Replacing bulk Pt in Pt-Ni-Pt bimetallic structures with tungsten monocarbide (WC): Hydrogen adsorption and cyclohexene hydrogenation on Pt-Ni-WC

It is well known that bimetallic surfaces, such as the Pt-Ni-Pt(bulk) structure, with one monolayer of Ni residing in the subsurface region of Pt, often show unique catalytic properties including low temperature hydrogenation pathways. It is also known that transition metal carbides, such as tungsten monocarbide (WC), often show catalytic properties similar to Pt. In the current study, we explored the possibility to replace bulk Pt in the Pt-Ni-Pt(bulk) structure by anchoring Pt-Ni on a WC substrate. The dissociative adsorption of hydrogen and the hydrogenation of cyclohexene were used as probe reactions to evaluate the chemical properties of Pt-Ni-WC(bulk), with Density Functional Theory (DFT) calculations and Temperature Programmed Desorption (TPD) measurements being performed. Similar to Pt-Ni-Pt, the Pt-Ni-WC surface shows weakly bonded hydrogen as predicted from DFT calculations and confirmed by TPD experiments. In addition, the presence of weakly bonded atomic hydrogen and cyclohexene led to the low temperature hydrogenation of cyclohexene, again similar to that observed on Pt-Ni-Pt. Our results indicate that anchoring the Pt-Ni structure on WC should potentially reduce the loading of Pt in the bimetallic catalysts. Furthermore, the replacement of bulk Pt by WC should also prevent the diffusion of the subsurface Ni into the bulk, potentially increasing the stability of the desirable subsurface bimetallic structure in Pt-Ni-WC. (C) 2010 Elsevier Inc. All rights reserved.