Reaction selective oxidation

Figure 5. Range of Selective Oxidation Reactions Catalyze by the TS-1 Zeolite System Using Aqueous H202 as Oxidizing Agent...

In the present study, we report the synthesis, characterisation and catalytic properties (in selective oxidation reactions) of copper acetate, copper tetradecachlorophthalocyanine and copper tetranitrophthalocyanine encapsulated in molecular sieves Na-X, Na-Y, MCM-22 and VPI-5. Both molecular oxygen and aqueous HjOj have been used as the oxidants. The... 

In the cases of the selective oxidation reactions over metal oxide catalysts the so-called Mars-van Krevelen or redox mechanism [4], involving nucleophilic oxide ions 0 is widely accepted. A possible role of adsorbed electrophilic oxygen (molecularly adsorbed O2 and / or partially reduced oxygen species like C , or 0 ) in complete oxidation has been proposed by Haber (2]. However, Satterfield [1] queried whether surface chemisorbed oxygen plays any role in catalytic oxidation. 

A growing number of research groups are active in the field. The activity of reforming catalysts has been improved and a number of test reactors for fuel partial oxidation, reforming, water-gas shift, and selective oxidation reactions were described however, hardly any commercial micro-channel reformers have been reported. Obviously, the developments are still inhibited by a multitude of technical problems, before coming to commercialization. Concerning reformer developments with small-scale, but not micro-channel-based reformers, the first companies have been formed in the meantime (see, e.g., ) and reformers of large capacity for non-stationary household applications are on the market. 

There is not much to be said about the use of micro reactors for bulk chemicals and commodities. Worz et al. are so far the only ones who have disclosed their work on the potential of micro-structured reactors for the optimization of chemical processes performed on a large scale ofindustrial relevance [110,112,154,288-290]. This included a fast exothermic liquid/liquid two-phase reaction, which was used for the industrial production of a vitamin intermediate product, and a selective oxidation reaction for an intermediate, a substituted formaldehyde derivative. 

Based upon the activity and electrochemical experimental results the 5%Pt,l%Bi/C catalyst was chosen for further detailed evaluation. For the catalyst to be effective in industrial applications it is desirable that it should remain active for a number of reaction cycles. The recycle capability of 5%Pt,l%Bi/C was evaluated under realistic conditions for a number of selective oxidation reactions, see Table 3. 

Neumann and Khenkin28 review most of the various oxidation methods of dienes and polyenes and their mechanisms. They obviously emphasize the difference between non-conjugated and conjugated dienes and polyenes in selected oxidation reactions. 

Au-Pd alloys with compositions close to that of the bulk components and that particle sizes were ca. 25 to 50 nm in diameter. The catalysts that were effective for H2O2 synthesis were found to be wholly inactive for CO oxidation at ambient temperature, and catalysts that were effective for low temperature CO oxidation were inactive for H2O2 synthesis. This shows that selective oxidation reactions active may utilize very different sites than those for the oxidation of CO. 

Silver is especially attractive among all metals. As we all know, the composite silver nanomaterials are used in many application fields, such as photoelectricity science, film separation, catalysis, and so on. Composite silver catalyst is usually applied in selective oxidation reaction. ... 

It is stable for oxygen evolution and very interesting for selective oxidation reactions ([21] see Chapters 6,15), an industrial application is one step of the vitamin C production [22]). 

He got a Habilitation a diriger les recherches in 2008 and he is now developing his own project that consists of the elaboration of new hybrid metalloprotein catalysts for selective oxidation reactions, by insertion of metal cofactors into xylanases. He then studies their peroxidase, catalase, and monooxygenase activities, in particular in the selective oxidation of sulfides, alkanes, and alkenes. 

Elaboration of new hybrid metalloproteins catalysts for selective oxidation reactions. 

Following the discovery of TS-1 [125], a titanium-substituted MFl, the use of zeolitic materials for oxidation increased significantly. The presence of the Ti atom in the framework of a zeolite structure provides a site-isolated Ti center, a situation not possible with other Ti-containing materials while also allowing shape-selective oxidations. The combination of the two effects gives highly active and selective oxidation reactions [126]. 

Bellussi, G. and Rigutto, M.S. (2001) Metal ions associated to molecular sieve frameworks as catalytic sites for selective oxidation reactions. Stud. 

