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

Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.

Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis

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

Pt–xMo/γ-Al2O3 catalysts of different molybdenum loading (2–20 wt.%) and with 1 wt.% of platinum were prepared by successive wet impregnation after intermediate calcination. The structure, morphology and surface were characterized by various methods. The DRS results indicate the presence of octahedral Mo6+ and tetrahedral Mo6+ phases. It also evidences the presence of polymeric MoOx species, responsible for the formation of a well dispersed surface sublayer and bulk MoO3 crystalline phase. XPS results after reduction and passivation of the 1Pt and 1Pt2Mo revealed the presence of residual chlorine, in the form of surface species such as [Pt(OH)xCly]s and [PtOxCly]sfavoring the formation of well dispersed platinum particles. The TPD and FTIR results are consistent with the existence of new active sites of Pt in the presence of molybdenum loading. For low Mo content there is a H2 spillover effect. These results confirm the decoration model of Pt encapsulation by partially reduced Mo species as well as H2 storage and backspillover due to the generation of a bronze compound.

Interaction between Pt and MoO3 dispersed over alumina

Pt–TiO2–γ Al2O3Catalyst*1I. Dispersion of Platinum on Alumina-Grafted Titanium Oxide

The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO 3 /Al 2 O 3 catalyst than on the Pd/CeO 2 /Al 2 O 3 and Pd/Nb 2 O 5 /Al 2 O 3 catalysts. The explanation for the very high N 2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me δ + stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N 2 selectivity.

Martin Schmal

Papers

Interaction between Pt and MoO3 dispersed over alumina

Pt–TiO2–γ Al2O3Catalyst*1I. Dispersion of Platinum on Alumina-Grafted Titanium Oxide

The nature of metal oxide on adsorptive and catalytic properties of Pd/MeOx/Al2O3 catalysts

Carbon Monoxide Hydrogenation on Co–Rh/Nb2O5 Catalysts

Activity and selectivity of Pt-Sn/Nb2O5 in n-heptane conversion