Molybdenum oxide promoter

With aromatic compounds conditions can be found so that ring oxidation predominates and phenolic compounds are formed. Benzene is oxidized quantitatively to phenol. Toluene is oxidized to o-cresol, m-xy-lene to l,3-xylen-4-ol, and naphthalene to f-naphthol. The addition of certain additional catalyst, such as molybdenum oxide, promoted coupling reactions and biphenyl was formed from benzene, bi- or poly-tolyl hydrocarbons from toluene, di- and polyxylyls from wi-xylene, and a... 

Methanol is prepared by the interaction of carbon monoxide and hydrogen, usually at 300-400°C and 275-360 atmospheres. A catalyst of zinc oxide promoted with chromic oxide is generally employed and conversions of about 15% per pass are usual. The methanol is condensed out and unreacted gases, with fresh make-up gas, recycled to the converters. In the second stage, methanol is oxidized to formaldehyde. In one process a mixture of methanol vapour and air is passed over a catalyst of molybdenum oxide promoted with iron at 350—450°C. The exit gases are scrubbed with water and the formaldehyde is isolated as an aqueous solution. 

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. 

Another SIMS study on model systems concerns molybdenum sulfide catalysts. The removal of sulfur from heavy oil fractions is carried out over molybdenum catalysts promoted with cobalt or nickel, in processes called hydrodesulfurization (HDS) [17]. Catalysts are prepared in the oxidic state but have to be sulfided in a mixture of H2S and H2 in order to be active. SIMS sensitively reveals the conversion of Mo03 into MoSi, in model systems of MoCf supported on a thin layer of Si02 [21]. 

Ruthenium on platinum was found to facilitate the oxidation of oCOad but noteoCOad interacting water, appeared to play a role of the oxygen source, replacing Pt-OH. Contrarily, tin and molybdates on platinum showed promoting effects for the oxidation of eoCOad but not AoCOad Redox couples of tin or molybdenum oxides appeared to play a role of a mediator as well as the ox en source. The active potentials were the bwest for molybdates and the second for tin. 

Acrolein and Acrylic Acid. Acrolein and acrylic acid are manufactured by the direct catalytic air oxidation of propylene. In a related process called ammoxida-tion, heterogeneous oxidation of propylene by oxygen in the presence of ammonia yields acrylonitrile (see Section 9.5.3). Similar catalysts based mainly on metal oxides of Mo and Sb are used in all three transformations. A wide array of single-phase systems such as bismuth molybdate or uranyl antimonate and multicomponent catalysts, such as iron oxide-antimony oxide or bismuth oxide-molybdenum oxide with other metal ions (Ce, Co, Ni), may be employed.939 The first commercial process to produce acrolein through the oxidation of propylene, however, was developed by Shell applying cuprous oxide on Si-C catalyst in the presence of I2 promoter. 

Molybdena catalysts have been with us for quite a long time. The term molybdena is used here to denote a composite catalyst consisting of molybdenum oxide supported on an activated support, commonly alumina. Early it was found that certain transition metals, notably cobalt and nickel, promote the molybdena catalyst for hydrodesulfurization (HDS) reactions. 

Although metals or even promoted metals have very low sulfur tolerances in synthesis reactions, other materials, such as metal oxides, nitrides, borides, and sulfides, may have greater tolerance to sulfur poisoning because of their potential ability to resist sulfidation (18). The extremely low steady-state activities of Co, Ni, and Ru metals in a sulfur-contaminated stream actually correspond to the activities of the sulfided metal surfaces. However, if more active sulfides could be found, their activity/selectivity properties would be presumably quite stable in a reducing, H2S-containing environment. This is, in fact, the basis for the recent development of sulfur active synthesis catalysts (211-215), which are reported to maintain stable activity/ selectivity properties in methanation and Fischer-Tropsch synthesis at H2S levels of 1% or greater. Happel and Hnatow (214), for example, reported in a recent patent that rare-earth and actinide-metal-promoted molybdenum oxide catalysts are reasonably active for methanation in the presence of 1-3% H2S. None of these patents, however, have reported intrinsic activities... 

