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

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels.

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Ultrathin metal films and particles on oxide surfaces: structural, electronic and chemisorptive properties

Successive reduction steps of CeO2 particles by hydrogen between 300 and 1070 K have been followed by temperature-programmed reduction (TPR) and in situ magnetic measurements on several samples with different BET surface areas. The nature of the phases present in cerias reduced between 670 and 1270 K was determined by X-ray analysis. Finally, reoxidation by oxygen or air was studied at room temperature for all the reduced samples.Magnetic and TPR results show a direct relationship between the degree of reduction and the BET surface area. Indeed, for most of the samples, the degree of reduction at 620–670 K determined by magnetism corresponded to the creation of one layer of Ce3+ ions at the surface of the ceria. A similar relationship between the BET surface area and the extent of reduction was established using the area of the low-temperature TPR composite peak, the maximum of which was found to be constant at 810 K.When the reduction progresses further into the bulk, two main phases were evidenced: first, and expanded cubic CeO2 –x phase derived from the initial ceria by a dilatation of the whole structure and, for deeply reduced samples, the hexagonal Ce2O3 phase. A new intermediate phase, cubic Ce2O3, was also observed on samples reduced at 1070–1170 K.Complete reoxidation by oxygen occurs at room temperature, for all reduction percentages below ca. 60 %, i.e. as long as the reduced phase remained in the cubic form. When the hexagonal Ce2O3 phase has been formed, the reoxidation cannot be completed at 294 K.

Roger Fréty

Papers

Reduction of cerias with different textures by hydrogen and their reoxidation by oxygen

Utilization of vegetable oils as an alternative source for diesel-type fuel: hydrocracking on reduced Ni/SiO2 and sulphided Ni-Mo/γ-Al2O3

Platinum-rhenium-alumina catalysts: III. Catalytic properties

Platinum-rhenium-alumina catalysts: II. Study of the metallic phase after reduction

Platinum-rhenium/alumina catalysts: I. Investigation of reduction by hydrogen