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Kinetics selected metal oxides

Figure 3. Kinetics of H S sorption by selected metal oxides. Figure 3. Kinetics of H S sorption by selected metal oxides.
Abstract The redox properties of the metal oxides impart them peculiar catalytic activity which is exploited in reactions of oxidation and reduction of high applicative importance. It is possible to measure the extent of oxidation/reduction of given metal oxide by thermal methods which are become very popular TPR and TPO analyses. By successive experiments of reduction and oxidation (TPR-TPO cycles) it is possible to control the reversible redox ability of a given oxide in view of its use as catalyst. The two methods are here presented with explanation on some possibility of exploitation of kinetic study to derive quantitative information on the reduction/oxidation of the oxide. Examples of selected metal oxides with well-established redox properties which have been used in catalytic processes are shown. [Pg.175]

The multi-functionality of metal oxides1,13 is one of the key aspects which allow realizing selectively on metal oxide catalysts complex multi-step transformations, such as w-butane or n-pentane selective oxidation.14,15 This multi-functionality of metal oxides is also the key aspect to implement a new sustainable industrial chemical production.16 The challenge to realize complex multi-step reactions over solid catalysts and ideally achieve 100% selectivity requires an understanding of the surface micro-kinetic and the relationship with the multi-functionality of the catalytic surface.17 However, the control of the catalyst multi-functionality requires the ability also to control their nano-architecture, e.g. the spatial arrangement of the active sites around the first centre of chemisorption of the incoming molecule.1... [Pg.365]

In the previous sections of this review, it has been shown that most effective catalysts for the selective oxidation of propylene contain at least two types of metal oxides—an amphoteric or low-valence oxide, such as bismuth, tin, iron, or cobalt, and an oxide of a high valence metal, such as molybdenum or antimony. Moreover, it has been suggested several times that each of these metal oxide components may give rise to an active site for example, propylene may adsorb on an active site associated with one of the metal oxide components, and oxygen may adsorb on an active site associated with another metal oxide component. This problem has been studied using spectroscopic, adsorption, and kinetic techniques. It now seems appropriate to consider some of these studies in detail, attempting to relate the solid structure of the catalyst to the active sites wherever possible. [Pg.210]

Supported metal oxide catalysts are a new class of catalytic materials that are excellent oxidation catalysts when redox surface sites are present. They are ideal catalysts for investigating catalytic molecular/electronic structure-activity selectivity relationships for oxidation reactions because (i) the number of catalytic active sites can be systematically controlled, which allows the determination of the number of participating catalytic active sites in the reaction, (ii) the TOP values for oxidation studies can be quantitatively determined since the number of exposed catalytic active sites can be easily determined, (iii) the oxide support can be varied to examine the effect of different types of ligand on the reaction kinetics, (iii) the molecular and electronic structures of the surface MOj, species can be spectroscopically determined under all environmental conditions for structure-activity determination and (iv) the redox surface sites can be combined with surface acid sites to examine the effect of surface Bronsted or Lewis acid sites. Such fundamental structure-activity information can provide insights and also guide the molecular engineering of advanced hydrocarbon oxidation metal oxide catalysts such as supported metal oxides, polyoxo metallates, metal oxide supported zeolites and molecular sieves, bulk mixed metal oxides and metal oxide supported clays. [Pg.496]

Zhang YF, Vines F, Xu YJ, Li Y, Li JQ, lUas F (2006) Role of kinetics in the selective surface oxidations of transition metal carbides. J Phys Chem B 110 15454... [Pg.132]

A new experimental setup has recently been designed to study the chemical properties of size-selected metal clusters deposited on oxide substrates [210,211], Pd clusters have been produced by a laser evaporation source, ionized, then guided by ion optics through differentially pumped vacuum chambers and size-selected by a quadrupole mass spectrometer [210-212], The monodispersed clusters have been deposited with low kinetic energy (0,l-2eV) onto an MgO thin-film surface. The clusters-assembled materials obtained in this way exhibit peculiar activity and selectivity in the polymerization of acetylene to form benzene and aliphatic hydrocarbons [224], Figure 6 shows the temperature-programmed reaction (TPR) spectra for the cyclotrimerization of acetylene on supported Pd (1 30)... [Pg.121]

Oxidation of aqueous phenol solutions was studied over various catalysts in a semibatch slurry and continuous-flow fixed-bed reactors at temperatures up to 463 K and pressures slightly above atmospheric. The results show that due to a complex consecutive-parallel reaction pathway and a heterogeneous-homogeneous free-radical mechanism both kinetics and reaction selectivity are strongly dependent on the type of reactor used. Although the catalysts employed were found to be active in converting aqueous phenol solutions to nontoxic compounds, neither metal oxides nor zeolites were stable at the reaction conditions. [Pg.633]

Titanium-pillared montmorillonites (Ti-PILC) modified with tartrates were described as heterogeneous Sharpless epoxidation catalysts [33] as well as for the oxidation of aromatic sulfides [34]. Metal oxides modified with histamine showed modest efficiencies for the kinetic resolution of activated amino acid esters (kj /k5 2) [35]. Silica or alumina treated with diethylaluminium chloride and menthol catalyzed the Diels-Alder reaction between cylopentadiene and methacrolein with modest enantioselectivities of up to 31% ee [36]. ZeoHte HY, modified with chiral sulfoxides had remarkable selectivities for the kinetic resolution of 2-butanol (k /kj =39) but unfortunately the catalyst is not very stable... [Pg.1280]


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See also in sourсe #XX -- [ Pg.256 , Pg.258 ]




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Kinetic selection

Kinetic selectivity

Kinetics selection

Kinetics selectivity

Metalation selectivity

Oxidants kinetics

Oxidative kinetics

Oxide oxidation kinetics

Oxide, kinetics

Selective metallization

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