The first polymerizations were free radical reactions. In 1933 researchers at ICI discovered that ethene polymerizes into a branched structure that is now known as low density polyethene (LDPE). In the mid- 50s a series of patents were issued for new processes in which solid catalysts were used to produce polyethene at relatively low pressures. The first was granted to scientists at Standard Oil (Indiana) who applied nickel oxide on activated carbon and molybdenum oxide on alumina. Their research did not lead to commercial processes. In the late 40s Hogan and Banks of Phillips were assigned to study the di- and trimerization of lower olefins. The objective was to produce high octane motor fuels. When they tried a chromium salt as promoter of a certain catalyst (Cr was a known reforming... 

The conventional nickel-based catalysts could be modified by adding oxide promoters such as potassium, lanthanam, cerium, and molybdenum in the catalyst formulations. It is believed that the added promoters improve the dispersion of nickel metal on the catalyst surface, thereby reducing the chance of carbon accumulation. Noble metals such as Pd, Pt, Ru, and Ir have been found to be more carbon tolerant as the solubility of carbon is less in these metals.54-57 However, they are more expensive than nickel-based catalyst, and as a consequence, they are less attractive for large-scale commercial applications. Alloying of nickel with other base metals such as Cu, Co, or noble metals such as Au, Pt, and Re has also been found to decrease... 

Ethylbenzene dehydrogenation is generally catalyzed by a potassium-promoted iron oxide catalyst. The most widely used catalysts are composed of iron oxide, potassium carbonate, and various metal oxide promoters. Examples of metal oxide promoters include chromium oxide, cerium oxide, molybdenum oxide, and vanadium oxide. " The potassium component substantially increases catalyst activity relative to an unpromoted iron oxide catalyst. Potassium has been shown to provide other benefits. In particular, it reduces the formation of carbonaceous deposits on the catalyst surface, which prolongs catalyst life. 

Gevaert and Jervis (63a) observed a 25% increase of activity for methanol oxidation on a tungsten oxide-molybdenum oxide catalyst irradiated to 1.2 x nvt with thermal neutrons. About 60% of the increase was annealed in 3 hours at 800°. This part of the increase was attributed to radiation damage, and the nonannealed part to promotion by the ca. 0.06% rhenium introduced by transmutation. Neither the kinetics nor the activation energy was changed appreeiably by the irradiation, but this may reflect an insensitivity of the reaction rather than an important observation about the centers introduced. Thus even... 

Commercial heterogeneous HDS catalysts for refinery use consist, almost without exception, of nickel- and/or cobalt-promoted molybdenum oxide located on a high surface area (approx. 300 m g ) alumina or silica-alumina support. Cobalt and nickel promoters increase the catalytic activity, particularly towards thiophenes whether Co or Ni is used as a promoter depends on the specific function for which the catalyst should be optimal. The catalyst material is shaped into porous pellets, a few millimeters in size, and these pellets are loaded into the reactor, forming a catalyst bed of 30-200 m volume. During start-up of a freshly loaded reactor, the catalyst bed, which is in the oxidic form, is sulfided, typically by treatment with an oil feed which has been spiked with a reactive sulfur compound that readily generates H2S in situ. The oxidic precursor phases (non-stoichiometric CoMo or NiMo surface oxides) are thereby converted into sulfidic phases termed Co-Mo-S and Ni-Mo-S. The conversion from the oxidic phase to the sulfidic is accompanied by a reduction in Mo oxidation state from +6 to +4. 

The term surface must be considered in a broad sense. If, for example, we are talking about an amorphous solid such as sihca gel, one understands immediately what is being considered as the surface, but when considering a lamellar solid, such as molybdenum oxide, both surfaces, that is, the external and internal (intrala-mellar) parts of the solid must be taken into accoimt. So, to promote intercalation is also to modify a surface, of course. 

In all studies, increase of Scat was observed with increasing temperature up to 673 K. It was stated by the Tokyo Group (T Kabe and colleagues) that the maximal Scat was approached at 473 K on the non-promoted molybdena, whereas the maximal uptake by Co- and Ni-promoted MoOx/Al20 was reached only at 573 K and 673K.[ d7] j. concluded that molybdenum oxide was preferably sulfided in the lower temperature interval, whereas higher temperatures were necessary for sulfiding nickel and cobalt species. 

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