Metal oxides catalytic activity

Burya, A. 1. Naphadzokova, L. Kh. Kozlov, G. V. Description of metal oxides catalytic activity within the frameworks of synergetics. Proceedings of IV-th Ukranian Polish Scientific Conf. "The Polymers of Special Application . Dnepropetrovsk, DSU, 2006, 88. 

Wachs, I. and Roberts, C. (2010). Monitoring Surface Metal Oxide Catalytic Active Sites with Raman Spectroscopy, Chem. Soc. Rev., 39, pp. 5002-5017. 

Hi. Cr, Mo, W. In contrast to group IV and V transition metals, the catalytic active oxidant is of another type for group VI transition metal-catalyzed epoxidations The transition-metal-oxo complexes, in which the oxygen that is transferred is bonded to the metal via a double bond, are the active oxidizing species. 

Selective partial oxidation of hydrocarbons poses considerable challenges to contemporary research. While by no means all, most catalytic oxidations are based on transition-metal oxides as active intermediates, and the oxidative dehydrogenation of ethylbenzene to styrene over potassium-promoted iron oxides at a scale of about 20 Mt/year may serve as an example [1]. Despite this... 

The effects of adding various metal ions and metal complexes on the rate of a model oxidation reaction have been studied in some detail The model reaction chosen—the oxidation of ethanethiol in aqueous alkaline solution in the presence of metal-containing catalysts—involves the transfer of an electron from the thiol anion to the metal The catalytic activity of additives depends upon the solubility of the particular metal complex and varies according to the nature of the ligand attached to the metal ion. In conjunction with different metals, the same ligand can act either as a catalyst or as an inhibitor. The results are discussed in the light of proposed reaction mechanisms. 

For a better understanding of the factors that play a role in the catalytic selective reduction of nitrobenzene to nitrosobenzene some pieces of relevant information from previous work have to be considered. Favre et al.l6] found that oxides of various transition metals show catalytic activity in the mentioned reaction and a-Mn304 (Hausmannite) appeared to be the most active and selective catalyst. The function of nitrobenzene as an internal reducing agent has already been suggested by Zengell,] and is confirmed by Favre et al. Nitrobenzene can thus reduce as well as oxidize the catalyst... 

The first step in the reaction is the formation of the catalytically active species and then coordination with the hydroperoxide. This is followed by the ratedetermining oxygen-transfer step, for which two reaction pathways have been suggested. One of these is a mechanism involving a metal-oxide-containing active species, while the other involves an activated complex between the catalyst and the intact hydroperoxide molecule. The latter is confirmed by experiments with 0-enriched water and by the results of the steric effects. 

The present investigation was conducted to identify and determine the degree of Rh-base metal oxide interaction, using unsupported rhodium oxides and bulk aluminum and rare earth metal rhodates. Catalytic activities were determined using monolithic catalysts containing various bulk rhodium species exposed to a simulated stoichiometric auto exhaust composition. The activities were correlated with information obtained from CO chemisorption measurements, temperature-programmed reduction,... 

Nobel metal based catalysts such as Pt, Pd, Rh and Ir has been reported to exhibit considerable activities in this process [3-4], Because of higher activities Pd and Pt based catalysts are most widely used, however Pd based catalysts have been reported to be catalytically more active than Pt in this process and therefore most of the recent researches have focused on Pd as the active component [5-7], As a matter of fact, properties of the metal oxide catalytic supports also play an important role in the catalytic processes. 

In conclusion, partially dehydroxylated oxide surfaces exhibit a large inventory of surface OH groups and water molecules together with Lewis acidic and Lewis basic sites with coordinative unsaturation (structures II and III of Scheme 1). The hydroxyl population is the souree of protons that cause enhanced surface electrical conductivity and catalytic activity. It is significant that the increase in the conductivity value is paralleled by increases in either the amount of weakly bound protons or their mobility [48]. Almost all metal oxides are active in catalytic isomerization of alkenes, which is one of the least demanding reactions in terms of the requirements for the acid strength of active sites [34]. Studies on several oxide systems show that the activity is lost after extensive dehydration and is partially restored by... 

Metal oxide catalytic materials currently find wide application in the petroleum, chemical, and environmental industries, and their uses have significantly expanded since the mid-20th century (especially in environmental applications) [1,2], Bulk mixed metal oxides are extensively employed by the chemical industries as selective oxidation catalysts in the synthesis of chemical intermediates. Supported metal oxides are also used as selective oxidation catalysts by the chemical industry, as environmental catalysts, to selectively transform undesirable pollutants to nonnox-ious forms, and as components of catalysts employed by the petroleum industry. Zeolite and molecular sieve catalytic materials are employed as solid acid catalysts in the petroleum industry and as aqueous selective oxidation catalysts in the chemical industry, respectively. Zeolites and molecular sieves are also employed as sorbents for separation of gases and to trap toxic impurities that may be present in water supplies. Significant molecular spectroscopic advances in recent years have finally allowed the nature of the active surface sites present in these different metal oxide catalytic materials to be determined in different environments. This chapter examines our current state of knowledge of the molecular structures of the active surface metal oxide species present in metal oxide catalysts and the influence of different environments upon the structures of these catalytic active sites. 

In catalysis, oxides with well defined acidic and basic properties are used in different forms that have found application in numerous catalytic applications in the gas-solid and liquid-solid heterogeneous catalysis [3, 46, 47], Among the most used oxide materials in catalysis, we And (i) bulk oxides (one component metal oxides) (ii) doped and moditied oxides (iii) supported metal oxides (dispersed active oxide component onto a support oxide component) (iv) bulk and supported binary metal oxides to quaternary metal oxides (mixed oxide compositions) (v) complex oxides (e.g., spinels, perovskites, hexa-aluminates, bulk and supported hydrotalcites, pillared clays, bulk and supported heteropolyacids, layered silicas, etc.). 

Several approaches to form Pd°/Pd in active site are investigated. Highly uniform distribution of Pd may serve as one of the reason of high activity of catalysts supported on UDD in HDC of chlorinated derivatives of benzene. Use of modified zirconia as support leads to formation of intermetallic oxide Pd-Zr-0, which results in active and stable hydrodechloriration catalyst. Addition of second non-noble metal improves catalytic activity by formation of bimetallic alloy and at the same time decreases Pd poisoning by chlorine. 

Chemical Properties. Higher a-olefins are exceedingly reactive because their double bond provides the reactive site for catalytic activation as well as numerous radical and ionic reactions. These olefins also participate in additional reactions, such as oxidations, hydrogenation, double-bond isomerization, complex formation with transition-metal derivatives, polymerization, and copolymerization with other olefins in the presence of Ziegler-Natta, metallocene, and cationic catalysts. All olefins readily form peroxides by exposure to air. 

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

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