Origin of enhanced toluene hydrogenation by Pt–Ru catalysts for an efficient liquid organic hydrogen carrier

Novel catalysts for efficient formation of liquid organic hydrogen carriers (LOHCs) used in hydrogen storage and transport show great promise. Although Pt–Ru alloys have exhibited catalytic activities superior to those of Pt in the hydrogenation of toluene to methylcyclohexane, the origins are still unclear. Herein, we use density functional theory (DFT) to examine the mechanisms for toluene hydrogenation on Pt and various Pt–Ru bimetallic catalysts. The core@shell-type Ru@Pt(111) shows more thermodynamically and kinetically favored hydrogenation of toluene than pure Pt or Pt–Ru ordered structures. The origin of the improved catalytic activity on Ru@Pt(111) is examined by separating the strain and ligand effects between the core and shell layers. The ligand effect lowers the d-band center more pronouncedly; moreover, the favorable charge gain on the surface lowers the binding energies of reaction intermediates as well as the activation energies for each hydrogenation step. This work provides insight into the design of novel catalysts providing LOHCs for efficient hydrogen storage.