by nanostructuring

Abstract

The interaction of methane with pristine surfaces of bulk MoC and Mo₂C is known to be weak. In contrast, a series of X-ray photoelectron spectroscopy (XPS) experiments, combined with thermal desorption mass spectroscopy (TDS), for MoC_y (y = 0.5–1.3) nanoparticles supported on Au(111)—which is completely inert towards CH₄—show that these systems adsorb and dissociate CH₄ at room temperature and low CH₄ partial pressure. This industrially-relevant finding has been further investigated with accurate density functional theory (DFT) based calculations on a variety of MoC_y supported model systems. The DFT calculations reveal that the MoC_y/Au(111) systems can feature low C–H bond scission energy barriers, smaller than the CH₄ adsorption energy. Our theoretical results for bulk surfaces of Mo₂C and MoC show that a simple Brønsted–Evans–Polanyi (BEP) relationship holds for C–H bond scission on these systems. However, this is not the case for methane activation on the MoC_y nanoparticles as a consequence of their unique electronic and chemical properties. The discovery that supported molybdenum carbide nanoparticles are able to activate methane at room temperature paves the road towards the design of a new family of active carbide catalysts for methane activation and valorisation, with important implications in climate change mitigation and carbon cycle closure.