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

http://www1.udel.edu/chem/polenova/PDF/Polyoxometalates/POMs_Catalysis_NMR_ChemRev1998.pdf

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

https://web.iitd.ac.in/~arunku/files/CEL311_Y13/Adsorption%20Theory%20to%20practice_Dabrowski.pdf

Adsorption — from theory to practice

ion from a primary OH group of glyc-erol. 223,231 A similar mechanism was proposed manyyears ago for alcohol oxidation on Pt/C, involving asecond step, the transfer of a hydride ion to the Ptsurface (Scheme 11). 8,87,237 We consider it more feasible that the rate-deter-mining step is the cleavage of the C-H bond at theR-carbon atom. A similar mechanism is now generallyaccepted for Au electrodes (Scheme 12). 238 Despite thestructural differences between Au nanoparticles andan extended Au electrode surface, there are alsosimilarities, such as the critical role of aqueousalkaline medium and the absence of deactivation dueto decomposition products (CO and C x H y frag-ments). 239,240 An important question is the nature of active siteson Au nanoparticles. Electrooxidation of ethanol onAu nanoparticles supported on glassy carbon re-quired the partial coverage of Au surface by oxides. 241 Another analogy might be the model proposed for COoxidation. 219,242,243 According to this suggestion, theactive site consists of an ensemble of metallic Auatoms and a cationic Au

Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NO−, NO, (NO)2, N2O3, NO+, NO2 − (different nitro and nitrito anions), NO2, N2O4, N2O5, NO2, and NO3 − (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N2, H-, and C-containing nitrogen oxo species, C─N species, NH x species) are also briefly discussed. Some guidelines for spectral identification of N x O y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded.

Identification of Neutral and Charged N x O y Surface Species by IR Spectroscopy

Calcium–Lead Hydroxyapatites: Thermal and Structural Properties and the Oxidation of Methane

A comparative catalytic study of stoichiometric metal phosphates

Nitrogen dioxide is sorbed by the solid heteropoly acids, the first sorbates producing HNO3 while those subsequently taken up remain strongly bound on the acid, up to three NO2 per heteropoly anion. The sorption of NO2 is shown to be dependent on the elemental composition of the anions of the solid acids and hence on the acid strengths of these materials. The sorbed NO2 associates with both the surface and bulk protons to form HNO2+ thus demonstrating that NO2 is capable of penetrating into the crystallographic structure of the solid acid. Prior sorption of NO2 facilitates the takeup of NO which forms N2O3. 12-tungstophosphoric acid (HPW) supported on silica produces quantitatively different but qualitatively similar results. The microporous ammonium salt of HPW produces markedly different results when exposed to NO2 with the predominant product being N2 evidently resulting from the ammonium cation functioning as a source of the reductant ammonia.

The interaction of nitrogen oxides with metal-oxygen cluster compounds (heteropoly oxometalates)

Temperature programmed desorption experiments have been performed on boron phosphate of eight different phosphorus/boron ( P B ) compositions from 0.89 to 1.40. Four consistently recurring peaks were found, each due to desorbed water, and the variations of the peak intensities and desorption activation energies with P B ratio were examined. This information, together with infrared spectroscopic data obtained earlier, was employed to provide tentative assignments of the surface species involved.

Temperature programmed desorption studies on boron phosphate

The oxidative coupling of methane has been tested over alkali- and alkaline earth-phosphate catalysts at 700 and 775 °C with and without the introduction of a small quantity of tetrachloromethane (TCM) to the feedstream. In general, the conversion of methane was enhanced by the addition of TCM but the effect on selectivity was dependent on the catalyst being examined. The selectivity to C2 and higher hydrocarbons and that to oxidation products have been shown to have a dependence on the cation radius/charge ratio.

John B. Moffat

Papers

Calcium–Lead Hydroxyapatites: Thermal and Structural Properties and the Oxidation of Methane

A comparative catalytic study of stoichiometric metal phosphates

The interaction of nitrogen oxides with metal-oxygen cluster compounds (heteropoly oxometalates)

Temperature programmed desorption studies on boron phosphate

The oxidative coupling of methane on alkali- and alkaline earth-phosphate catalysts