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

Activation and regeneration procedures applied to a nickel-molybdenum on alumina catalyst, both fresh and spent, were tested by the hydrodesulfurization of thiophene. Characterization techniques used included temperature programmed reduction and oxidation (TPR, TPO), diffuse reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The fresh catalyst was treated by sulfiding, reoxidation, and resulfiding. This sequence was found to be more effective than one sulfiding step, possibly because of the formation of a nickel molybdate phase during reoxidation. The spent catalyst could not be regenerated completely although its original surface properties were attained. The loss of activity of the spent catalysts was alluded by TPO to result from nickel-molybdenum segregation which probably happened because of the excessive heat from burning the coke present on the catalyst

Activation and Regeneration of a NiMo/Al2O3 Hydrotreatment Catalyst

Partial oxidation of methane and reforming of methane with CO2 were carried out with Pt/Al2O3, PtZrO2 and Pt/CeO2 catalysts, in the temperature range of 350–900 °C. For partial oxidation, the catalysts showed similar stabilities, with the PtZr slightly more active. The reaction occurs in two simultaneous stages: total combustion of methane and reforming of the unconverted methane with steam and CO2, with the O2 conversion of 100% over the whole temperature range. For reforming with CO2, the catalysts presented similar activities, but with distinct deactivation rates: while the PtAl deactivates very fast at 800 °C, due to deposition of inactive carbon, the PtZr and PtCe catalysts offer higher resistance to coke formation, due to the metal-support interactions and the higher mobility of oxygen in the oxide lattice.

Martin Schmal

Papers

Activation and Regeneration of a NiMo/Al2O3 Hydrotreatment Catalyst

Methane conversion to synthesis gas by partial oxidation and CO2 reforming over supported platinum catalysts

Influence of acid sites on the hydrodeoxygenation of anisole with metal supported on SBA-15 and SAPO-11

Ligand and Geometric Effects on Pt/Nb2O5and Pt–Sn/Nb2O5Catalysts☆

A study of the promoting effect of noble metal addition on niobia and niobia alumina catalysts