Cooperatively enhanced catalytic properties of Ti@Al(100) near-surface alloy for aluminum hydrogenation

• Effects of different doping configurations and concentrations are studied in detail.
• The single atom, (0,2) pair and [0,2] domain of Ti doping are preferred.
• Kubas-type σ back-bonding interaction accounts for the enhanced catalytic properties.
• The improved activity of Al due to Ti doping beneath it contributes to H2 splitting.
• The cooperatively enhanced catalytic properties are confirmed in doping domain.

We have carried out detailed first-principles studies of the catalytic properties of Ti@Al(100) near-surface alloy. The single Ti atom, (0,2) Ti–Ti pair, and [0,2] Ti doping domain have better catalytic performances. These species doped in the top surface can develop back-bonding interaction with H2 to catalyze the splitting, which however on the other hand hinder the dissociated H atoms to diffuse. Doped in the subsurface, they can also enhance hydrogen interaction on aluminum to catalyze H2 splitting. The activation energies are 0.80, 0.68, and 0.48 eV for Ti atom, (0,2) pair, and [0,2] doping domain, respectively. Without Ti–H bond, the dissociated H atom could diffuse away with small energy cost. The structural expansion induced by titanium doping, the lower electronegativity of Ti, and the more valence electrons of Ti may cooperatively facilitate the charge transfer from the above Al atoms to H2 molecule, accounting for the enhanced splitting properties.

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