Chemical metal oxide catalysts

Chemical Properties. On thermal decomposition, both sodium and potassium chlorate salts produce the corresponding perchlorate, salt, and oxygen (32). Mixtures of potassium chlorate and metal oxide catalysts, especially manganese dioxide [1313-13-9] Mn02, are employed as a laboratory... 

A 5 wt.% CoOx/Ti02 catalyst was prepared via an incipient wetness technique in which an aqueous solution of Co(N03)2 6H20 (Aldrich, 99.999%) was impregnated onto a shaped Ti02 (Milleimium Chemicals, commercially designated as DT51D, 30/40 mesh), as described in detail elsewhere [6]. Other supported metal oxide catalysts, such as FeOx, CuO, and NiOx, were obtained in a fashion similar to that used for preparing the CoO, catalyst. 

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... 

The newest and most commercially successful process involves vapor phase oxidation of propylene to AA followed by esterification to the acrylate of your choice. Chemical grade propylene (90—95% purity) is premixed with steam and oxygen and then reacted at 650—700°F and 60—70 psi over a molybdate-cobait or nickel metal oxide catalyst on a silica support to give acrolein (CH2=CH-CHO), an intermediate oxidation product on the way to AA. Other catalysts based on cobalt-molybdenum vanadium oxides are sometimes used for the acrolein oxidation step. 

Light hydrocarbons consisting of oxygen or other heteroatoms are important intermediates in the chemical industry. Selective hydrocarbon oxidation of alkenes progressed dramatically with the discovery of bismuth molybdate mixed-metal-oxide catalysts because of their high selectivity and activity (>90%). These now form the basis of very important commercial multicomponent catalysts (which may contain mixed metal oxides) for the oxidation of propylene to acrolein and ammoxidation with ammonia to acrylonitrile and to propylene oxide. 

Basic oxides such as La203 and mixtures like Li20(5% by weight)-MgO have important potential as catalysts in the oxidative coupling of methane.13 Large reserves of methane are available in the form of natural gas and could serve as feedstock for production of many organic chemicals rather than as a mere fuel, but the CH4 molecule is exasperatingly unreac-tive in most circumstances. With basic metal oxide catalysts at 600-900 °C,... 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

Catalytic oxidation is the most important technology for the conversion of hydrocarbon feedstocks (olefins, aromatics and alkanes) to a variety of bulk industrial chemicals.1 In general, two types of processes are used heterogeneous, gas phase oxidation and homogeneous liquid phase oxidation. The former tend to involve supported metal or metal oxide catalysts e.g. in tne manufacture of ethylene oxide, acrylonitrile and maleic anhydride whilst the latter generally employ dissolved metal salts, e.g. in the production of terephthalic acid, benzoic acid, acetic acid, phenol and propylene oxide. 

Nijhuis TA, Tinnemans SJ, Visser T, Weckhuysen BM. Operando spectroscopic investigation of supported metal oxide catalysts by combined time-resolved UV-VIS/ Raman/on-line mass spectrometry. Physical Chemistry Chemical Physics 2003, 5, 4361 1365. 

Tinnemans SJ, Kox MHF, Nijhuis TA, Visser T, Weckhuysen BM. Real time quantitative Raman spectroscopy of supported metal oxide catalysts without the need of an internal standard. Physical Chemistry Chemical Physics 2005, 7, 211-216. 

The enthalpies of combustion, formation, and isomerization of car-2-ene and car-3-ene have been reported 335 the activation energy for the titanium-catalysed first-order isomerization of car-3-ene into car-4-ene and various menthadienes is 20kcalmor1 at 150—160 °C.336 Isomerization of car-3-ene over metal oxide catalysts varies substantially depending upon the metal catalyst used 337 other Russian work reports diene formation from the vapour-phase isomerization of car-3-ene but this Reporter is unable to assess the significance of the work from Chemical Abstracts in the absence of the original paper.338... 

Furfural 69 has been used as a chemical feedstock for the production of furan via two production methods involving the decarbonylation of furfural <2005MI7>. Processes in both the liquid and gas phases were described for the preparation of furan through the decarbonylation of furfural using noble metal and metal oxide catalysts. The results of the study led the authors to state that the research trends for preparing furan based on the decarbonylation of furfural should mainly be concentrated on more effective catalysts and environmentally friendly processes. 

