Catalytic Reactions with Green Oxidants

Unfortunately, the surface area and porosity of perovskites are insignificant compared to many of the mesoporous oxides. Because of this, an advanced interaction of reactants with the active sites of the catalysts is limited. To overcome this, various attempts were made to synthesize perovskite oxides with high surface areas using different methods such as the decomposition of metal complexes, the sol-gel, or the surfactant-assisted sol-gel and polymerized complex methods. 

In an effort to develop a suitable perovskite catalyst for the oxidation of alky-laromatics to carbonyl compounds, the attention has been focused on the use of LaMOs perovskites. Thus, several ABOg-type perovskite oxides (A = La, Y, Nd, or Gd B = Fe, Mn, Cr, or Co) have been investigated as catalysts for the oxidation of 1,2-dichlorobenzene, a model compound for the highly toxic polychlorinated dibenzodioxins [39]. LaMOg (M = Cr, Co, Fe, Mn, Ni) perovskites were used as catalysts in the oxidation of alkylaromatics to benzylic ketones, under solvent-free conditions, using TBHP as oxidant [48]. LaCrOs was found to be an efficient catalyst for the oxidation of alkylarenes to phenyl ketones, under mild reaction conditions, in the presence of TBHP as oxidant. Perovskites 

The main products were / -toluic acid, 4- carboxybenzaldehyde, and the desired product, the terephthalic acid. 

The hypo-stoichiometric perovskites are able to accommodate a wide variety of oxygen stoichiometries and, therefore, different oxidation states. For Co and Mn, this favors the charge transfer in the oxidation reaction. 

Perovskites with the general elemental composition of ABO3, where B is Fe, also attracted the attention because of their application as catalysts in liquid-phase oxidation reactions. They revealed high catalytic activities in heterogeneous Fenton-like oxidation at neutral conditions [46,47,55,56]. BiFeOs and 

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In fact, the earliest application of kinetic methods was to determine trace levels of substances exerting catalytic activity in oxidation-reduction reactions involving multiple electron transfers (1885-trace level V on its catalysis of the oxidation of aniline). For example, the reduced form of many triphenylmethane dyes is colorless , and loses two electrons on oxidation to the dye. The rate of reaction with such oxidants as 104 is relatively slow, but can be catalyzed by trace levels of transition metal ions which involve single electron transfer in their own redox steps. Thus, trace levels of manganese can be determined by the proportionality of the rate of oxidation of leuco-malachite green by iodate at less than micromolar concentrations. Similarly, trace levels of Cu ", < 10 M, can be determined from the catalytic effect on the atmospheric oxidation of ascorbic acid. Such systems can be written as a generalized redox reaction... 

Abstract The catalytic oxidation is an area of the key technologies for converting petroleum-based feedstocks to useful chemicals such as diols, epoxides, alcohols, and carbonyl compounds. Many efficient homogeneous and heterogeneous oxidation systems based on polyoxometalates (POMs) with green oxidants such as H2O2 and O2 have been developed. This chapter summarizes the remarkable oxidation catalyses by POMs with multimetallic active sites. The multifunctionality of multimetallic active sites in POMs such as cooperative activation of oxidants, simultaneous activation of oxidants and substrates, stabilization of reaction intermediates, and multielectron transfer leads to their remarkable activities and selec-tivities in comparison with the conventional monometallic complexes. Finally, the future opportunities for the development of shape- and stereoselective oxidation by POM-based catalysts are described. 

The multi-component systems developed quite recently have allowed the efficient metal-catalyzed stereoselective reactions with synthetic potential [75-77]. Multi-components including a catalyst, a co-reductant, and additives cooperate with each other to construct the catalytic systems for efficient reduction. It is essential that the active catalyst is effectively regenerated by redox interaction with the co-reductant. The selection of the co-reductant is important. The oxidized form of the co-reductant should not interfere with, but assist the reduction reaction or at least, be tolerant under the conditions. Additives, which are considered to contribute to the redox cycle directly, possibly facilitate the electron transfer and liberate the catalyst from the reaction adduct. Co-reductants like Al, Zn, and Mg are used in the catalytic reactions, but from the viewpoint of green chemistry, an electron source should be environmentally harmonious, such as H2. 

When titanium oxides are irradiated with UV light that is greater than the band-gap energy of the catalyst (about X < 380 nm), electrons (e ) and holes (h+) are produced in the conduction and valence bands, respectively. These electrons and holes have a high reductive potential and oxidative potential, respectively, which, together, cause catalytic reactions on the surfaces namely photocatalytic reactions are induced. Because of its similarity with the mechanism observed with photosynthesis in green plants, photocatalysis may also be referred to as artificial photosynthesis [1-4]. As will be introduced in a later section, there are no limits to the possibilities and applications of titanium oxide photocatalysts as environmentally harmonious catalysts and/or sustainable green chemical systems. ... 

The first part of this chapter is intended to survey recent literature on new catalytic materials because the development of new types of metal oxides and layered- and carbon-based materials with different morphologies opens up novel acid-base catalysis that enables new type of clean reaction technologies. Mechanistic considerations of acid- and base-catalyzed reactions should result in new clean catalytic processes for Green and Sustainable Chemistry, for example, transformations of biorenewable feedstock into value-added chemicals and fuels [21-35]. The latter part of this chapter, therefore, focuses on biomass conversion using solid acid and base catalysts, which covers recent developments on acid-base, one-pot reaction systems for carbon-carbon bond formations, and biomass conversion including synthesis of furfurals from sugars, biodiesel production, and glycerol utilization. 

Method (a) uses nitric acid for the oxidation of the mixture of cyclohexanol/cyclohexanon available by the hydrogenation of phenol process (b) is based on hydroxycarbonylation of 1,3-butadien and process (c) on a catalytic green chemistry reaction with water as the only side product. In this process, cyclohexene is oxidized hy hydrogen peroxide in the presence of tungsten-hased catalyst under phase-transfer catalysis (PTC). 

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