Supported catalysts molybdenum oxide

It was seen when studying mixed systems Pt-WOj/C and Pt-Ti02/C that with increasing percentage of oxide in the substrate mix the working surface area of the platinum crystallites increases, and the catalytic activity for methanol oxidation increases accordingly. With a support of molybdenum oxide on carbon black, the activity of supported platinum catalyst for methanol oxidation comes close to that of the mixed platinum-ruthenium catalyst. 

The cobalt-molybdenum combination was also investigated later by the Union Oil Company for the desulfurization of petroleum fractions (29). It was found that, for a bentonite-supported catalyst, cobalt oxide... 

Molybdenum oxide catalysts are prepared by heating the ammonium molybdate or by depositing molybdic acid on inert supports. The oxide prepared from the ammonium salt is somewhat dark colored due to a certaiu amount of reduction caused by the hot ammonia. However, the degree of activity of this material as a catalyst is apparently independent of the method of preparation, degree of oxidation, or supporting material. Yields of only about SO to 60 per cent of theoretical as phthalic anhydride are obtainable with this catalyst. Molybdenum oxides have the added... 

The Standard Oil patent (16) describes a supported reduced molybdenum oxide or cobalt molybdate on almnina, with the ethylene preferably contacting the catalyst in an aromatic solvent to affect the polymerization. Operating temperatures of 100-270°C were disclosed and the molecular weight could be varied from very high to low such as those of greases. 

For these reasons the design of a desulphurisation system must be undertaken with care. If the fuel cell plant has a source of hydrogen-rich gas (usually from the reformer exit), it is common practice to recycle a small amount of this back to a hydrodesulphurisation (HDS) reactor. In this reactor, any organic sulphur-containing compounds are converted, over a supported nickel-molybdenum oxide or cobalt-molybdenum oxide catalyst, into hydrogen sulphide via hydrogenolysis reactions of the type... 

The alkyl derivatives of thiazoles can be catalytically oxidized in the vapor phase at 250 to 400°C to afford the corresponding formyl derivatives (21). Molybdenum oxide, V2O5, and tin vanadate are used as catalysts either alone or with a support. The resulting carbonyl compounds can be selectively oxidized to the acids. 

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). 

Benzene-Based Catalyst Technology. The catalyst used for the conversion of ben2ene to maleic anhydride consists of supported vanadium oxide [11099-11-9]. The support is an inert oxide such as kieselguhr, alumina [1344-28-17, or sUica, and is of low surface area (142). Supports with higher surface area adversely affect conversion of benzene to maleic anhydride. The conversion of benzene to maleic anhydride is a less complex oxidation than the conversion of butane, so higher catalyst selectivities are obtained. The vanadium oxide on the surface of the support is often modified with molybdenum oxides. There is approximately 70% vanadium oxide and 30% molybdenum oxide [11098-99-0] in the active phase for these fixed-bed catalysts (143). The molybdenum oxide is thought to form either a soUd solution or compound oxide with the vanadium oxide and result in a more active catalyst (142). 

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. 

In catalytic toluene hydrodealkylation, toluene is mixed with a hydrogen stream and passed through a vessel packed with a catalyst, usually supported chromium or molybdenum oxides, platinum or platinum oxides, on siHca or alumina (50). The operating temperatures range from 500—595°C... 

Low pressure (0.1 to 20 MPa) and temperatures of 50 to 300°C using heterogeneous catalysts such as molybdenum oxide or chromium oxide supported on inorganic carriers to produce high density polyethylene (HDPE), which is more linear in nature, with densities of 0.94 to 0.97 g/cm. ... 

This process has many similarities to the Phillips process and is based on the use of a supported transition metal oxide in combination with a promoter. Reaction temperatures are of the order of 230-270°C and pressures are 40-80 atm. Molybdenum oxide is a catalyst that figures in the literature and promoters include sodium and calcium as either metals or as hydrides. The reaction is carried out in a hydrocarbon solvent. 

