(504h) A Theoretical Examination of Nitrogen Photofixation on Rutile TiO2(110)

The photofixation of nitrogen is a promising reactive process for creating distributed production of nitrates and ammonia requiring only ambient conditions. The reaction has been demonstrated experimentally over titania catalysts as early as the 1970's, and can produce both oxidized and reduced compounds. Amazingly, this reaction proceeds at room temperature and pressure and only requires nitrogen, water, and light. This work has clear commercial potential, and beyond industry such benign process conditions would allow nitrogen products to be made in a more distributed way, decreasing the carbon emissions from transportation and facilitating improved management of fertilizer application. However, despite it's age and clear benefits, little fundamental work has been done on this system and currently only low reaction rates have been achieved. Gaining theoretical understanding of the mechanism of the reaction will enable optimization of the active site and mechanism of the process. In this talk we discuss the mechanistic challenges of nitrogen photofixation over titania, and present ab initio calculations for the screening of possible active sites based on a tradeoff of stability and reactivity. The potential roles of defect sites and impurities are also discussed, and we hypothesize that the process occurs over meta-stable active sites that are generated by reactions of impurities and photo-generated holes. These findings address several inconsistencies in the literature, and suggest new strategies for the rational design of more efficient nitrogen photofixation catalysts.