Active Pt Thin Layers over MoC for the Low-Temperature Water-Gas Shift Reaction

Abstract

Pt/MoC catalysts have been documented to be highly active for the water-gas shift reaction at low temperatures, but identification of the active metal entity remains challenging primarily because of the co-existence of metal nanoparticles, clusters and single-atoms in the catalysts. Here, Pt dispersion on MoC was finely tuned by the carburization of a Pt/MoO3 precursor with a CH4/H2 mixture at 873–973 K. It was found that the 3 nm Pt particles over MoO3 redispersed into thin layers (mainly bilayers/trilayers) at 873 K while loosely-arranged monolayers/single-atoms at 973 K during the carburization of MoO3 to MoC. Tests for the low-temperature water-gas shift reaction found that Pt thin layers showed the most pronounced activity based on the moderate adsorption of CO on Pt and the facile dissociation of water over MoC at their interfacial perimeter. But the activity lowered as Pt further dispersed into monolayers/single-atoms in the Pt/MoC catalysts. In situ IR experiments revealed that the Pt thin layers facilitated the adsorption of CO while the MoC support dissociated H2O into reactive –OH species that might migrate to Pt and react with CO, expediting the low-temperature WGS reaction.