Oxidation supported metal oxide catalysts

Saravanamurugan, S., Palaniehamy, M., Arabindoo, B. and Murugesan, V. 2005. Solvent free synthesis of ehalcone and llavanone over zine oxide supported metal oxide catalysts. Catal. CommufL 6 399-403. 

The reaction is carried out over a supported metallic silver catalyst at 250—300°C and 1—2 MPa (10—20 bar). A few parts per million (ppm) of 1,2-dichloroethane are added to the ethylene to inhibit further oxidation to carbon dioxide and water. This results ia chlorine generation, which deactivates the surface of the catalyst. Chem Systems of the United States has developed a process that produces ethylene glycol monoacetate as an iatermediate, which on thermal decomposition yields ethylene oxide [75-21-8]. 

Physical adsorption—surface areas of any stable solids, e.g., oxides used as catalyst supports and carbon black Chemisorption—measurements of particle sizes of metal powders, and of supported metals in catalysts... 

Zheng, N.F. and Stucky, G.D. (2006) Ageneral synthetic strategy for oxide-supported metal nanoparticle catalysts. Journal of the American Chemical Society, 128 (44), 14278-14280. 

Another important and well studied paramagnetic ion in the lattice of oxide semiconductors is Zr3+ in Zr02. Zirconia dioxide is widely used both as a catalyst of different chemical processes, and as a carrier for constructing supported metal-complex catalysts. In the last years, sulfated zirconia attracted significant interest as an active and selective catalyst in skeletal isomerization of normal alkanes at low temperatures, cracking of paraffins, alkylation and acylation of aromatics [42, 53 and Refs therein]. The appropriate experimental data are collected in the following Table 8.2. 

However, PEG supported metal-free catalysts have also been shown to perform well in water. For example the synthesis of a PEG-supported TEMPO (2,2,6,6-tetramethyl-piperidine-l-oxyl), and its use as a highly efficient, recoverable and recyclable catalyst in oxidation reactions was described (Pozzi et al. 2004). 

Basset J-M, Lefebvre F, Santini C (1998) Surface organometallic chemistry Some fundamental features including the coordination effects of the support. Coord Chem Rev 178-180 1703 Gates BC (2000) Supported metal cluster catalysts. J Mol Catal A Chem 163 55 Fierro-Gonzalez JC, Kuba S, Hao Y, Gates BC (2006) Oxide- and zeoUte-supported molecular metal complexes and clusters Physical characterization and determination of structure, bonding, and metal oxidation state. J Phys Chem B 110 13326... 

N. F. Zheng, G. D. Stucky, A general strategy for oxide-supported metal nanoparticle catalysts, /. Am. Chem Soc. 128 (2006) 14278. 

CsOH was added as a promoter into several silica-supported metal (M) catalysts. The M/Cs/Si atomic ratio was 10/20/1000. The effect of metal (M) on the catalytic performance in the oxidation of methanol was studied. The reaction conditions were the same as those in the preceding section. The results are shown in Table 4. It was found that the Ag-CsOH/Si02 catalyst was the best among the CsOH promoted metal catalysts supported on sihca. 

Oxidation catalysts used in organic synthesis may essentially be divided into four classes homogeneous catalysts, supported metal catalysts, supported metal ion catalysts, and metal ion-incorporated solid matrices such as zeolites. Among metal-supported catalysts are the various transition metals supported on carbon, silica, etc. The third category consists essentially of ion-exchange resins which were considered separately in a previous section. The fourth category was also considered separately in another section. 

Redox zeolites such as TS-1, and supported metal ion catalysts such as those that use ion-exchange resins as supports are among the other major oxidation catalysts. These were considered earlier in this chapter. 

The chemical bonding features of metal sulfide surfaces are related to those of the reducible oxides. We discuss in detail a key question for supported metal sulfide catalysts What is the state of the sulfide edge sites under catalytic conditions and the shape of the sulfide particles In addition, we attempt to help elucidate the role of ions such as Ni + or Co + in promoting reactivity for sulfide systems such as M0S2. 

Physical adsorption isotherms involve measuring the volume of an inert gas adsorbed on a material s surface as a function of pressure at a constant temperature (an isotherm). Using nitrogen as the inert gas, at a temperature close to its boiling point (near 77K), such isotherms are used to determine the amount of the inert gas needed to form a physisorbed monolayer on a chemically unreactive surface, through use of the Brunauer, Emmett, and Teller equation (BET). If the area occupied by each physisorbed N2 molecule is known (16.2A ), the surface area can then be determined. For reactive clean metals, the area can be determined using chemisorption of H2 at room temperature. Most clean metals adsorb one H atom per surface metal atom at room temperature (except Pd, which forms a bulk hydride), so if the volume of H2 required for chemisorption is measured, the surface area of the metal can be determined if the atomic spacings for the metal is known. The main use of physical adsorption surface area measurement is to determine the surface areas of finely divided solids, such as oxide catalyst supports or carbon black. The main use of chemisorption surface area measurement is to determine the particle sizes of metal powders and supported metals in catalysts. 

In comparison to metal oxide catalysts, very few Raman studies of supported metal sulfide catalysts have appeared in the catalysis literature. This is due to the relatively weak Raman signals from the dark metal sulfide phases and the corrosive nature of the H2S environment required for in situ studies. Furthermore, the Raman spectra of supported metal sulfide catalysts have not been exceptionally informative, especially on a molecular level, because they primarily provide information about the crystalline MS2 phases present... 

Raman spectroscopy has made a significant impact on HDS catalysts because it is now recognized that the final state of the supported metal sulfide catalyst is directly related to the initial state of the supported metal oxide catalyst [143]. In other words, the molecular design of HDS catalysts is controlled during the synthesis of the supported metal oxide catalysts, which can be readily monitored with Raman spectroscopy (see Sec. III). 

Impact of NO on the decomposition of supported metal nitrate catalyst precursors and the final metal oxide dispersion... 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Oxidation of methanol to formaldehyde with vanadium pentoxide catalyst was first patented in 1921 (90), followed in 1933 by a patent for an iron oxide—molybdenum oxide catalyst (91), which is stiU the choice in the 1990s. Catalysts are improved by modification with small amounts of other metal oxides (92), support on inert carriers (93), and methods of preparation (94,95) and activation (96). In 1952, the first commercial plant using an iron—molybdenum oxide catalyst was put into operation (97). It is estimated that 70% of the new formaldehyde installed capacity is the metal oxide process (98). 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

Fixed-Bed Vapor-Phase Oxidation of Naphthalene. A sihca gel or sihcon carbide support is used for catalyst involved in the oxidation of naphthalene. The typical naphthalene oxidation catalyst is a mixture of vanadium oxide and alkali metal sulfate on the siUca support. Some changes, such as the introduction of feed vaporizers, are needed to handle a naphthalene feed (14), but otherwise the equipment is the same. 

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