Metal oxide catalysts, role chemicals

It is seen that metal and metal oxide catalysts have significant roles in the catalyHc process for the production of fuels and chemicals. There are several catalysts that are used commercially in the biorefinery system to produce fuels and chemicals. Metal oxides are composed of cations possessing Lewis acid sites and anions wifh Br0nsted base sites. They are classified into single metal oxides and mixed metal oxides. Transition metal oxides have catalytic activity for cellulose hydrolysis, and when used as solid acid catalysts, they are reusable and thus may be easily separated from the reaction mixture. 

Metal complexes, especially involving transition metals, are known for their role as catalysts in a broad variety of chemical processes including isomerization, oxidization, hydrogenation, and polymerization. Such catalytic reactions play an important role not only in many industrial processes, such as petroleum and polymer industries, but also in many biological systems, e.g., a variety of selective oxidation catalysts with heme (1) and nonheme (2) iron centers. The transition metals in these systems usually constitute a fundamental part of the catalyst, due to their... 

This is an important industrial reaction, alone or in combination with others. The CH3OH production is often coupled to oxidation to formaldehyde, methanol to gasoline (Mobil) process, methanol to olefins process, carbonylation, etc. Due to this, a large volume of information already exists on catalyst preparation, kinetics, reactors and all other aspects of the related chemical technology [53]. However, let us concentrate our attention here on just one selected problem the role of the promoter and the nature of the active site on the metal on oxides catalysts. Let us mention in passing that pure metals (promoter free) most likely do not catalyze the synthesis. 

Stoichiometric and catalytic transition-metal oxidation reactions are of great interest, because of their important role in industrial and synthetic processes. The oxidation of alkenes is one of the fundamental reactions in chemistry.1 Most bulk organic products contain functional groups, which are produced in the chemical industry by direct oxidation of the hydrocarbon feedstock. Usually these reactions employ catalysts to improve the yields, to reduce the necessary activation energy and render the reaction more economic. The synthesis of almost every product in chemical industry nowadays employs at least one catalytic step. The oxidation products of alkenes, epoxides and glycols, may be transformed into a variety of functional groups and therefore the selective and catalytic oxidation of alkenes is an industrially important process. 

This review analyzes the properties which are necessary for heterogeneous catalysts to promote the oxyfunctionalization of light paraffins to valuable chemicals. Three catalytic systems are discussed i) vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation of n-butane to maleic anhydride, which is here also examined for reactions aimed at the transformation of other hydrocarbons ii) Keggin-type heteropolycompounds, which are claimed for the oxidation of propane and isobutane, whose composition can be tuned in order to direct the reaction either to the formation of olefins or to the formation of oxygenated compounds iii) rutile-based mixed oxides, where rutile can act as the matrix for hosting transition metal ions or favour the dispersion of other metal oxides, thus promoting the different role of the various elements in the formation of acrylonitrile from propane. 

Recently, oxidative coupling of methane has been studied in order to utilize natural gas as a chemical carbon source. Various materials (ref. 1-12) have been reported to be effective catalysts. However, roles of the catalysts have not been studied well. Ito, Lunsford et al. have reported that an active catalyst has a radical center (for example (Li 0 J) under the reaction condition (ref. 3-a, b, c). Although this must be an essential factor, it seems difficult to explain the effectiveness of such a variety of catalyst materials by one factor. In this study we tried to abstract the important factors to determine the apparent activity and selectivity of this reaction by using MgO catalysts doped with various metal oxides. 

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