Structure and Stability of Oxyfluorides and Oxychlorides and Their Relations to Catalytic Activities in Oil Refining Reactions

Metal oxides have long been used as catalysts or supporters of catalysts in petroleum refining processes. Mixing anions such as fluorine into the structures of these compounds can greatly enhance their structural stability. Therefore, metal oxyfluorides are potential candidates for such catalysts due to their stability, atomic and electronic properties. The stability of several compositions of these compounds has been investigated, combining different anions or replacing them partially or fully. Since synthesizing mixed anion compounds is challenging, automatic crystal structure search together with density functional theory, particle swarm optimization algorithm and geometry relaxation calculations have been performed to obtain information regarding the stability and properties of these compounds. Plotting convex hull has revealed that FeOF, Fe₂OF₄, and AlOF have low formation energies, therefore can be used in synthesizing the catalyst materials. Based on structures obtained, electronic properties of these structures have been studied. Also, the effects of pressure on these compounds have been explored. Under pressures such as 10 GPa, fluorine rich compound Fe₂OF₄ and AlOF become highly destabilized, leaving FeOF more likely to be a candidate compound under higher pressures.