Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Catalytic Properties of Ceria and CeO2-Containing Materials

https://dspace.library.uu.nl/bitstream/handle/1874/26040/Catal.Today-Weckhuysen-2003.pdf?sequence=1

Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

Supported vanadium oxide catalysts, containing surface vanadia species on oxide supports, are extensively employed as catalysts for many hydrocarbon oxidation reactions. This paper discusses the current fundamental information available about the structure and reactivity of surface vanadia species on oxide supports: monolayer surface coverage, stability of the surface vanadia monolayer, oxidation state of the surface vanadia species, molecular structures of the surface vanadia species (as a function of environment and catalyst composition), acidity of the surface vanadia species and reactivity of the surface vanadia species. Comparison of the molecular structure and reactivity information provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions: (1) the role of terminal VO, bridging VOV and bridging VO-support bonds, (2) the number of surface vanadia sites required, (3) the influence of metal oxide additives, (4) the influence of surface acidic and basic sites, (5) the influence of preparation methods and (6) the influence of the specific oxide support phase. The unique physical and chemical characteristics of supported vanadia catalysts, compared to other supported metal oxide catalysts, for hydrocarbon oxidation reactions are also discussed.

/pdf/structure-and-reactivity-of-surface-vanadium-oxide-species-2t480mfj4r.pdf

Structure and reactivity of surface vanadium oxide species on oxide supports

This paper summarizes the main data appeared in the last years on the oxidative dehydrogenation (ODH) of short chain alkanes on supported vanadium oxide catalysts. The acid-base character of metal oxide support influences the dispersion of vanadium on the surface of the support, as well as the nature of the vanadium species. The reducibility and structure of surface vanadium oxide species and the acid-base character of catalysts, in addition to their catalytic properties in the ODH of C2–C4 alkanes, strongly depend on the metal oxide used as support and the vanadium loading. In this way, it appears that tetrahedral V5+-species are active and selective sites in the ODH of C2–C4 alkanes. The effect of the coordination number and aggregation state of surface vanadium oxide species, and the presence of acid/base sites on the catalytic behavior of supported vanadium oxide catalysts are discussed. It is concluded that these are important factors that must be considered to develop selective catalysts in ODH reactions.

Oxidative dyhydrogenation of short chain alkanes on supported vanadium oxide catalysts

Vanadium oxide monolayer catalysts Preparation, characterization and catalytic activity

Vanadium(V) oxide supported on 7-A1203, GO2, Cr2O3, Si02, Ti02, and Zr02 was studied by X-ray fluorescence, by X-ray diffraction, and especially by the combination of Raman spectroscopy and temperature-programmed reduction (TPR) for qualitative and quantitative structural analysis, respectively. Catalysts were prepared via ion-exchange and wet-impregnation methods. The V contents ranged from - 1 to 40 wt % V. At low surface concentrations only surface vanadate phases of two-dimensional character are observed for all carriers. According to Raman and TPR data the structure of these surface vanadate species is independent of the preparation technique. At medium and high surface concentrations, the webimpregnated samples already contain crystalline V20b At equal surface concentrations the ion-exchanged catalysts contain no V205 crystallites. An exception is Si02 on which also crystalline V206 is formed in both preparation techniques. Monolayer stability toward thermal treatment decreases in the order AZO>3 Ti02> Ce02,w hereas on heating ion-exchanged V/Si02 the crystalline V206 spreads out over the silica surface. The reducibilities of the ion-exchanged catalyats, as measured by TPR, can be used as a measure for the contact interaction between vanadia and the carrier oxides. At temperatures of 500-800 K, this interaction ranges from strong with titania to weak with silica as a carrier.

/pdf/vanadium-oxide-monolayer-catalysts-3-a-raman-spectroscopic-1n1xryax5x.pdf

Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Small amounts of gallium ions were added to y-alumina and their influence on the structural properties of the system Co-(Mo)/y-Al203 was studied. It is shown that, due to the presence of Ga3+ ions, a "surface" spinel CoAl204 is formed with a larger amount of Co2+ in tetrahedral sites as compared to the spinel formed on gallium-free alumina. A decrease of the segregated Co304 is also observed. A possible effect of gallium ions on molybdenum is discussed. It is also reported that different preparation methods (single or double impregnation) lead to the formation of different surface species. Cobalt aluminate, molybdate monolayer, and Co3O4, depending on the Co content, are formed on doubly impregnated specimens. Cobalt aluminate and cobalt molybdate are the main species formed on singly impregnated specimens. Finally brief consideration is given to how the Co and Mo species, present in the oxide form, change in the sulfided form.

/pdf/effect-of-gallium-ions-and-of-preparation-methods-on-the-24vr97toz6.pdf

Effect of gallium ions and of preparation methods on the structural properties of cobalt-molybdenum-alumina catalysts

Vanadium oxide monolayer catalysts. 3. a raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

de Vhj Vincent Beer

Papers

Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Effect of gallium ions and of preparation methods on the structural properties of cobalt-molybdenum-alumina catalysts

Vanadium oxide monolayer catalysts. 3. a raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Effect of Gallium Ions and of Preparation Methods on the Structural Properties of Cobalt-Molybdenum-Alumina Catalysts