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

(C1−C4) by Heteropoly Compounds Miao Sun,*,† Jizhe Zhang,‡ Piotr Putaj, Valerie Caps, Fred́eŕic Lefebvre, Jeremie Pelletier, and Jean-Marie Basset* †Research and Development Center, Saudi Aramco Oil Company, Dhahran 31311, Saudi Arabia ‡Division of Chemical and Life Sciences and Engineering, and KAUST Catalysis Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Laboratoire de Chimie Organomet́allique de Surface, CPE Lyon, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne, France

Catalytic oxidation of light alkanes (C1-C4) by heteropoly compounds.

Metal oxides have been extensively applied as heterogeneous catalysts in various chemical processes, including conventional heterogeneous catalysis, photocatalysis, and membrane catalysis. The catalytic performance of an oxide heterogeneous catalyst can be affected by its lattice structure, electronic structure, surface properties, bulk defects, and metal–oxygen bond strength. As a catalytic membrane, the catalytic performance of an oxide may also strongly depend on its oxygen-ion diffusion properties. Cation doping has been extensively adopted to tailor, both physically and chemically, the properties of oxide materials, such as lattice structure, electronic structure, lattice defects and diffusion behavior, so as to alter their catalytic performance for various redox reactions. Very recently, anion doping into the oxygen site has emerged as a new strategy for tuning the chemical and physical properties of metal oxides, and thus for regulating their catalytic behavior. Here, a timely review of recent progress in the development of advanced oxide catalysts based on oxygen-site anion doping is provided. Emphasis is given to the effect of doping anions into the metal oxide lattice on the physical and chemical properties, and consequently the performance in various catalytic applications, including the oxidative dehydrogenation of ethane (ODE), oxidative coupling of methane (OCM), photocatalytic reduction of dyes, and ceramic membrane-based oxygen separation. The aim of the current review is to offer some insightful perspectives to guide the development of functional oxide materials based on the anion site doping strategy toward application in heterogeneous catalysis. The knowledge gained here may also be useful for other application fields, such as electrochemical energy storage devices and sensors.

Recent advances in anion-doped metal oxides for catalytic applications

Lower alkanes dehydrogenation: Strategies and reaction routes to corresponding alkenes

Catalytic selective oxidation of propane

Catalysts based on rare earth complexes such as CeO2/2CeF3, Sm2O3/4CeF3, Nd2O3/ 4CeF3 and Y2O3/4CeF3 were prepared. These catalysts were active for the oxidative dehydrogenation of propane with very high selectivity to propene. At 500°C and 6000 h−1, using CeO2/2CeF3 as the catalyst, the conversion of propane was 41.3%, selectivity to propene reached 81.1%, propene yield was 33.5%. XRD results indicated that F− and O2− were exchanged in the lattices. Raman spectra showed that the O
 2
 −
 might be the active oxygen species in propane oxidative dehydrogenation.

Oxidative dehydrogenation of propane over fluorine promoted rare earth-based catalysts

LaF3 modified ZrO2, CeO2 and ThO2 catalysts for the oxidative coupling of methane indicate that ZrO2/LaF3, CeO2/LaF3 and ThO2/LaF3 catalysts have high activity and high selectivity at low temperature. In the temperature region 480–650 °C, the methane conversion is 24.38–30.8% and the C2= selectivity is 40–55.38%. The characterization of oxygen species on the catalysts indicates that, because of the modification of LaF3 to ZrO2, CeO2 and ThO2, it is favourable for the activation of O2.

Methane oxidative coupling over fluoro-oxide catalysts

CeO2/BaF2 was used as the catalyst for the oxidative coupling of methane (OCM). At 800°C and CH4∶O2=2.7∶1,CH4 conversion of 34% with C2 hydrocarbon selectivity of 54.3% was obtained. XRD measurement showed that partial anion (O2−,F−) and/or cation (Ce4+,Ba2+) exchange between CeO2 and BaF2 lattices occurred. ESR study showed that O− species existed on degassed catalyst. XPS study revealed that, when BaF2 was added to CeO2, the binding energy of Be 3d5/2 was 2.2 eV lower than that in CeO2, and the “electron-enriched lattice oxygen” species was detected. XPS, ESR and Raman study showed that, under O2 adsorbing conditions, O22− and O−2 species were detected on CeO2/BaF2.

The oxidative coupling of methane and the activation of molecular o2 on ceo2/baf2

The multi-valence anion modified complex catalyst Y2O3–CeF3 was found to be selective for the oxidative dehydrogenation of isobutane to isobutene at a relatively high conversion.

Weide Zhang

Papers

Oxidative dehydrogenation of propane over fluorine promoted rare earth-based catalysts

Methane oxidative coupling over fluoro-oxide catalysts

The oxidative coupling of methane and the activation of molecular o2 on ceo2/baf2

Selective oxidative dehydrogenation of isobutane over a Y2O3–CeF3 catalyst

Catalyst for producing propene by propane oxidation and dehydrogenation