Olefin metathesis is the transition-metal-catalyzed inter- or intramolecular exchange of alkylidene units of alkenes. The metathesis of propene is the most simple example in the presence of a suitable catalyst, an equilibrium mixture of ethene, 2-butene, and unreacted propene is obtained (Eq. 1). This example illustrates one of the most important features of olefin metathesis its reversibility. The metathesis of propene was the first technical process exploiting the olefin metathesis reaction. It is known as the Phillips triolefin process and was run from 1966 till 1972 for the production of 2-butene (feedstock propene) and from 1985 for the production of propene (feedstock ethene and 2-butene, which is nowadays obtained by dimerization of ethene). Typical catalysts are oxides of tungsten, molybdenum or rhenium supported on silica or alumina [ 1 ]. 

The process has been commercially implemented in Japan since 1977 [1] and a decade later in the U.S., Germany and Austria. The catalysts are based on a support material (titanium oxide in the anatase form), the active components (oxides of vanadium, tungsten and, in some cases, of molybdenum) and modifiers, dopants and additives to improve the performance, especially stability. The catalyst is then deposited over a structured support based on a ceramic or metallic honeycomb and plate-type structure on which a washcoat is then deposited. The honeycomb form usually is an extruded ceramic with the catalyst either incorporated throughout the stmcture (homogeneous) or coated on the substrate. In the plate geometry, the support material is generally coated with the catalyst. 

Cover Illustration Atomic force microscopy image of molybdenum oxide particles on flat, silicon dioxide substrate, which serves as a model system for a supported catalyst. The area shown corresponds to one square micrometer the maximum difference in height is approximately 10 nanometer. The superimposed curve is the secondary ion mass spectrum of the model catalyst, showing the caracteristic isotopic patterns of single molybdenum ions and of molybdenum oxide cluster ions. 

Supported Rhodium Catalysts Alkali Promoters on Metal Surfaces Cobalt-Molybdenum Sulfide Hydrodesulfurization Catalysts Chromium Oxide Polymerization Catalysts... 

The high-density polyethylene is linear and can be manufactured by (i) coordination polymerisation of monomer by triethyl aluminium and tritanium chloride, (ii) polymerisation with supported Metal Oxide Catalysts. Such as chromium or molybdenum oxides supported over alumina-silica bases. 

Shen, Q Zhu, X., and Dong, J. (2009) Hydrodealkylation of C9-t aromatics to BTX over zeolite-supported nickel oxide and molybdenum oxide catalysts. Catal. Lett., 129, 170-180. 

A. Christodoulakis, E. Heracleous, A.A. Lemonidou and S. Boghosian, An operando Raman study of structure and reactivity of alumina-supported molybdenum oxide catalysts for the oxidative dehydrogenation of ethane, J. 

The oxidation of ethanol to acetic acid was among the first heterogeneous catalyzed reactions to be reported, but it has not attracted continued interest. During the 1990ies, however, 100% conversion of ethanol coupled with 100% selectivity to acetic acid was reported in a gas-phase reaction using molybdenum oxide catalytic systems on various supports, at temperatures below 250 Similarly, a tin oxide and molybdenum oxide catalyst was... 

In this paper selectivity in partial oxidation reactions is related to the manner in which hydrocarbon intermediates (R) are bound to surface metal centers on oxides. When the bonding is through oxygen atoms (M-O-R) selective oxidation products are favored, and when the bonding is directly between metal and hydrocarbon (M-R), total oxidation is preferred. Results are presented for two redox systems ethane oxidation on supported vanadium oxide and propylene oxidation on supported molybdenum oxide. The catalysts and adsorbates are stuped by laser Raman spectroscopy, reaction kinetics, and temperature-programmed reaction. Thermochemical calculations confirm that the M-R intermediates are more stable than the M-O-R intermediates. The longer surface residence time of the M-R complexes, coupled to their lack of ready decomposition pathways, is responsible for their total oxidation. 

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