Computational modeling of bare, defective, and doped TiO2 surfaces and their role in the synthesis of ammonia

Titanium dioxide ﴾TiO2﴿ is a widely studied material characterized by its non‐toxicity, high abundance, and low cost. Moreover, that attractiveness of this solid comes from its application in photocatalytic process and photoelectrochemistry[1], such as hydrogen production and degradation of environmentally harmful compounds. Since late 70’ their catalytic activities were discovered and applied in many reactions, and it is nowadays one of the most used and studied catalysts. One of the most interesting application of TiO2 based materials is the fixation of nitrogen ﴾N2﴿ and its conversion to ammonia ﴾NH3﴿ at mild conditions [2] which contrast to the industrial Haber‐Bosch process that uses harsh conditions of temperature and pressure [3] and produces large amounts of CO2 [4] contributing to the global warming. Ammonia is an essential chemical compound for the synthesis of a variety of chemicals such as fertilizers, drugs, dyes and explosives, among others [3] TiO2 based materials were the first nitrogen fixation photocatalysts, and they have received great attention from the scientific community [2] Many of this attention throughout the years have come from the experimentalists, yet computational studies have started to emerge, as can be seen in few examples from the literature [3‐7] Another interesting feature of solid materials is that inclusion of dopants may increase reaction rates. In the case of N2 fixation and ammonia production with TiO2, it has been observed that doping with Mo increases the activity of the solid [4,8] Moreover, tantalum has been observed to activate N2 and produce ammonia as a single‐site solid catalyst [9,10] and as a gas phase cluster [11]

To understand the adsorption process of N2 and H-based species and their conversion to NH3 on selected bare and defective TiO2 surfaces (rutile 110 and anatase 101) to identify the key active sites and the possible reaction mechanisms by means of periodic DFT calculations.
To analyze the effects of Mo and Ta dopants on the relative reaction rates and mechanisms previously proposed.

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