Transition metal oxidation catalysts

We have summarized below recent results concerning spectroscopic / flow reactor investigations of hydrocarbons partial and total oxidation on different transition metal oxide catalysts. The aim of this study is to have more information on the mechanisms of the catalytic activity of transition metal oxides, to better establish selective and total oxidation ways at the catalyst surface, and to search for partial oxidation products from light alkane conversion. 

However, in the same temperature range and O2 partial pressure total oxidation of acrolein and propene largely predominates. This can be taken as a further support that on transition metal oxide catalysts the same oxygen species (lattice oxygen) are involved in both partial and total oxidation. 

Bruckner, A. and Kondratenko, E. (2006) Simultaneous operando EPR/UV-vis/laser-Raman spectroscopy - A powerful tool for monitoring transition metal oxide catalysts during reaction, Catal. Today, 113, 16. 

The hydrogen-bonding interactions within the complexes W2CI4-(y-OR)2(OR)2(ROH)2 and V Cli y-OR)2(ORT)2(Rf0H)2 may provide the molecular analogues with which to model the structure and reactivities of transition metal oxide catalysts that possess surface hydroxyl groups. The thermal treatment which is often carried out in the pretreatment of metal oxides (leading to the loss of -OH... 

Krajnc, M. and Levee, J., Oxidation of phenol over transition-metal oxide catalyst in supercritical water, Indust. Eng. Chem. Res., 36, 32439-3445, 1997b. 

EPR studies of transition metal-oxide catalysts have shown that oxygen molecules and atoms on their surface form radicals of several types whose parameters are mainly listed in Table 8.3. Here and in further Tables, for better comparison and representation, we include the appropriate data obtained for some diamagnetic oxides and relative compounds. 

Bruckner A. Simultaneous combination of in situ-EPR/UV-VIS/on line GC a novel setup for investigating transition metal oxide catalysts under working conditions. Chem Com-mun. 2001 2122. 

Analytical Chemistry of the Transition Elements Coordination Numbers Geometries Coordination Organometallic Chemistry Principles Hydride Complexes of the Transition Metals Oxide Catalysts in Sohd-state Chemistry Periodic Table Trends in the Properties of the Elements Sol Gel Synthesis of Solids Structure Property Maps for Inorganic Solids Titanium Inorganic Coordination Chemistry Zirconium Hafnium Organometallic Chemistry. 

Although this chapter focuses on oxidation reactions involving redox supported vanadium oxide catalysts, similar trends with surface coverage and specific oxide support also apply for other redox supported transition metal oxide catalysts, such as supported M0O3 [51], CrOs [52] and Re207 [53], The redox supported vanadium oxide catalytic system was chosen for this review because of the extensive studies that these catalysts have received in recent years as well as their widespread industrial appHcations. 

Isolation and identification of surface-bonded acetone enolate on Ni(l 11) surfaces show that metal enolate complexes are key intermediates in carbon-carbon bond-forming reactions in both organometaUic chemistry and heterogeneous catalysis. Based on studies on powdered samples of defined surface structure and composition, most of the results were reported for acetone condensation over transition-metal oxide catalysts, as surface intermediate in industrially important processes. With the exception of a preoxidized silver surface, all other metal single-crystal surfaces have suggested that the main adsorption occurs via oxygen lone-pair electrons or di-a bonding of both the carbonyl C and O atoms. 

Figure 6.5 shows the yields ([wt%]) of the reaction of PET using several transition metal oxide catalysts under the following conditions a temperature of 500°C, a time factor (the ratio of the mass of the catalyst W, to the PET feed rate F) of 0.317 h, and a particle size of 0.21-0.25 mm. Fc203 did not show activity, hence these results have been omitted. With respect to the reduction of terephthalic acid, FeOOH, nickel hydroxide and nickel oxide showed the decomposition activity of terephthahc acid. However, a large amount of benzoic acid, which is also a sublimate material (sublimation point 100°C), was produced over nickel hydroxide and nickel oxide. Because these nickel compounds are more expensive than FeOOH, FeOOH was considered to be a suitable catalyst for the decomposition of terephthalic acid. 

This paper is primarily concerned with systems based on both homogeneous and heterogeneous (bulk and supported) Z-N catalysts. Transition metal oxide catalysts are not covered due to a different mechanism of their action [e.g. 3>], although some of methods have a universal applicability. 