Metal oxide catalysis continues to grow at a rapid rate, reflecting the wide range of chemical reactions that can be enhanced by the use of a metal oxide catalyst. The advances in characterization techniques and their application to the field have improved our understanding of the processes occurring on the surface and in the bulk. This two volume review series is therefore timely. 

Chemical Reactions. - Probe reactions can be quite useful in the characterization of the surface condition of the supported metal oxide catalyst when there exist an unambiguous relationship between the property to be tested and the surface structure responsible for that property. Often, the issue of demanding... 

Some of the oxides of vanadium and molybdenum catalyze the selective oxidation of hydrocarbons to produce valuable chemical intermediates. In a reaction path proposed by Mars and van Krevelen (see Section 10.5), the hydrocarbon first reduces the surface of the metal oxide catalyst by reaction with lattice oxygen atoms. The resulting surface vacancies are subsequently re-oxidized by gaseous O2. The elementary steps of this process are shown below. Electrons are added to the sequence to illustrate the redox nature of this reaction. 

The production of formaldehyde still relies on the chemical process developed nearly 50 years ago. Nearly 70% of new installations in the US utilize a metal oxide catalyst to form formaldehyde bv the oxidation of methanol... 

F. S. Stone, in Chemistry and Chemical Engineering of Catalytic Processes, R. Prins, G. C. A. Schuit, eds., Sijthoff and Noordhoff, Alphen an den Rijn, The Netherlands, 1980. Structures of metal oxide catalysts. 

One of the best ways of characterizing a supported catalyst is determination of dispersion and effective surface area of the catalyticaUy active component. The dispersion of metal oxide catalysts can be determined by selective chemisorption of oxygen at appropriate temperatures [14-16]. The dispersions obtained from oxygen chemisorption measurements on various catalysts are presented in table 1. The N2 BET surface areas of various samples are also shown in this table. As can be noted, dispersion for 20 wt% catalyst is similar, within experimental limitations, irrespective of their origin. The BET surface area measurements also reveal that both the preparation methods yield similar type of catalysts in terms of physico-chemical characteristics. These catalysts were further evaluated for selective oxidation of / -methox doluene to p-... 

Metal oxides are widely used as catalyst supports but can also be catalytically active and useful in their own right. Alumina, for example, is used to manufacture ethene from ethanol by dehydration. Very many mixed metal oxide catalysts are now used in commercial processes. The best understood and most interesting of these are zeolites that offer the particular advantage of shape selectivity resulting from their narrow microporous pore structure. Zeolites are now used in a number of large-scale catalytic processes. Their use in fine chemical synthesis is discussed in Chapter 2. 

Sulfated metal oxide catalysts represent a class of extremely attractive strong solid acids showing widespread application in different areas of chemical fransformafions. It was reported that sulfated zirconia (SZ) prepared by treatment of zirconia with sulfuric acid or ammonium sulfafe exhibifs exfremely sfrong acidity, and it is able to catalyze the isomerization of bufane to isobutane at room temperature. This behavior... 

Metal oxide catalysts are extensively employed in the chemical, petroleum and pollution control industries as oxidation catalysts (e.g., oxidation of methanol to formaldehyde, oxidation of o-xylene to phthalic anhydride, ammoxidation of propylene/propane to acrylonitrile, selective oxidation of HjS to elemental sulfur (SuperClaus) or SO2/SO3, selective catalytic reduction (SCR) of NO, with NHj, catalytic combustion of VOCs, etc.)- A special class of metal oxide catalysts consists of supported metal oxide catalysts, where an active phase (e.g., vanadium oxide) is deposited on a high surface area oxide support (e.g., alumina, titania, ziiconia, niobia, ceria, etc.). Supported metal oxide catalysts provide several advantages over bulk mixed metal oxide catalysts for fundamental studies since (1) the number of surface active sites can be controlled because the active metal oxide is 100% dispersed on the oxide support below monolayer coverage,... 

Later it was shown that sequential introduction of CH4 and O2 was not necessary to promote methane oxidative dimerization but this could be achieved directly by passing CH4/O2 mixtures over a metal oxide catalyst [57]. Since these early reports, work directed towards investigating the chemical oxidative dimerization of methane has increased with a significant number of papers [58-88] and reviews [89, 90] being published. 

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