Isolated Platinum Atoms in Ni/γ-Al₂O₃ for Selective Hydrogenation of CO₂ toward CH₄

Abstract

We introduce a catalyst composed of isolated Pt atoms surrounded by Ni atoms in a Ni–Pt alloy (iso-Pt), which was prepared on aluminum oxide (Al2O3) obtained by a simple impregnation method with typical hydrogen reduction pretreatment. This catalyst exhibited a relatively high CH4-formation rate while maintaining excellent selectivity for CH4 evolution, when compared to bulk Ni atoms (bulk-Ni), although bulk Pt atoms (bulk-Pt) produced CO rather than CH4. Kinetic studies revealed that one of the two roles of the iso-Pt species in the Ni–Pt alloy is to provide H2 dissociation sites at low temperature, resulting in high CO2 methanation activity. Fourier transform infrared spectroscopy clarified the second role of the iso-Pt species; tuning of the d-electronic state by alloying to surrounding Ni atoms leads to CO molecules that are strongly anchored to the iso-Pt atoms, which weakens the C–O bond of the CO species attached to the Pt atoms and improves the abilities of the surrounding Ni atoms to promote further methanation with hydrogen.