Baltes, M., O. Collar , P. Van Der Voort, and E. F. Vansant, Synthesis of Supported Transition Metal Oxide Catalysts by the Designed Deposition of Acetylacetonate Complexes , Langmuir (1999), 15, 5841-5. 

Zemski KA, Justes DR, Castleman AW Jr (2002) Studies of metal oxide clusters Elucidating reactive sites responsible for the activity of transition metal oxide catalysts. J Phys Chem B 106 6136... 

In spite of the drawbacks, gold has still some advantages, being more selective for N2 than the PGM catalysts and less susceptible to the deleterious effects of moisture than most ordinary transition metal oxide catalysts [132]. 

Stabilization of Foods. The oxidation of food containing fats and oils results in a loss of sensory appeal and eventually rancidness. FDA regulations covering the use of direct food additives are stringent and few new materials have been regulated. A number of products in use today, such as citric acid (33), and CC-tocopherol [59-02-9] (41), are in the GRAS list. The most commonly used materials are butylated hydroxytoluene [128-37-0] (1), -propyl gallate [129-79-9] (42), a-tocopherol, and butylated hydroxyanisole [25013-16-5] (43). The concentrations allowed in food are less than 0.02%. Metal deactivators such as citric acid (33), ethylenediaminetetraacetic acid (32) and its salts, and calcium chelate are used to deactivate transition metal oxidation catalysts. 

The catalytic activity of the catalysts for the ORR is screened using a rotating-disk electrode (RDF) method. The activity of the new transition metal oxide catalysts is estimated by comparison to a standard RDE of 10 weight % platinumWulcan carbon, XC-72 (PtWC) catalyst (Alfa). The electrocatalytic activity of the catalysts are compared in Tafel plots of potential vs. current, calculated from the electrochemical data as described in the literature. 

The best performance data were reported by Sofranko and Jones using a catalyst of 15 wt% Mn promoted with 5 wt% Na PjO on SiOj, a modified transition metal oxide catalyst. Conversion of 26% and Cgt selectivity of 93% were obtained after co-feeding of 5 mol% CHjCl over two to three cycles. The reaction conditions were 750 C, 1 atm, and 900-L/h GHSV. A total of 53 cycles was accumulated. Sofranko obtained 17% conversion and 88% selectivity at 825 C and 600-L/h GHSV using a catalyst of 13 wt% NaMnO on MgO. 

Transition Metal Oxide Catalysts, Proc. Nat. Symp. Heterogen. Catal. Control Air Pollut., 1st (Philadelphia, November, 1963). 

Klimisch, R. L. "Oxidation of CO and Hydrocarbons over Supported Transition Metal Oxide Catalysts", Proceedings of the 1st National Symposium on Heterogeneous Catalysis for Control of Air Pollution, Philadelphia, Franklin Institute, November, 1963. 

Reduced Transition Metal Oxide Catalysts on Support... 

The Ziegler process yields polyethylene as low as 0.94 g/cm in density, but process modifications can result in products with a density of 0.965 g/cm. The transition metal oxide catalysts on support, on the other hand, yield products in the density range of 0.960-0.970 g/cm. ... 

Many copolymers of ethylene with a-olefins are prepared commercially. Thus ethylene is copolymerized with butene-1, where a comonomer is included to lower the regularity and the density of the polymer. Many copolymers are prepared with transition metal oxide catalysts on support. The comonomer is usually present in approximately 5% quantities. This is sufficient to lower the crystallinity and to markedly improve the impact strength and resistance to environmental stress cracking. Copolymers of ethylene with hexene-1, where the hexene-1 content is less than 5%, are also produced for the same reason. 

The transition metal oxide catalysts on support, such as the CrOa/silica-alumina (Phillips) and M0O3/AI2O3 (Standard Oil), are used to copolymerize minor quantities of a-olefins with ethylene. Such copolymerizations introduce short pendant groups into polymer backbones. 

The water gas shift reaction involves the conversion of water and carbon monoxide into hydrogen and carbon dioxide, typically using a heterogeneous transition metal-oxide catalyst (Scheme 12.1). The reaction is reversible, and under certain conditions the reaction can operate in either the forwards (hydrogen production) or reverse (carbon monoxide production) direction. Promoted iron-oxide catalysts are most prevalent in WGS chemistry, although, by comparison, platinum-group metals exhibit a greater catalytic activity. ... 

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