S. Ted Oyama

Chemical and Catalytic Properties of Ozone

IV. SURFACE REACTIONS AND CATALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 A. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 B. Ozone Adsorption and Reaction with Adsorbates . . . . . . . . . . . . . . . . . . . 296 C. Liquid-Phase Catalytic Oxidations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 D. Gas-Phase Catalytic Oxidations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 E. Gas-Phase Catalytic Ozone Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . 306 F. Reactions with Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 G. Technology for Catalytic Ozone Treatment of Polluted Airstreams . . . . 309

Review of the synthesis of layered double hydroxides: a thermodynamic approach

The synthesis of layered double hydroxides (LDHs) by hydrothermal-LDH reconstruction and coprecipitation methods is reviewed using a thermodynamic approach. A mixture model was used for the estimation of the thermodynamics of formation of LDHs. The synthesis and solubility of LDHs are discussed in terms of standard molar Gibbs free energy change of reaction. Data for numerous divalent and trivalent metals as well as for some monovalent and tetravalent metals that may be part of the LDH structure have been compiled. Good agreement is found between theoretical and experimental data. Diagrams and tables for the prediction of possible new LDH materials are provided.

Decomposition of ozone using carbon-supported metal oxide catalysts

Abstract Ozone decomposition was investigated over a series of activated carbon-supported oxide catalysts deposited on cordierite foam substrates. Emphasis was placed on the study of binary oxide combinations formed from MnO 2 , Co 3 O 4 , Fe 2 O 3 and NiO, the most active transition-metal single oxides for the reaction. The MnO 2 –Fe 2 O 3 system showed the highest ozone decomposition activity. Laser Raman results under ambient and dehydrated conditions suggested an interaction between MnO 2 and Fe 2 O 3 . The introduction of organic and inorganic binders increased both the physical stability and activity of the catalysts.

Crystal structure and chemical reactivity of transition metal carbides and nitrides

Trends in melting points, stoichiometry, and crystal structures in early transition metal carbides and nitrides are discussed in terms of the Engel-Brewer valence bond theory. It is deduced that carbon and nitrogen combine their valence sp electrons with the metal spd bands. As a consequence crystal structure and chemical reactivity of the compounds resemble those of elements further to the right in the Periodic Table. This is in accord with the original suggestion of Levy and Boudart

Structure and dispersion of molybdenum oxide supported on alumina and titania

Samples of molybdenum oxide supported on alumina and titania have been studied by oxygen chemisorption, X-ray diffraction and laser Raman spectroscopy. The three techniques gave a consistent picture of the dispersion of molybdenum oxide on the supports. For the alumina-supported samples it was found that reduction and reoxidation at 673 K were appropriate for titrating surface molybdenum atoms. This temperature was found to be lowered to 623 K for the titania-supported materials. The structure of the dispersed phase on both supports was found to be the same. In the absence of water, it consisted of a monomeric OMoO4 species with a single OMo double bond, four O—Mo links to the surface, and a possible long O⋯Mo bond opposite the double bond. With the introduction of water vapour, this species became a dioxo species with two OMo double bonds and two O—Mo links to the surface. The interaction of the oxide with the support was of an acid–base nature.

Supported nickel catalysts for carbon dioxide reforming of methane in plug flow and membrane reactors

Abstract The catalytic production of synthesis gas through methane reforming using carbon dioxide was studied in a plug flow reactor and a membrane reactor at atmospheric pressure over nickel supported on MgO and La 2 O 3 . The Ni 0.03 Mg 0.97 O and the Ni/La 2 O 3 catalysts exhibited high activity and gave conversions of methane at equilibrium levels in the plug flow mode of operation. Incorporation of a Vycor glass membrane in the reactor resulted in higher conversions than obtained in an identical plug flow reactor operated without diluent. The catalysts had low to moderate surface areas and low uptakes of H 2 and CO at room temperature. X-ray diffraction showed that there was no discernable change between the catalysts before and after reaction. Elemental analysis showed that there was little carbon deposited on the Ni 0.03 Mg 0.97 O catalyst but there was slight coking on the Ni/La 2 O 3 catalyst.

Synthesis of high surface area vanadium nitride

Abstract Fine vanadium nitride powders (particle size 11 nm) have been prepared by temperature programmed reduction and nitridation of V 2 O 5 by gaseous ammonia. The reaction was followed by monitoring gas phase reaction products by on-line mass spectroscopy. X-ray diffraction and elemental analysis were used to identify various solid-state reaction intermediates, V 6 O 13 , V 2 O 4 , VO 2 , V 2 O 3 , and VO, and to establish that the final reaction step was the nitridation of VO to VN. Heating rate had a substantial effect on product specific surface area and a rate of 0.083 K sec −1 resulted in an optimal value of 90 m 2 g −1 . The activation energy for nitridation was not constant, but rose from 203 to 243 kJ mol −1 as the extent of reaction increased from 0.25 to 0.75. The transformation was limited by the bulk diffusion of oxygen and nitrogen and not by a surface process.

Preparation and hydrodenitrogenation performance of rhenium nitride

This paper describes the preparation of rhenium nitride and its behavior in hydrodenitrogenation. Hydrodenitrogenation of quinoline was measured at 3.1 MPa between 523 and 613 K, and compared to rhenium metal and rhenium sulfide. The rhenium sulfide had the best catalytic performance of the three samples. X-ray photoelectron spectroscopy and X-ray diffraction revealed that, after reaction, the rhenium nitride surface was similar to the rhenium metal surface.

Absolute determination of reaction mechanisms by in situ measurements of reaction intermediates

This paper presents a general methodology to determine reaction mechanisms using in situ measurement of concentration and reaction rate of intermediates. The criteria for testing the validity of a reaction sequence are discussed. An example is given for a heterogeneous catalytic reaction, the decomposition of ozone on manganese oxide.

SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF TUNGSTEN OXYNITRIDE

High surface area tungsten oxynitride has been prepared by the temperature programmed reaction (TPR) of WO 3 with NH 3 . All samples were characterized by x-ray diffraction (XRD), nitrogen physisorption, CO chemisorption, and elemental analysis. Samples were prepared at different heating rates (β), and a Redhead analysis yielded an activation energy for nitridation of 109 kJ mol −1 . A heating rate of 0.016 K s −1 gave optimal synthesis conditions. Solid state intermediates were studied by interrupting the temperature program at various stages. No distinct suboxide phases were found using XRD. The nitridation step was determined to be a continuous transformation from oxide to oxynitride. Surface area, CO uptake, and nitrogen weight % were all found to increase as the reaction progressed. Reactivity experiments showed reasonable hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) activity, but little hydrogenation (HYD) or hydrodesulfurization (HDS) activity.