Facet Dependent Catalytic Activities of Anatase TiO$_2$ for CO$_2$ Adsorption and Conversion

TL;DR

This study investigates how different exposed facets of anatase TiO$_2$ influence CO$_2$ adsorption and conversion, revealing facet-dependent reactivity and mechanisms, including the role of water and surface reconstruction effects.

Contribution

It provides a detailed atomic-scale analysis of facet-dependent catalytic activities of anatase TiO$_2$ for CO$_2$ conversion using advanced simulations and models, highlighting new mechanistic insights.

Findings

(101) facet becomes more reactive with water presence.

Reconstruction reduces active sites by 75%.

Chemisorption can occur even with low binding energy.

Abstract

Understanding the atomic-scale interaction mechanism of CO$_2$ and H$_2$O on TiO$_2$ surface is crucial to establish a correlation between the catalytic efficiency with its exposed facet. Here, with the aid of a three-state model, nudged elastic band simulations, and DFT calculations, we examine the chemical restructuring of these molecules during the process of adsorption, coadsorption and conversion on (001) including (1$\times$4)-reconstructed, (010), and (101) facets of anatase TiO$_2$ and thereby, evaluate the step selective reactivity order. In addition, the results reveal the unexplored non-trivialities in the reaction mechanisms. For the most stable (101) facet, we show that the unfavorable carbonate complex formation becomes favorable by switching the reaction from endothermic to exothermic in the presence of water. Further, we find that small binding energy does not necessarily imply physisorption. It can also give rise to chemisorption, where the loss in energy due to repulsive Hartree and Madelung interactions is comparable to the energy gained through the chemical bonding. Such a scenario is demonstrated for the CO$_2$ adsorption on (010) and (101) facets. Though (001) remains the most reactive surface, if it undergoes reconstruction, which happens at ultra-high vacuum and high temperature, the number of active sites is reduced by three-fourths.