Molybdenum oxides, deposition

Iron-iron oxide catalysts have been repeatedly reported to lie unsatisfactory for methanol decomposition or oxidation, because of their activity in causing complete oxidation to carbon dioxide or decomposition to carbon if a deficiency of oxygen prevails. However, catalysts composed of iron and molybdenum oxide have been found to be very efficient for methanol oxidation.21 Such a mixed catalyst apparently combines the excellent directive power of molybdenum and the activity of iron. Molybdenum oxide deposited on small iron balls was shown to be 100 per cent efficient... 

On the other hand, Scheller 110 goes to great length to obtain acetylene in a pure condition for reaction with steam at a temperature of 600° C. over a catalyst composed of molybdenum oxide deposited on asbestos. Despite the high temperature used a yield of 17 per cent of acetaldehyde is claimed. This may in part be attributed to the high proportion of steam used, i.e., 400 volumes steairi to IS volumes acetylene. With a 35 cm. length of catalyst a rate of one liter of this mixture per minute per sq. cm. of cross section is used. 

The benzene concentration in the feed mixture with air must be set outside the flammability limits, which are 1.4 and 7.1 per cent volume at 25 C. Operations are conducted below the lower limit at 1.2 to 1.3 per cent volume. The catalyst, placed in a fixed bed, consists of vanadium pentoxide and molybdenum oxide, deposited on a low... 

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). 

Photoreduction of Si02 doped by six valance molybdenum results in decrease of the surface concentration of Mo ions and, as a consequence, reduces the capability of the sample to emit 2. However, such a treatment does not lead to a complete suppression of emission capability because, according to [96], illumination reduces only 30% of Mo ions in molybdenum oxide catalysts deposited on Si02. 

These chemical reactions possibly precede the electrochemical reactions. Thus the electrochemical reactions in the case of molybdenum oxides may be taken to be similar to those which occur in electrorefining, i.e., electrochemical dissolution of molybdenum from the impure metallic molybdenum anode and subsequent deposition at the cathode. The combination of the chemical and the electrochemical reactions occurring at the anode can be represented in the following way ... 

It is now clear that, when propagation centers are formed, olefin polymerization by all solid catalysts (including the Phillips Petroleum catalyst from chromium deposited on oxides, and the Standard Oil catalyst of molybdenum oxide on aluminum oxide) essentially follows the same mechanism chain growth through monomer insertion into the transition-metal-carbon bond, with precoordination of the monomer. Interestingly,... 

The pH value of the impregnation solutions for depositing the active elements on alumina is an important variable in catalyst preparation. For example, Jian and Prins (66) reported that the content of bulk molybdenum oxide (detected by XRD) increases in MoP/Al catalysts when the pH of the impregnation solution decreases from 9 to 1 as a result of addition of phosphorus (Fig. 27). 

An explanation may be given by taking into account the images and analyses (Fig. 9.17C and D) obtained on the sample from the edge of the extruded elements. A specific morphol-ogy, spheroidal particles of approximately 0.1 pm in diameter, is linked to the detection of a significant concentration of Mo. It has, in this case, been possible to incriminate the control of the impregnation process, with the molybdenum oxide being deposited in the porosity on the surface of the extruded elements. 

The initial heavy deposits of coke almost certainly originate mainly from asphaltenes in the feed. Preferential adsorption of asphaltene fractions have been observed on cobalt and molybdenum oxides [23] and sulphides [24] as well as on sulphided nickel-molybdenum... 

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. 

Comparing results of molybdenum electro-deposition from several types of electrolytes, it was confirmed that the process is most successful in electrolytes consisting of a mixture of alkali metal fluorides and boron oxide (or alkali metal borate), to which molybdenum oxide or alkali metal molybdate is added as the electrochemical active component. 

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... 

Hydroxybenzonitrile can be synthesized directly from p-cresol over the bismuth-molybdenum oxide, iron-antimony oxide or uranium-antimony oxide catalysts [81] normally used for the ammoxidation of propylene, although the catalysts are rapidly deactivated by coke-like deposits [81]. 

Molybdenum oxide films prepared by sublimation in vacuo on to a glass wall are converted into an active catalyst for propene metathesis at 0.4 kPa and 20°C by treatment of the surface with ethene (or propene) and atomic hydrogen at — 196°C (Kazuta 1987). Active sites can also be obtained by exposing the molybdenum oxide film to CH2 radicals produced by the reaction of CH2I2 with A1 or Mg metals deposited near the oxide film (Kazuta 1988, 1990). 

A diffuse reflectance measurement begins with the collection of a reference scan. For samples deposited on reflective substrates, such as metallic molybdenum, the bare metal serves as a reference to account for any absorption in the metal itself. Samples deposited onto transparent substrates, such as a transparent conducting oxide deposited on glass (e.g., indium-tin oxide, or ITO), require the use of a white diffuse reflectance standard. This standard is often made from Ba2S04 or PTFE based material similar to, if not the same as, that used to coat the interior surface of the integrating sphere. The user places the standard against the open... 

The formation of mixed metal Mo-Co oxide HDS catalysts on the MCM support occurs in a sequential reaction by first depositing the molybdenum oxide followed by pyrolysis of GolCOlsNO to disperse the Co over the Mo-covered support.The option of co-sonicating the molybdenum carbonyl and cobalt carbonyl nitrosyl concurrently yields catalysts with poorly reproducible stoichiometries. The resulting catalyst (13 wt.% CoO and 43 wt.% M0O3) was examined as an HDS catalyst for dibenzothiophene, and was found to display 1.7 times greater activity than a commercial Co-Mo-Al catalyst. 

A different interpretation of the role played by the different molybdenum oxide species deposited on the surface of silica was proposed for the oxidation of CH4 into HCHO. Thus, Suzuki et al. [125] concluded that well-dispersed molybdenum oxide clusters on the silica surface are the active species for the reaction. By contrast, Ozkan and coworkers [126,127] proposed that the Mo=0 sites present in the M0O3 crystals are catalytically active while Mo-O-Mo bonds accelerate the deep oxidation of methane. However, the reactivity of supported molybdenum oxide differs from bulk M0O3, and no direct extrapolation can be made [103]. 

---