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Mixed oxide
About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.
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TL;DR: It is revealed by H2-TPR that the addition of K increases the amount of active Co sites and the mobility of bulk lattice oxygen due to the low melting point of K-containing compounds, the low valence of K+ and the strong interaction between K and Mg(Al).
59 citations
TL;DR: In this paper, Alumina-supported platinum catalysts have been modified with silicon oxide thin films grown using atomic layer deposition (ALD) in order to tune acid base and electronic properties of the oxide, and their performance has been tested for the hydrogenation of cinnamaldehyde.
Abstract: Alumina-supported platinum catalysts have been modified with silicon oxide thin films grown using atomic layer deposition (ALD) in order to tune the acid–base and electronic properties of the oxide, and their performance has been tested for the hydrogenation of cinnamaldehyde. It was found that the silica layers greatly increase the stability of the platinum nanoparticles, preventing their sintering during high-temperature calcinations without affecting access to the metal surface in any significant way; the extent of CO adsorption, measured by infrared absorption spectroscopy was found to decrease by only one-third after 6 SiO2 ALD cycles. Additional Bronsted and Lewis acid sites were created upon the deposition of submonolayer coverages of silicon oxide, as probed via pyridine adsorption. The addition of the silicon oxide thin films reduced the overall activity of these catalysts but also increased their selectivity toward the production of the unsaturated alcohol. In addition, both turnover frequencies...
58 citations
TL;DR: A novel Ti doped Sm-Mn mixed oxide catalyst designed for the selective catalytic reduction (SCR) of NOx with NH3 at low temperature exhibited superior performance, and was conducive to the reasonable design of low temperature NH3-SCR catalysts generated by adjusting fabrication.
Abstract: A novel Ti-doped Sm-Mn mixed oxide (TiSmMnOx) was first designed for the selective catalytic reduction (SCR) of NOx with NH3 at a low temperature. The TiSmMnOx catalyst exhibited a superior catalytic performance, in which NOx conversion higher than 80% and N2 selectivity above 90% could be achieved in a wide-operating temperature window (60-225 °C). Specially, the catalyst also showed high durability against the large space velocity and excellent SO2/H2O resistance. Ti incorporation can efficiently inhibit MnOx crystallization and tune the MnOx phase during calcination at a high temperature. Subsequently, a high specific surface area as well as an increased amount of acid sites on the TiSmMnOx catalysts were produced. Further, the reducibility of the Sm-doped MnOx catalyst was modulated, facilitating NO oxidation and inhibiting NH3 nonselective oxidation. Consequently, a superior SCR activity was achieved at a low temperature and the operating temperature window of the TiSmMnOx catalyst was significantly widened. These findings may provide new insights into the reasonable design and development of the new non-vanadium catalysts with a high NH3-SCR activity for industrial application.
58 citations
TL;DR: It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-CE bridges developed in the parent calcined samples.
Abstract: A series of Fe-Ce mixed oxides (95 atom % Fe-5 atom % Ce) has been prepared by different methods: coprecipitation, impregnation, and physical mixture of Ce and Fe oxides. These solids have been tested in the Fischer-Tropsch synthesis. The characterization of the catalytic precursors was carried out by X-ray diffraction (XRD), Raman, Mossbauer, and X-ray photoelectron (XPS) spectroscopic techniques. When the preparation method ensures a microscopic contact between Fe and Ce cations in the solid, several types of Fe-Ce interactions are present in the calcined solids. The interactions take the shape of Fe-O-Ce bridges that can exist either in the hematite-like solid solution or in the interphase between the Fe oxide covered by microcrystals of Ce oxide. In the case of the hematite-like solid solution, Ce(IV) cations are dissolved in the alpha-Fe2O3 network. The promotion by Ce of the catalytic properties observed in the final catalysts can be directly related with the detection of these Fe-O-Ce bridges in the calcined solids. The Ce promotion results in a larger yield to hydrocarbons, a higher production of olefins, and a higher selectivity to medium and large chain hydrocarbons (larger than six carbon atoms). It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-Ce bridges developed in the parent calcined samples.
58 citations
TL;DR: In this article, the authors review the recent progress in this field and present a review of the literature on the surface properties of clays and clay-like materials, as well as their properties in the natural environment.
Abstract: Clay minerals are important constituents of the earth's crust not only because of their abundance but merely because of their chemical activity. Clays found in soils and in sediments are distributed among three main mineralogical groups: the kaolin, hydrated micas, and smectite groups. Allophanes derived from volcanic glasses and amorphous Al-Si or Fe-Si mixed oxide gels are also abundant in large areas. These clays and clay-like materials share two common characteristics: a high specific surface area and the presence of exposed cations on their surface. In the natural environment these cations are either Na +, K +, Ca2+, or Mg2+, and/or polynucleic Al or Fe basic cations such as [AI(OH-)x(H20)yJ�+ or [Fe(OH-)x(H20)yJ�+. They balance the excess negative charge of the lattice, generated by isomorphic substitutions (for instance substitution of Si4+ by AI3+ in tetrahedral position, or AI3+ by Mg2+ in octahedral position). A clay microcrystal may thus be considered as the salt of a weak acid, whose anion (i.e. the lattice) has an infinite radius of curvature. In this situation the electrical charges of the cations generate a high electrostatic field because of the very incomplete screening of the positive charges by the anionic lattice charges. Since the lattice charges have fixed positions, the electrical neutrality is easily achieved by monovalent alkali cations, while for divalent cations the situation is much less favorable. Oxygen atoms or hydroxyl groups are the main surface constituents. They may play an important role by forming hydrogen bonds with proton donor or acceptor molecules. In addition, van der Waals (or dispersion) forces are expected to be quite active because of the magnitude of the surface area. In the natural environment a variable number of layers of water molecules but also polar organic molecules do form an adsorbed phase in which many kinds of chemical transformations may occur. The surface constituents and the adsorbed water may show a high catalytic activity in these transformations. The aim of this contribution is to review the recent progress of our knowledge in this field. After a paragraph in which the surface properties of clays and clay-like minerals
58 citations