Catalytic Ammonia Synthesis over Pure, Defective, and Metal-Doped Rutile TiO2: A Periodic DFT Study

TL;DR

This study uses computational methods to explore how metal-doped titanium dioxide surfaces can efficiently produce ammonia from nitrogen and water.

Contribution

The novel contribution is identifying that doping vacant sites with Mo or Ta significantly lowers reaction energy barriers for ammonia synthesis.

Findings

Doping TiO2 surfaces with Mo or Ta reduces the energy of reaction intermediates, improving catalytic efficiency.

Doping vacant Ti6c sites has a stronger effect on reaction energetics than exposed Ti5c sites.

Higher dopant concentration on vacant sites further decreases intermediate energies, enhancing ammonia synthesis.

Abstract

In this work, we
aim to describe the energetics associated with
the formation of ammonia from N2 interacting with doped
hydroxylated rutile TiO2(110) surfaces with the vacant
O2c site, following the reaction N2 + 3H2O → 2NH3 + 3/2O2. The water molecules
interact with the surface, creating exposed Ti–OH groups that
can transfer hydrogen to the adsorbed N2 molecule. Two
metal dopants are evaluated: Mo and Ta. For both metals, calculations
show a dramatic decrease in the energy of most intermediates during
the entire mechanism, leading to more favorable reaction mechanisms.
Nonetheless, it is worth noting that when the Ti6c site
of the vacant site is doped with either Mo or Ta, there is a stronger
effect on the energetics than doping on the exposed Ti5c sites. The effect of increasing the concentration of metal dopants
on the vacant site was also investigated. In this case, calculations
indicate that a higher percentage of the dopant on the surface results
in a more substantial decrease in the energy of most intermediates,
suggesting that increasing the dopant content could be beneficial
for the catalytic process.

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