Carbon monoxide molybdenum

In a vacuum, uncoated molybdenum metal has an unlimited life at high temperatures. This is also tme under the vacuum-like conditions of outer space. Pure hydrogen, argon, and hehum atmospheres are completely inert to molybdenum at all temperatures, whereas water vapor, sulfur dioxide, and nitrous and nitric oxides have an oxidizing action at elevated temperatures. Molybdenum is relatively inert to carbon dioxide, ammonia, and nitrogen atmospheres up to about 1100°C a superficial nitride film may be formed at higher temperatures in the latter two gases. Hydrocarbons and carbon monoxide may carburize molybdenum at temperatures above 1100°C. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

Catalysts in an oxidized state showed high activity in the oxidation of carbon monoxide [nickel catalysts (146) ] and hydrogen [molybdenum catalysts (146a)]. 

Scheme 6.46 Palladium-catalyzed aminocarbonylations using molybdenum hexacarbonyl as a solid source of carbon monoxide.

In a more recent study, Wannberg and Larhed reported solid-supported aminocar-bonylations employing molybdenum hexacarbonyl as a solid source of carbon monoxide [37]. Carbon monoxide is smoothly liberated at the reaction temperature upon the addition of the strong base l,8-diazabicyclo[2.2.2]octane (DBU). In this transfor-... 

A set of aryl halides was reacted with carbonyl hydrazides and molybdenum hexacar-bonyl [Mo(CO)6] as a source of carbon monoxide, employing fluorous triphenylphos-phine (F-TPP) as ligand and the perfluorocarbon liquid FC-84 as a perfluorinated solvent (Scheme 7.87 see also Scheme 6.46c). 

The molybdenum hexacarbonyl complex was recently introduced as a condensed source of carbon monoxide for Heck carbonylations [29]. This easily handled and inexpensive solid delivers a fixed amount of carbon monoxide when heated to approxi-... 

A conmercial catalyst frcm Harshaw was used, a 3 1 mixture of molybdenum trioxide and ferric molybdate, as well as the two separate phases. Kinetic experiments were done previously in a differential reactor with external recycle using these same catalysts as well as several other preparations of molybdenun trioxide, including supported samples. Hie steady state kinetic experiments were done in the temperature range 180-300 C, and besides formaldehyde, the following products were observed, dimethylether, dimethoxymethane, methyl formate, and carbon-monoxide. Usually very little carbon dioxide was obtained, and under certain conditions, hydrogen and methane can be produced. 

In a noteworthy series of studies, Herndon has shown that cyclopropylcarbenes can be used as four-carbon components in molybdenum- and tungsten-mediated [4 + 2 + l]-reactions with alkynes and carbon monoxide (CO). These reactions give cycloheptadienones in moderate yields and with moderate selectivity (Equations (26)—(28)). The mechanism of this reaction is proposed to proceed through a series of steps involving metathesis, GO insertion, ketene formation, cyclopropane cleavage, and finally reductive elimination (Scheme 43).133... 

The fact that surface structure, in particular steps and coordinatively unsaturated sites, has an influence on the state and reactivity of carbon monoxide is entirely in keeping with the empirical correlation (Fig. 6) between heat of adsorption, electron binding energies, and molecular state. Elegant studies by Mason, Somorjai, and their colleagues (32, 33) have established that with Pt(lll) surfaces, dissociation occurs at the step sites only, and once these are filled carbon monoxide is adsorbed molecularly (Fig. 7). The implications of the facile dissociation of carbon monoxide by such metals as iron, molybdenum, and tungsten for the conversion of carbon monoxide into hydrocarbons (the Fischer-Tropsch process) have been emphasized and discussed by a number of people (32,34). 

Sulfur and carbon monoxide can be killers (literally) with hydrogenation catalysts. It will poison them, making them completely ineffective. Some sulfur often shows up in the benzene feed, carbon monoxide in the hydrogen feed. The alternatives to protect the catalyst are either to pretreat the feed and/or the hydrogen or to use a sulfur resistant catalyst metal like tin, titanium, or molybdenum. The economic trade-offs are additional processing facilities and operating costs vs. catalyst expense, activity, and replacement frequency. The downtime consequences of catalyst replacement usually warrarit the more expensive treatment facilities. 

Finely divided molybdenum reacts with carbon monoxide under pressure to form molybdenum hexacarbonyl ... 

However, when heated with carbon monoxide at temperatures above 1,000°C, no carbonyl is obtained but a thin film of molybdenum carbide forms over the metal. 

Molybdenum hexacarbonyl usually is made by treating molybdenum pen-tachloride with zinc dust in carbon monoxide under high pressure (90 to 120 atm). Also, it can be prepared by direct combination of molybdenum metal powder with carbon monoxide under pressure. 

Thermal dissociation of molybdenum hexacarbonyl yields molybdenum metal and carbon monoxide. 

Molybdenum hexacarbonyl is toxic by ingestion, inhalation and other routes of exposure. It decomposes, giving toxic carbon monoxide. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

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