Catalysts metal oxidation

Figure 1 is a TEM photograph of the Cu (10wt%)/Al2O3 catalyst prepared by water-alcohol method, showing the dispersed state of copper and was confirmed the particle sizes from XRD data. Figure 2 is X-ray diffraction patterns of above-mention catalysts, was used to obtain information about phases and the particle size of prepared catalysts. Metal oxide is the active species in this reaction. Particle sizes were determined fix)m the width of the XRD peaks by the Debye-Scherrer equation. 

The present model deals with a supported transition metal cation which is highly dispersed, at the molecular scale, on an oxide, or exchanged in a zeolite. In the case of zeolite-supported cations, the formation of different metal species in metal/zeolite catalysts (metal oxides, metal oxocations, besides cationic species) has been considered by different authors who have suggested these species to play key roles in SCR catalysis [14,15], This supported cation can also be considered as located at a metal oxide/support interface. 

In this chapter, we have discussed the application of metal oxides as catalysts. Metal oxides display a wide range of properties, from metallic to semiconductor to insulator. Because of the compositional variability and more localized electronic structures than metals, the presence of defects (such as comers, kinks, steps, and coordinatively unsaturated sites) play a very important role in oxide surface chemistry and hence in catalysis. As described, the catalytic reactions also depend on the surface crystallographic structure. The catalytic properties of the oxide surfaces can be explained in terms of Lewis acidity and basicity. The electronegative oxygen atoms accumulate electrons and act as Lewis bases while the metal cations act as Lewis acids. The important applications of metal oxides as catalysts are in processes such as selective oxidation, hydrogenation, oxidative dehydrogenation, and dehydrochlorination and destructive adsorption of chlorocarbons. 

The selective oxidation of propene to acetone can be effected by two entirely different types of catalysts metal oxide combinations, which contain Mo03 as the essential component, and catalysts based on palladium. 

As discussed in a previous section, metal oxides represent an important class of materials exhibiting a broad range of properties from insulators to semiconductors and conductors and have found applications as diverse as electronics, cosmetics and catalysts. Metal oxides have been widely used in many valuable heterogeneous catalytic reactions. Typical metal oxide-catalyzed reactions, including alkane oxidation, biodiesel production, methanol adsorption and decomposition, destructive adsorption of chlorocarbons and warfare agents, olefin metathesis and the Claisen-Schmidt condensation will be briefly discussed as examples of metal oxide-catalyzed reactions. 

While the specific surface area of carriers is often determined—as we have seen above—by using physical adsorption, the active phase of the catalysts (metal, oxide, sulphur) can be studied by selective chemisorption (with no support interaction) of an adsorbate under conditions of pressure and temperature permitting the formation of a single layer on the surface of the metal. During chemical adsorption, there is a chemical reaction between the gas molecule and the active phase, which is represented by the transfer or sharing of electrons. 

Thus oxygen is chemisorbed on all simple semiconducting catalysts— metal oxides—and in a number of cases it is partly dissolved in the lattice. 

The catalytic partial oxidation (CPO) of methane is an interesting alternative to to the well-established steam reforming (SRM) process for syngas production in small-scale units. However, due to the severe reaction conditions (T = 800-950°C, contact times of few ms) in CPO processes, stable and active catalysts are still required. Several catalytie systems have been used in this process, such as noble metal-based catalysts, metal-based catalysts, metal oxide catalysts and perovskites [1]. In particular, catalysts obtained by the calcination of hydrotalcite-like compounds (HTlcs) have been widely used in the CPO of methane, as they can be easily and cheaply synthesized, with a highly-dispersed... 

Keywords Anodization Catalysts Metal oxide semiconductors Photoelectrochemical hydrogen production... 

Additionally, several reports of homogeneous water-oxidation catalysts pointed to the possibility that the complexes are not the catalysts and are acting as precursors to the respective metal oxides, which are ultimately the actual water-oxidation catalysts. Metal oxides have been known to catalyse water oxidation, but the most active were often oxides of rare- and precious-metal ions, operating best in highly basic conditions. " The past decade has seen major advances in the development of highly active metal-oxide catalysts based on cost-effective, abundant and nontoxic elements that can act under near-neutral pH conditions. These metal oxides can... 

Properties Free-radical polymerization Ziegler-Natta type catalysts Metal oxides on support... 

For technical purposes, a melt pol5nnerization method is used, the dicarboxyHc acid component being acids or esters (37). As catalysts metal oxides or acetate salts may be used, such as manganese(ll) acetate tetrahydrate and antimony(III) trioxide. 

Pt-based catalysts are two necessary approaches at the current technology stage. It is believed that non-noble metal electrocatalysts is probably the sustainable solution for PEM fuel cell commercialization. In the past several decades, various nonnoble metal catalysts for ORR have been explored, including non-pyrolyzed and pyrolyzed transition metal nitrogen-containing complexes, transition metal chalcogenides, conductive polymer-based catalysts, metal oxides/carbides/nitrides/ oxynitrides/carbonitrides, and enzymatic compoimds. The major effort in non-noble metal electrocatalysts for ORR is to increase both the catalytic activity and stability. 

Most importantly, the propensity for chemical reaaion between water and cleaning solvent (and soils) inaeases when there are metal oxides present which can be catalysts. Metal oxides can play another reartionary role — they can be the reactant with water instead of the catalyst for its reaction with water. 

Single-Metal Catalysts Metal oxides such as Ce02 [17, 46], Zr02 [47], and Ti02 [48]which are non-soluble in the reaction medium (heterogeneous) have been used... 

Based on their experimental studies, the authors of [55] concluded that the catal)4ic process is more efficient. However, even the best result they reported (a total selectivity of formation of oxygenates of 57% at a conversion of 2% on an Ag20/Cr2Q3 catalyst at P = 50 atm) does not exceed the corresponding values for the gas-phase reaction. Of course, catalysts substantially, by 100—125 °C, reduce the temperature of the process [56], which produces a positive effect, at least, by preventing a further conversion of the oxygenates formed. Note, however, that, while in the majority of the experiments in the gas phase, no formation of CO2 was detected [148], the CO2 yield in the presence of a catalyst (metal oxides) even exceeded that of CO, indicative of a key role of the catalyst in the formation of deep-oxidation products. 

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