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

Influence of Zirconia Preparation on the Selectivity for Oxidative Coupling of Methane

The oxidative coupling of methane has been studied on three salts of lanthanum, the oxide, phosphate, and sulfate, both in the absence and in the presence of carbon tetrachloride (TCM) in the feed stream. The results show that the anion has a significant effect on both the conversion and selectivity to C 2+ hydrocarbons. At 835°C, for example, the C 2+ selectivities and conversions follow the order La 2 (SO 4 ) 3 > La 2 O 3 > LaPO 4 and La 2 O 3 > LaPO 4 > La 2 (SO 4 ) 3 , respectively. The addition of TCM to the feedstream increases the conversion and the selectivity to C 2 H 4 on La 2 (SO 4 ) 3 but decreases the conversion on LaPO 4 and has little influence on these quantities with La 2 O 3

Anion effects in the oxidative coupling of methane on salts of lanthanum

Zirconium oxide is shown to be capable of catalyzing the conversion of methane to ethane at temperatures as low as 530 °C. The lowest temperature at which ethane is produced is found to be dependent upon the method employed for the preparation of the catalyst. The presence of surface hydroxyl groups appears to be necessary for the production of ethane at these low temperatures.

The low-temperature oxidative coupling of methane over zirconium oxide

The oxidation of propane has been investigated in the presence and absence of tetrachloromethane (TCM) on calcium hydroxyapatite (CaHAp), Ca3(PO4)2, CaSO4 and CaO at 723 K. In the absence of TCM, the conversion of C3H8 on CaHAp was 7.7–9.2% during 6 h on-stream while that on Ca3(PO4)2, CaSO4 and CaO was 0.6, 0 and 0.2–0.4%, respectively. The principal products on all catalysts in the absence of TCM were CO and CO2 with small selectivities to C3H6 and C2H4 (both 5–6%) observed on CaHAp. Upon addition of TCM, the selectivity to C3H6 on all catalysts and the conversion of C3H8 on CaSO4 increased while, with increasing time-on-stream, the changes in the conversion and selectivity were dependent upon the nature of the catalysts. XPS and XRD analyses provide evidence for the presence of chlorine in the surface and/or bulk of three of the catalysts, suggesting that chlorinated species on the solids play a role in the selectivity enhancement, but the absence of chlorine from the sulphate demonstrates the dissimilarities of the catalysts in their abilities to sorb and decompose TCM.

Alkene selectivity enhancement in the oxidation of propane on calcium-based catalysts

The magnesium, calcium, strontium and barium salts of 12-tungstophosphoric and 12-molybdophosphoric acids have been prepared. Evidence of the presence of the Keggin anion (primary structure) was obtained from infrared spectroscopic measurements but powder X-ray diffraction and differential thermal analysis measurements indicated that changes to the secondary structure had occurred. BET surface areas were small for all of the materials studied and no dependence on the cation radius was observed. A crystallographic investigation demonstrated that divalent cations were not incorporated into the lattice suggesting that materials believed to be divalent 12-heteropoly salts are mixtures of the parent acid and a divalent cation salt.

John B. Moffat

Papers

Influence of Zirconia Preparation on the Selectivity for Oxidative Coupling of Methane

Anion effects in the oxidative coupling of methane on salts of lanthanum

The low-temperature oxidative coupling of methane over zirconium oxide

Alkene selectivity enhancement in the oxidation of propane on calcium-based catalysts

The interaction of alkaline earth cations with metal-oxygen cluster compounds and the implications for their use as heterogeneous catalysts