Kinetics There have been few comprehensive studies of the kinetics of selective oxidation reactions (31,32). Kinetic expressions are usually of the power-rate law type and are applicable within limited experimental ranges. Often at high temperature the rate expression is nearly first order in the hydrocarbon reactant, close to zero order in oxygen, and of low positive order in water vapor. Many times a Mars-van Krevelen redox type of mechanism is assumed to operate. 

Mechanisms There is a derth of knowledge about the mechanisms operative in selective oxidation reactions. The only exceptions are the reactions of ethylene to ethylene oxide on supported silver catalysts and of propylene to acrolein on bismuth molybdate type catalysts. For the latter, it is well established through isotopic labeling experiments that a symmetric allyl radical is an intermediate in the reaction and that its formation is rate-determining. Many studies simply extrapolate the results substantiated for this case to other reactions. New ideas on mechanisms are presented by Oyama, et oL, Parmaliana, et aL, and Laszlo. 

On the other hand, it is generally accepted that the redox properties of the selective oxidation catalysts control the oxygen activation as well as the surface stabilization of the oxygen activated species and their reactivity (19), In particular, the stabilization of active oxygen forms requires the presence of reduced sites on the surface. In fact, the peculiar behaviour of Mo, V and Fe oxides in selective oxidation reactions is strictly linked with the stabilization of reduced states (19), This point has stimulated a growing interest in providing correlation between the degree of reduction (32) or the extent of reduced sites (20) and the reactivity in... 

The oxidation of propene to acrolein has been one of the most studied selective oxidation reaction. The catalysts used are usually pure bismuth molybdates owing to the fact that these phases are present in industrial catalysts and that they exhibit rather good catalytic properties (1). However the industrial catalysts also contain bivalent cation molybdates like cobalt, iron and nickel molybdates, the presence of which improves both the activity and the selectivity of the catdysts (2,3). This improvement of performances for a mixture of phases with respect to each phase component, designated synergy effect, has recently been attributed to a support effect of the bivalent cation molybdate on the bismuth molybdate (4) or to a synergy effect due to remote control (5) or to more or less strong interaction between phases (6). However, this was proposed only in view of kinetic data obtained on a prepared supported catalyst. 

The viability of one particular use of a membrane reactor for partial oxidation reactions has been studied through mathematical modeling. The partial oxidation of methane has been used as a model selective oxidation reaction, where the intermediate product is much more reactive than the reactant. Kinetic data for V205/Si02 catalysts for methane partial oxidation are available in the literature and have been used in the modeling. Values have been selected for the other key parameters which appear in the dimensionless form of the reactor design equations based upon the physical properties of commercially available membrane materials. This parametric study has identified which parameters are most important, and what the values of these parameters must be to realize a performance enhancement over a plug-flow reactor. 

Although the methods illustrated above describe important steps toward the use of molecular oxygen in selective oxidation reactions, the need for cocatalysts increases the reaction s complexity and decreases the overall atom economy of the reaction [34,35]. It would be even more attractive if dioxygen could be used as the sole oxidant for Pd°. Indeed, early examples of direct dioxygen-coupled catalysis had been reported (Eqs. 9-11) [36-39], but prospects for this class of Pd-catalyzed oxidation reactions did not become widely appreciated until recently [12-18]. 

Oxides are widely exploited as catalysts for the selective oxidation of hydrocarbons. They provide lattice oxygen in selective oxidation reactions and exchange it with oxygen gas (e.g. from air in the reactant stream). The periodic lattice oxygen loss for the hydrocarbon oxidation occurs because of reducing gases, despite the presence of gas phase oxygen in the reactant stream. This results in the formation of anion vacancies, local non-stoichiometry and defect structures as discussed in chapter 1. 

The EM studies show that the novel glide shear mechanism in the solid state heterogeneous catalytic process preserves active acid sites, accommodates non-stoichiometry without collapsing the catalyst bulk structure and allows oxide catalysts to continue to operate in selective oxidation reactions (Gai 1997, Gai et al 1995). This understanding of which defects make catalysts function may lead to the development of novel catalysts. Thus electron microscopy of VPO catalysts has provided new insights into the reaction mechanism of the butane oxidation catalysis, catalyst aging and regeneration. 

The release and uptake of oxygen without essentially changing the basic bulk structure of the oxides are desirable in catalysis (Gai 1993) and efforts are in progress to use these oxides as catalysts in selective oxidation reactions of hydrocarbons. 

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