(544dj) Theoretical Investigation of CO Adsorption and Disproportionation on Mo2C Nanotube Supported Pt Nanoparticles

Our recent experimental work on CO reactions on Mo₂C nanotube supported Pt nanoparticles (NPs) under TAP condition shows the formation of CO₂ via the process of CO disproportionation (ACS Appl. Mater. Interfaces 2017, 9, 9815). Different amount of deposited Pt NPs results to different behavior of CO adsorption and disproportionation (Boudouard reaction). In this work, the reaction mechanism and the role of Pt nanoparticles are corroborated theoretically with the periodic density functional theory (DFT) method. The XRD patterns of Mo₂C nanotube corresponds to the pure hexagonal phase of Mo₂C (β-Mo₂C). The β-Mo₂C (100) surface was selected to model the Mo₂C nanotube as the lattice fringes are in the direction of (100) plane. We studied the potential energy surfaces of Boudouard reaction (2CO → CO₂ + C) on Mo₂C (100) surface, Pt (111) surface and Pt/Mo₂C interface. CO dissociation readily occur on Mo₂C (100) surface, but not on Pt (111) surface as the former is exothermic and the latter is endothermic. CO₂ is produced from the surface O from CO dissociation reacting with a second CO. C atoms poison the active sites on Mo₂C (100) surface. At Pt/Mo₂C interface, CO dissociation is still exothermic, however, with a larger activation energy. C adsorption prefers the Pt sites instead of the Mo sites. Boudouard reaction takes place on the Mo₂C region and the deposited Pt NPs collect the C atoms, ‘helping’ the active Mo sites for further CO₂ formation. Our simulation results are consistent with the experiment.