Oxidation catalyst application

Noble metals are defined herein as Pt, Pd, Ag, and Au. These noble metals are frequently alloyed with the closely related metals Ru, Rh, Os, and Ir, and they are usually supported on an oxide support such as 7-AI2O3 or SiO. Although in principle any of these metals may be used as oxidation catalysts, in most practical systems only Pt, Pd, and a few alloys are used because the generally high temperatures employed for most oxidation catalyst applications (e.g., catalytic incineration, automotive exhaust catalysts) can cause sintering, volatility loss, and irreversible oxidation of the other metals. Limited supply and the resulting high cost of these other metals also minimizes their use. As a result, most reported research deals with supported Pt and Pd (and alloys of these with other metals). 

Briand, L., Hirt, A. and Wachs, I. (2001). Quantitative Determination of the Number of Surface Active Sites and the Turnover Frequencies for Methanol Oxidation over Metal Oxide Catalysts Application to Bulk Metal Molybdates and Pure Metal Oxide Catalysts, J. Catal., 202, pp. 268-278. 

Briand, L.E., Hirt, A.M., and Wachs, I.E. Quantitative determination of the number of surface active sites and the turnover frequencies for methanol oxidation over metal oxide catalysts Application to bulk metal molybdates and pure metal oxide catalysts. J. Catal. 2001, 202, 268-278. 

Coating metallic foams and strnctnred reactors by V0x/Ti02 oxidation catalyst Application ofRPECVD... 

Besides stmctural variety, chemical diversity has also increased. Pure silicon fonns of zeolite ZSM-5 and ZSM-11, designated silicalite-l [19] and silicahte-2 [20], have been synthesised. A number of other pure silicon analogues of zeolites, called porosils, are known [21]. Various chemical elements other than silicon or aluminium have been incoriDorated into zeolite lattice stmctures [22, 23]. Most important among those from an applications point of view are the incoriDoration of titanium, cobalt, and iron for oxidation catalysts, boron for acid strength variation, and gallium for dehydrogenation/aromatization reactions. In some cases it remains questionable, however, whether incoriDoration into the zeolite lattice stmcture has really occurred. 

Benzaldehyde is easily oxidised by atmospheric oxygon giving, ultimately, benzoic acid. This auto-oxidation is considerably influenced by catalysts tiiose are considered to react with the unstable peroxide complexes which are the initial products of the oxidation. Catalysts which inhibit or retard auto-oxidation are termed anti-oxidants, and those that accelerate auto-oxidation are called pro-oxidants. Anti-oxidants find important applications in preserving many organic compounds, e.g., acrolein. For benzaldehyde, hydroquinone or catechol (considerably loss than U-1 per cent, is sufficient) are excellent anti-oxidants. 

As a final example of the application of gas-liquid-particle operation to a process involving a gaseous reactant and a solid catalyst, the possibility of polymerizing ethylene in, for example, a slurry operation employing a metal or metal oxide catalyst can be cited. It has been suggested that the good control of reaction conditions obtained in a slurry-type operation may be of importance in the production of certain types of polyethylene (Rl). 

The possibility of application of the NEMCA effect in conventional flow reactors and of its extension to oxide catalysts may be of great importance in the future, though both the nature of the migrating, spillover species and their effect on the molecular-scale mechanism require further studies B. Grzybowska-SwierkoszandJ. Haber, Annual Reports on Chemistry, 1994)... 

Recycle of HBr to bromine is highly desirable both from an economic and an environmental standpoint. Catalytic oxidation offers the potential to recycle HBr from contaminated waste streams to bromine. We have demonstrated that the oxidation catalyst is stable against deactivation by a wide range of contaminants found in waste HBr streams. Strategies to deal with the contaminants will depend on the recycle applications in which the catalytic oxidation unit serves. 

Several researchers have focused their attention on the application of oxide materials to lower the oxidation temperature of soot particulates. It was reported that active soot oxidation catalysts are PbO, C03O4, V2O5, M0O3, CuO, and perovskite type oxides[3]. 

Titanium dioxide supported gold catalysts exhibit excellent activity for CO oxidation even at temperatures as low as 90 K [1]. The key is the high dispersion of the nanostructured gold particles over the semiconducting Ti02 support. The potential applications of ambient temperature CO oxidation catalysts include air purifier, gas sensor and fuel cell [2]. This work investigates the effects of ozone pretreatment on the performance of Au/Ti02 for CO oxidation. 

