Spot the difference: hydrogen adsorption and dissociation on unsupported platinum and platinum-coated transition metal carbides.

Abstract

Hydrogenation reactions are involved in several processes in heterogeneous catalysis. Platinum is the best-known catalyst; however, there are limitations to its practical use. Therefore, it is necessary to explore alternative materials and transition metal carbides (TMCs) have emerged as potential candidates. We explore the possibility of using cheap TMCs as supports for a Pt monolayer, aiming to reduce the amount of the noble metal in the catalyst without a significant loss of its activity towards H2 dissociation. Hence, analyzing H2 dissociation from a fundamental point of view is a necessary step towards a further practical catalyst. By means of periodic DFT calculations, we analyze H2 adsorption and dissociation on Pt/β-Mo2C and Pt/α-WC surfaces, as a function of hydrogen surface coverage (ΘH), resembling a more realistic model of a catalyst. H2 dissociation rates were analyzed as a function of the reaction temperature. The results show that Pt/C-WC and Pt/Mo-Mo2C have a Pt-like behavior for H2 dissociation at ΘH > 1/2 ML. At a particular temperature of 298 K, Pt/C-WC and Pt/Mo-Mo2C have low energy barriers for H2* → 2H* (0.13 and 0.11 eV, respectively), close to the value of Pt (0.06 eV). For the highest coverage, i.e. ΘH = 1, Pt/C-WC has a lower activation energy and a higher reaction rate than Pt. Finally, the H2 dissociation rate is higher in Pt/Mo-Mo2C than in Pt when increasing the temperature above 298 K. Our results put Pt/C-WC and Pt/Mo-Mo2C under the spotlight as potential catalysts for H2 dissociation, with a similar performance to Pt, paving the way for further experimental and/or theoretical studies, addressing the capability of Pt/TMC as practical catalysts in hydrogenation reactions.