Screening and Discovery of Metal Compound Active Sites for Strong and Selective Adsorption of N₂ in Air

Abstract

Photocatalytic nitrogen fixation has the potential to provide a greener route for producing nitrogen‐based fertilizers under ambient conditions. Computational screening is a promising route to discover new materials for the nitrogen fixation process, but requires identifying "descriptors" that can be efficiently computed. In this work, we argue that selectivity toward the adsorption of molecular nitrogen and oxygen can act as a key descriptor. A catalyst that can selectively adsorb nitrogen and resist poisoning of oxygen and other molecules present in air has the potential to facilitate the nitrogen fixation process under ambient conditions. We provide a framework for active site screening based on multifidelity density functional theory (DFT) calculations for a range of metal oxides, (oxy)borides, and (oxy)phosphides. The screening methodology consists of initial low‐fidelity fixed geometry calculations and a second screening in which more expensive geometry optimizations were performed. The approach identifies promising active sites on several TiO2 polymorph surfaces and a VBO4 surface, and the full nitrogen reduction pathway is studied with the BEEF‐vdW and HSE06 functionals on two active sites. The findings suggest that meta‐stable TiO2 polymorphs may play a role in photocatalytic nitrogen fixation, and that VBO4 may be an interesting material for further studies.

Assessing Exchange-Correlation Functionals for Heterogeneous Catalysis of Nitrogen Species

“…In addition, rev-vdW-DF2 and BEEF-vdW can be accurate because of the small error in adsorption energy (RMSE of 0.261 and 0.238 eV, respectively) and ammonia synthesis reaction (error of −0.055 and 0.109 eV, respectively). Another important case is TiO 2 , which has been extensively studied for photocatalytic ammonia synthesis. ,− In most cases, the BEEF-vdW adsorption energies are similarly accurate to hybrid functionals, although there is a substantial deviation for CN adsorption, where the error of BEEF-vdW and other GGA functionals is ∼1 eV. This suggests that hybrid calculations may be necessary for evaluating carbon-assisted pathways, , and that the HSE06-D3 or PBE0-D3 adsorption energies of NH x species can be considered accurate despite the large error in the gas-phase ammonia synthesis reaction.…”