Surface frustrated Lewis pairs in titanium nitride enable gas phase heterogeneous CO₂ photocatalysis

Gas-phase heterogeneous catalytic CO₂ hydrogenation to commodity chemicals and fuels via surface frustrated Lewis pairs is a growing focus of scientific and technological interest. Traditional gas-phase heterogeneous surface frustrated Lewis pair catalysts primarily involve metal oxide-hydroxides (MOH•••M). An avenue to improve the process performance metrics lies in replacing the Lewis base MOH with a stronger alternative; an intriguing example being the amine MNH₂ in metal nitrides. This study establishes a proof-of-concept that an amine-type photoactive surface frustrated Lewis pair (MNH₂•••M) can be constructed in titanium nitride (TiN_xO_y) when integrated with a nanoscale platinum spillover co-catalyst. This surface frustrated Lewis pair, comprising Ti-NH₂ as the Lewis base and low-valent Ti as the Lewis acid, facilitates the gas-phase light-assisted heterogeneous reverse water-gas shift reaction. The reaction proceeds via a surface-active carbamate intermediate, Ti-(H₂N-COO)-Ti, whereby the synergism of Lewis acidic and Lewis basic sites endows it with superior performance indicators compared to TiN_xO_y alone, as well as conventional platinum supported metal oxides.