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

12-tungstophosphoric and 12-molybdophosphoric acids are capable of sorbing and reducing CO2 without the presence of added reductants The adsorbed CO2 (physisorbed as CO2) desorbs from the acids and salts at low temperatures (50–200°C) Carbon dioxide also desorbs only from the acids at high temperatures (500–600°C), suggesting the direct or indirect involvement of the protons in the process and the importance of the Keggin unit as well Raman and DRIFTS results show that the species responsible for the evolution of CO2 (at high temperatures) are carbonaceous in nature Carbon deposits extract the anionic oxygen atoms from the Keggin units during the high-temperature desorption process The extraction of anionic oxygen atoms by carbon is confirmed using labeled carbon dioxide The spectroscopic data imply that carbon exists on the surface as such but, additionally, as either carbon or CO2 bound to the terminal oxygen atoms of the Keggin anion

Adsorption and reduction of CO2 on 12-tungstophosphoric and 12-molybdophosphoric acids in the absence of added reductants

Heteropoly compounds are ionic solids in which not only the cation may be varied but also the composition of the anion, which itself consists of a minimum of two metallic elements. This provides for changes in the functionality of the catalyst, from one in which the acidic properties are prevalent, to one with activity in oxidation processes. The former are shown to be related to the magnitude of negative charges on the terminal or outer oxygen atoms, while the latter depends on the binding energies of these same oxygen toms to the peripheral metal atoms of the anion.

A Controlled Catalytic Environment: Heteropoly Compounds

Work in this laboratory has now shown that certain of the salts of the heteropoly oxometalates of Keggin structure with monovalent cations can be prepared with microporous structure. These represent a new class of microporous solids. Data for the adsorption-desorption of nitrogen together with information from X-ray diffraction studies have been analyzed to provide a rationalization of the results.

Microporosity in Heteropoly Oxometalate Catalysts

Quantitative Determination of Formic Acid and its Decomposition Products by GC

Various zirconia were prepared from ZrOCl2·8H2O by the addition of aqueous ammonia and potassium hydroxide; the effect of the catalyst preparation on the oxidative coupling of methane over zirconia was studied. The selectivity to such C2 compounds as ethylene and ethane was strongly influenced by the pH of the preparative solution of ZrOCl2·8H2O, NH3 aq, and KOH, as well as the sequence of the addition of each hydroxide during the preparation of the catalyst.

John B. Moffat

Papers

Adsorption and reduction of CO2 on 12-tungstophosphoric and 12-molybdophosphoric acids in the absence of added reductants

A Controlled Catalytic Environment: Heteropoly Compounds

Microporosity in Heteropoly Oxometalate Catalysts

Quantitative Determination of Formic Acid and its Decomposition Products by GC

Effect of Potassium-Treated Zirconia on the Oxidative Coupling of Methane