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.

A study is conducted to demonstrate catalytic dehydrogenation of light alkanes on metals and metal oxides. The study provides a complete overview of the materials used to catalyze this reaction, as dehydrogenation for the production of light olefins has become extremely relevant. Relevant factors, such as the specific nature of the active sites, as well as the effect of support, promoters, and reaction feed on catalyst performance and lifetime, are discussed for each catalytic Material. The study compares different catalysts in terms of the reaction mechanism and deactivation pathways and catalytic performance. The duration of the dehydrogenation step depends on the heat content of the catalyst bed, which decreases rapidly due to the endothermic nature of the reaction. Part of the heat required for the reaction is introduced to the reactors by preheating the reaction feed, additional heat being provided by adjacent reactors that are regenerating the coked catalysts.

Catalytic dehydrogenation of light alkanes on metals and metal oxides.

Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided. Presented are both theoretical and experimental evidence pointing to inherent differences in the reaction mechanism over transition metals. These differences are related to methane dissociation, binding site preferences, the stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species. Methane dissociation requires a reduced metal surface, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H, H2, C or CO. The comparison of elementary reaction steps on Pt and Rh illustrates that a key factor to produce hydrogen as a primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H2 and CO as primary products is a low surface coverage of intermediates, such that the probability of O–H, OH–H and CO–O interactions are reduced. The local concentrations of reactants and products change rapidly through the catalyst bed. This influences the reaction mechanisms, but the product composition is typically close to equilibrated at the bed exit temperature.

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts

Selective catalytic hydrogenation has wide applications in both petrochemical and fine chemical industries, however, it remains challenging when two or multiple functional groups coexist in the substrate. To tackle this challenge, the "active site isolation" strategy has been proved effective, and various approaches to the site isolation have been developed. In this review, we have summarized these approaches, including adsorption/grafting of N/S-containing organic molecules on the metal surface, partial covering of active metal surface by metal oxides either via doping or through strong metal-support interaction, confinement of active metal nanoparticles in micro- or mesopores of the supports, formation of bimetallic alloys or intermetallics or core@shell structures with a relatively inert metal (IB and IIB) or nonmetal element (B, C, S, etc.), and construction of single-atom catalysts on reducible oxides or inert metals. Both advantages and disadvantages of each approach toward the site isolation have been discussed for three types of chemoselective hydrogenation reactions, including alkynes/dienes to monoenes, α,β-unsaturated aldehydes/ketones to the unsaturated alcohols, and substituted nitroarenes to the corresponding anilines. The key factors affecting the catalytic activity/selectivity, in particular, the geometric and electronic structure of the active sites, are discussed with the aim to extract fundamental principles for the development of efficient and selective catalysts in hydrogenation as well as other transformations.

Selective Hydrogenation over Supported Metal Catalysts: From Nanoparticles to Single Atoms

The liquid-phase hydrogenation of citral was studied at 393 K and 10 bar on Pt–Co/C catalysts, having different Pt/(Pt + Co) ratios and containing a total metal load of about 2%. The monometallic and bimetallic Pt–Co/C catalysts were prepared by impregnation and co-impregnation, respectively, with cobalt tris(acetylacetonate) and platinum bis(acetylacetonate). Monometallic Pt/C and Co/C catalysts showed very low activity and selectivity to the desired products. Undesirable reactions, such as citral decarbonylation and hydrogenolysis, were observed with these monometallic catalysts. Instead, bimetallic Pt–Co/C proved very active and selective to geraniol/nerol and the main products detected were geraniol/nerol, citronellal and citronellol. Hydrogenation kinetic constants were determined by modeling catalytic data and using a pseudo-homogeneous kinetics. From the analysis of the kinetic parameters, an optimum Pt/(Pt + Co) ratio was found for both the catalytic activity and selectivity towards geraniol/nerol. Furthermore, it was determined that this optimum ratio depends on the activation conditions. Temperature-programmed reduction (TPR) experiments and X-ray absorption spectroscopy (XAS) demonstrated the existence of Pt–Co bimetallic compounds on the carbon support. On the basis of these results, it was proposed that cobalt improves the catalytic performance of platinum by electron transfer. This electron transfer is favored by the high interaction of both metals existing in these types of bimetallic compounds.

Selective liquid-phase hydrogenation of citral over supported bimetallic Pt–Co catalysts

A study of the texture and structure of Raney nickel

The behaviour of Ni supported catalysts, obtained using Ni(NO3)2 and Ni-acetylacetonate as precursor compounds, is analyzed It is observed that initial activities and selectivities are similar for both systems, but the stability differs significantly The systems show different carbon structures and sintering rates, depending on the precursor compound employed

Partial oxidation of methane to synthesis gas. Behaviour of different Ni supported catalysts

Sintering of Chlorinated Pt/γ-Al2O3 Catalysts: An In Situ Study by X-Ray Absorption Spectroscopy

Niobium oxide supported Pd−Co catalysts were characterized through XPS (X-ray photoelectron spectroscopy), (XPS), temperature-programmed reduction (TPR), magnetic measurements, X-ray diffraction, and extended X-ray absorption fine structure (EXAFS). XPS analyses suggested the presence of Co3O4 particles and Co2+ surface phase. TPR and magnetic measurements showed that the palladium addition promoted not only the reduction of Co3O4 particles but also the cobalt surface phase. Magnetic measurements and EXAFS analyses revealed the Pd−Co alloy formation during reduction. A model represented by bimetallic particles enriched with palladium and particles containing only cobalt was proposed.

B. Moraweck

Papers

Selective liquid-phase hydrogenation of citral over supported bimetallic Pt–Co catalysts

A study of the texture and structure of Raney nickel

Partial oxidation of methane to synthesis gas. Behaviour of different Ni supported catalysts

Sintering of Chlorinated Pt/γ-Al2O3 Catalysts: An In Situ Study by X-Ray Absorption Spectroscopy

Characterization of Niobia-Supported Palladium−Cobalt Catalysts