IR spectroscopic investigations of chemical and photochemical reactions on metal oxides: bridging the materials gap.

In this review, we highlight recent progress (2008-2016) in infrared reflection absorption spectroscopy (IRRAS) studies on oxide powders achieved by using different types of metal oxide single crystals as reference systems. Precise polarization- and azimuth-dependent IRRAS data recorded for single crystal substrates has allowed for fundamental insights into the surface chemistry and photochemistry of numerous probe molecules on various surfaces exposed by three very important metal oxides (ZnO, TiO2, and CeO2). When using carbon monoxide (CO) as a probe molecule, deep insight into the role of defects in the surface chemistry of oxides can be gained, as will be demonstrated by the characterization of different imperfections (e.g., O vacancies, nanofacets) present at oxidic samples. In addition, photostimulated excitations, e.g., electron or hole polaronic trap states, can be studied using IR-spectroscopy. Reliable and comprehensive reference data acquired for different oxide monocrystal model systems enables atomic-level insights into the structural, electronic, and reactive properties of the substantially more complex nanostructured oxide particles. We foresee that future application of IR spectroscopy to other challenging systems, including polar oxide surfaces with their often complex reconstruction patterns and oxide-supported highly dispersed metal particles, will provide a major advancement in the understanding of heterogeneous catalysts (539 references).