Molybdenum carbide supported metal catalysts (Mn/MoxC; M = Co, Ni, Cu, Pd, Pt) – metal and surface dependent structure and stability

Abstract

The surface and metal-dependent morphologies and energies of molybdenum carbide supported metal catalysts (M_n/Mo_xC; M = Co, Ni, Cu, Pd, Pt) have been systematically investigated on the basis of periodic density functional theory computations. On the hexagonal Mo₂C phase, metallic Mo₂C(001) prefers dispersion at very low loading for Co and Ni, up to high loading for Pd and Pt; but only aggregation for Cu. On Mo/C-mixed Mo₂C(101), all metals prefer dispersion up to high loading and aggregation at very high loading. On cubic Mo/C-mixed δ-MoC(001), all metals prefer aggregation up to high loading and three-dimensional clusters at very high loading. On Mo₂C(001), all adsorbed metals are negatively charged, while on Mo₂C(101) and MoC(001), Co, Ni and Cu are positively charged, and Pt is negatively charged, while Pd is nearly neutral. On all three surfaces, the adsorption of these metals is favored thermodynamically. Although correlation between electron transfer and adsorption energy has been found, no correlations between the adsorption energy (and electron transfer) and electronegativity (and ionization potential and electron affinity) of the atoms can be estimated. These results provide a basis for the study and design of size- and shape-dependent (single-atom, nanocluster and nanoparticle) catalysts and their respective associated catalytic processes.