Understanding and controlling oxide surfaces are the key issues for the development of industrial oxide catalysts, but oxide surfaces are in general heterogeneous and complicated, and hence have been little studied so as to put them on a scientific basis by traditional approaches. While studies of the structure of surfaces have focused on metals and semiconductors over the past thirty years, the application of surface science techniques to metal oxides has blossomed only within the last decade[l-3]. 

Acid-base reactivity is an important property of oxide catalysts, and its control is of interest in surface chemistry as well as being of importance in industrial applications. The exposed cations and anions on oxide surfaces have long been described as acid-base pairs. The polar planes of ZnO showed dissociative adsorption and subsequent decomposition of methanol and formic acid related with their surface acid-base properties[3]. Further examples related to the topic of acid-base properties have been accumulated to date[ 1,4-6]. 

Process Miniaturization Second International Conference, CATTECH, December 1998 Steep progress in microelectronics in the past key players topics of IMRET 2 general advantages of micro flow energy, safety, process development, combinatorial catalyst testing, lab-on-a-chip biological applications anodically oxidized catalyst supports as alternatives to non-porous supports [220]. 

The oxides often are nonstoichiometric (with an excess or dehcit of oxygen). Many oxides are semiconducting, and their conductivity can be altered by adding various electron donors or acceptors. Relative to metals, the applications of oxide catalysts in electrochemistry are somewhat limited. Cathodic reactions might induce a partial or complete reduction of an oxide. For this reason, oxide catalysts are used predominantly (although not exclusively) for anodic reactions. In acidic solutions, many base-metal oxides are unstable and dissolve. Their main area of use, therefore, is in alkaline or neutral solutions. 

At an industrial scale, the esterification catalyst must fulfill several conditions that may not seem so important at lab-scale. This must be very active and selective as by-products are likely to render the process uneconomical, water-tolerant and stable at relatively high temperatures. In addition, it should be an inexpensive material that is readily available on an industrial scale. In a previous study we investigated metal oxides with strong Bronsted acid sites and high thermal stability. Based on the literature reviews and our previous experimental screening, we focus here on application of metal oxide catalysts based on Zr, Ti, and Sn. 

Despite these limitations, the application of an oxidation catalyst has a strong positive effect on the SCR performance (Figure 9.14) [14]. 

CoSalen Y carries oxygen as a cargo.72 The catalytic properties of the zeolite-encapsulated metal complexes depend mainly on the complexed metal atoms, which are used usually as oxidation catalysts but other applications are also beginning to emerge. The zeolite-encapsulated catalysts can be regarded as biomimetic oxidation catalysts.73 In liquid-phase oxidation reactions catalyzed... 

The increasing volume of chemical production, insufficient capacity and high price of olefins stimulate the rising trend in the innovation of current processes. High attention has been devoted to the direct ammoxidation of propane to acrylonitrile. A number of mixed oxide catalysts were investigated in propane ammoxidation [1]. However, up to now no catalytic system achieved reaction parameters suitable for commercial application. Nowadays the attention in the field of activation and conversion of paraffins is turned to catalytic systems where atomically dispersed metal ions are responsible for the activity of the catalysts. Ones of appropriate candidates are Fe-zeolites. Very recently, an activity of Fe-silicalite in the ammoxidation of propane was reported [2, 3]. This catalytic system exhibited relatively low yield (maximally 10% for propane to acrylonitrile). Despite the low performance, Fe-silicalites are one of the few zeolitic systems, which reveal some catalytic activity in propane ammoxidation, and therefore, we believe that it has a potential to be improved. Up to this day, investigation of Fe-silicalite and Fe-MFI catalysts in the propane ammoxidation were only reported in the literature. In this study, we compare the catalytic activity of Fe-silicalite and Fe-MTW zeolites in direct ammoxidation of propane to acrylonitrile. 

In the 1990s and beyond 2000, there has been an explosion of interest in metal/ partially reducible oxide catalysts for low temperature water-gas shift, mainly directed at the production/purification of hydrogen in a fuel processor for fuel cell applications. 

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