Oxide chemistry and catalysis

Abstract

Metal oxides are among the most earth abundant resources on the planet. For example, by mass, Fe is the most earth abundant element, Ni is the sixth most abundant, and Al is the eighth most abundant. Like Fe, Ni, and Al, most metals with only a very few exceptions exist as oxides under ambient conditions. Even for the simplest binary metal oxides, a large number of phases and oxidation states can exist depending on the oxygen chemical potential, and this phase space rapidly expands when considering ternary and higher order oxides, doped materials, and metal/metal oxide interfaces. Questions of electronic and crystal structures become even more complicated at a surface or interface compared to the bulk material. This is, in part, because defects and impurities often segregate to surfaces. Surfaces are also accessible for molecular adsorption and interfacial bonding, which require challenging interface-specific spectroscopies to accurately characterize. Additionally, surfaces lack the periodicity of bulk crystals, making them challenging to treat theoretically. Metal oxides are also inherently reactive and can serve as catalysts for numerous reactions. Additionally, high surface area mesoporous oxides often act as supports for metal nanoparticles or other co-catalysts. In such cases, the oxide framework can modulate the activity of the supported catalyst through strong metal support interactions. In many cases, metal oxides are semiconducting and exhibit strong absorption coefficients for visible light, making these materials attractive for applications in photocatalysis, solar energy conversion, and storage. The highly polar bonds in many metal oxides result in strong electron–phonon coupling, making it difficult to decouple the electronic and nuclear contributions to the wavefunction. This strong coupling gives rise to unique electrical and optical properties, which often dominate electron transport and significantly complicate excited state modeling. All these effects point to the need for chemical physics to provide a fundamental framework required to support the many promising applications of oxide chemistry and catalysis.