Molybdenum-activated carbon catalysts

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

Table V shows the results obtained for the carbonylation of dimethyl ether and methyl acetate with molybdenum catalysts supported on various carrier materials. In the case of dimethyl ether carbonylation, molybdenum-activated carbon catalyst gave methyl acetate with an yield of 5.2% which was about one-third of the activity of nickel-activated carbon catalyst. Silica gel- or y-alumina-supported catalyst gave little carbonylated product. Similar results were obtained in the carbonylation of methyl acetate. The carbonylation activity occured only when molybdenum was supported on activated carbon, and it was about half the activity of nickel-activated carbon catalyst.

Table V. Carbonylation Activities of Supported Molybdenum and Nickel-Activated Carbon Catalysts ...

In past years, metals in dilute sulfuric acid were used to produce the nascent hydrogen reductant (42). Today, the reducing agent is hydrogen in the presence of a catalyst. Nickel, preferably Raney nickel (34), chromium or molybdenum promoted nickel (43), or supported precious metals such as platinum or palladium (35,44) on activated carbon, or the oxides of these metals (36,45), are used as catalysts. Other catalysts have been suggested such as molybdenum and platinum sulfide (46,47), or a platinum—nithenium mixture (48). 

A mixed-valent polymolybdate on active carbon was prepared from molybdenum metal and H202, followed by the addition of active carbon to the aqueous solution [114,115], This catalyzed the epoxidation of several alkenes in 2-propanol using H202 as an oxidant, while the efficiency of H202 utilization was very low (< 25%). The epoxidation likely proceeded mainly on the surface of the catalyst because the recovered catalyst showed almost similar catalytic activity. 

Common catalyst compositions include oxides of chromium or molybdenum, or cobalt and nickel metals, supported on silica, alumina, titania, zirconia, or activated carbon. 

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... 

AUylic alkylations. This complex in combination with 2,2 -bipyridyl (bpy) catalyzes nucleophilic alkylation of allylic acetates and carbonates, but is less active than molybdenum or palladium catalysts. The displacement occurs with retention of configuration, as with Mo and Pd catalysts. However, alkylation occurs almost entirely at the more substituted end of the allylic group, regardless of the nucleophile. 

Feedstock Purification. In feedstock purification, mainly desulfurization, adsorption on active carbon was replaced by catalytic hydrogenation over cobalt-molybdenum or nickel-molybdenum catalyst, followed by absorption of the H2S on ZnO pellets with formation of ZnS. By itself this measure has no direct influence on the energy consumption but is a prerequisite for other energy saving measures, especially in reforming and shift conversion. 

The interest in adsorption of molybdenum stems primarily from its use as a carbon-supported catalyst [22]. The use of activated carbon for the removal of Mo-99 (used in nuclear medicine) has also been reported ] 158]. Only hexavalent Mo is stable under a wide pH range and in the absence of other complexing agents. At pH > 8, the dominant species is M0O4-, while at very low pH there is precipitation of the hydrated oxide between these two extremes polymeric anions are formed [123,159]. 

Replacing 0.10 atom of uranium with molybdenum stabilized the catalyst with only a small effect on activity and acrylonitrile selectivity (Table VI). Further replacement of uranium by molybdenum markedly reduced catalyst activity, so that contact time had to be increased to maintain a high conversion. The addition of molybdenum resulted in a greater production of by-product HCN and correspondingly less carbon oxides (Table VII). A similar effect was obtained with vanadium. However, the vanadium seemed to increase activity as well as stabilize the catalyst. 

Several other methods have been employed for the preparation of carbon-supported catalysts, although to a lesser extent that impregnation methods. Nakamura et al. [38] prepared molybdenum catalysts for ethene homologation by physical deposition of gaseous [Mo(CO)6]. Their supports were commercial activated carbons that were subjected to different treatments to modify then-surface. The authors compared these supports with oxidic supports and concluded that the interaction between the metal carbonyl and the carbon supports were weaker. Furthermore, they observed that oxidation of the carbon surface was effective in enhancing the catalytic activity of Mo/C, and they ascribed this effect to the contribution of the surface oxygen groups to the partial oxidation of decomposed [Mo(CO)6]. 

Work by Prins, de Beer, and co-workers represents a great contribution to our knowledge of the structure of carbon-supported hydrotreating catalysts as well as of the kinetics and mechanisms of these reactions. These authors first reported that the activity of carbon-supported molybdenum and tungsten catalysts was higher than that of their counterparts supported on alumina or silica [80,81]. They... 

A significant development for the selective synthesis of alkenes makes use of alkene metathesis. Metathesis, as applied to two alkenes, refers to the transposition of the alkene carbon atoms, such that two new alkenes are formed (2.110). The reaction is catalysed by various transition-metal alkylidene (carbene) complexes, particularly those based on ruthenium or molybdenum. The ruthenium catalyst 84, developed by Grubbs, is the most popular, being more stable and more tolerant of many functional groups (although less reactive) than the Schrock molybdenum catalyst 85. More recently, ruthenium complexes such as 86, which have similar stability and resistance to oxygen and moisture as complex 84, have been found to be highly active metathesis catalysts. 

By this time we were doing about as well as had been done previously with a molybdenum oxide alumina catalyst, but with considerably less carbon formation. So now things became more serious, but not serious enough to get people very excited about it. After all, we had been using a 3% platinum on silica catalyst, and even in those days 3% platinum was pretty expensive. Platinum on silica-alumina did much better with respect to octane number but we could not control the hydrocracking very well, so we switched to alumina which had an intermediate activity. The results looked pretty good, particularly because we could run for days without much loss in activity. 

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