Surface frustrated Lewis pairs in titanium nitride enable gas phase heterogeneous CO2 photocatalysis
Yunjie Zou, Chengliang Mao, Mingkai Xu, Chao Xing, R. L. Wang, Geoffrey A. Ozin, Lan Ling
Abstract
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 (TiNxOy) 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 TiNxOy alone, as well as conventional platinum supported metal oxides. Heterogeneous surface frustrated Lewis pairs catalysis have been predominantly focused on metal oxide hydroxides. This study instead explores a different chemical composition space by shifting from metal oxides to metal nitrides for CO2 photoreduction.