Diversity of Adsorbed Hydrogen on the TiC(001) Surface at High Coverages

The catalyzed dissociation of molecular hydrogen on the surfaces of diverse materials is currently widely studied due to its importance in a broad range of hydrogenation reactions that convert noxious exhaust products and/or greenhouse gases into added-value greener products, such as methanol. In the search for viable replacements for expensive late-transition-metal catalysts, TiC has been increasingly investigated as a potential catalyst for H₂ dissociation. Here, we report on a combination of experiments and density functional theory calculations on the well-defined TiC(001) surface, revealing that multiple H and H₂ species are available on this substrate, with different binding configurations and adsorption energies. Our calculations predict an initial occupancy of H atoms on the surface C atom sites, which then enables the subsequent stabilization of H atoms on top of the surface Ti atoms. Further H₂ can be also molecularly adsorbed over Ti sites. These theoretical predictions are in full accordance with information extracted from X-ray photoemission spectroscopy and temperature-programmed desorption experiments. The experimental results show that at high coverages of hydrogen, there is a reconstruction of the TiC(001) surface, which facilitates the binding of hydrogen.