Composition and structure of the RuO2(110) surface in an O2 and CO environment: implications for the catalytic formation of CO2

The phase diagram of surface structures for the model catalyst RuO2(110) in contact with a gas environment of O2 and CO is calculated by density-functional theory and atomistic thermodynamics. Adsorption of the reactants is found to depend crucially on temperature and partial pressures in the gas phase. Assuming that a catalyst surface under steady-state operation conditions is close to a constrained thermodynamic equilibrium, we are able to rationalize a number of experimental findings on the CO oxidation over RuO2(110). We also calculated reaction pathways and energy barriers. Based on the various results the importance of phase coexistence conditions is emphasized as these will lead to an enhanced dynamics at the catalyst surface. Such conditions may actuate an additional, kinetically controlled reaction mechanism on RuO2(110).Comment: 12 pages including 8 figure files. Submitted to Phys. Rev. B. Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

A new class of highly dispersed VOx catalysts on mesoporous silica: Synthesis, characterization, and catalytic activity in the partial oxidation of ethanol

The morphology of vanadium oxide supported on a titania-modified mesoporous silica (MCM-41), obtained by means of a careful grafting process through atomic layer deposition, was studied using a variety of characterization techniques. The X-ray diffraction (XRD) together with transmission electron microscopy (TEM), V-51 nuclear magnetic resonance (V-51-NMR), Raman, FTIR and DRS-UV/Vis results showed that the vanadia species are extremely well dispersed onto the surface of the mesoporous support; the dispersion being stable upon thermal treatments up to 400 degrees C. Studies of the catalytic activity of these materials were performed using the partial oxidation of ethanol as a probe reaction. The results indicate an intrinsic relationship between dispersion, the presence of a TiO2-VOx phase, and catalytic activity for oxidation and dehydration. (c) 2005 Elsevier B.V. All rights reservedclose283

Ionizing radiation induced catalysis on metal oxide particles. 1998 annual progress report

'High-level radioactive waste storage tanks within DOE sites contain significant amounts of organic components (solid and liquid phases) in the form of solvents, extractants, complexing agents, process chemicals, cleaning agents and a variety of miscellaneous compounds. These organics pose several safety and pretreatment concerns, particularly for the Hanford tank waste. Remediation technologies are needed that significantly reduce the amounts of problem organics without resulting in toxic or flammable gas emissions, and without requiring thermal treatments. These restrictions pose serious technological barriers for current organic destruction methods which utilize oxidation achieved by thermal or chemical activation. This project focuses on using ionizing radiation (a,b,g) to catalytically destroy organics over oxide materials through reduction/oxidation (redox) chemistry resulting from electron-hole (e{sup -}/h{sup +}) pair generation. Conceptually this process is an extension of visible and near-UV photocatalytic processes known to occur at the interfaces of narrow bandgap semiconductors in both solution and gas phases. In these processes, an electron is excited across the energy gap between the filled and empty states in the semiconductor. The excited electron does reductive chemistry and the hole (where the electron was excited from) does oxidative chemistry. The energy separation between the hole and the excited electron reflects the redox capability of the e{sup -}/h{sup +} pair, and is dictated by the energy of the absorbed photon and the bandgap of the material. The use of ionizing radiation overcomes optical transparency limitations associated with visible and near-UV illumination (g-rays penetrate much farther into a solution than UV/Vis light), and permits the use of wider bandgap materials (such as ZrO{sub 2}) which possess potentially greater redox capabilities than those with narrow bandgap materials. Experiments have been aimed at understanding the mechanism(s) of g-radiocatalysis and extending the body of knowledge about e{sup -}/h{sup +} pair chemistry of semiconducting metal oxide (MO) materials by examining the influence of surface structure, defects and dopants on the photocatalytic activity of narrow bandgap materials (TiO{sub 2}). An outcome of this proposed work will be a more thorough evaluation of the use of ionizing radiation in the catalytic remediation of organics (and other problem species) in high-level mixed waste.