This paper discusses our work in theory driven design of titania based nanocomposite oxides for the coupled thermo/photochemical activation of CO2. Density functional theory (DFT) simulations are carried out for small manganese oxide (MnOx) clusters on rutile and anatase TiO2 supports that are both hydroxylated and bare. Interesting effects include a change in the band gap of TiO2 that depends on the crystal form and hydroxylation state of TiO2. The Mn oxidation states in the supported clusters are also support dependent. We also observe support-specific effects on oxygen vacancy generation and the location of photogenerated electrons and holes. Finally, the possibility of activating CO2 by interaction with photogenerated electrons and thermally generated oxygen vacancies are examined. In parallel, the effects of MnOx modifications of TiO2 are explored experimentally. Supported MnOx materials are synthesized and characterized using different titania support phases and manganese precursors over a wide range of manganese surface loadings. X-ray diffraction results are consistent with well dispersed amorphous or very small crystalline MnOx domains. Diffuse reflectance UV-visible spectroscopy (DRUV-Vis) demonstrates a support- and precursor-specific red-shifted photoresponse in the MnOx-TiO2 materials relative to the bare supports. Temperature programmed reduction and oxidation cycles demonstrates the presence of redox active MnOx centers capable of reversible cycling at relatively low temperatures. Manganese oxidation states and coordination environments are also characterized using X-ray absorption spectroscopy. Initial results on CO2 activation are also presented. Experiment corroborates the predicted trends in behavior from DFT and identifies avenues for further exploration.

Theory driven design of MnOx-modified TiO2 for solar driven CO2 activation

249th National Meeting (2015)

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