Molybdenum showing decomposition

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

Impurities with catalytic effects—Impurities that act as catalysts, reducing the activation energy of a process, may increase the rate of reaction significantly, even when present in small quantities. The presence of sulfuric acid, for example, increases the rate of decomposition and decreases the observed onset temperature of various isomers of ni-trobenzoic acid [28]. Also, other substances such as NaCl, FeCl3, platinum, vanadium chloride, and molybdenum chloride show catalytic effects. As a result, the decomposition temperature can be lowered as much as 100°C. Catalysts, such as rust, may also be present inadvertently. Some decomposition reactions are autocatalyzed, which means that one of more of the decomposition products will accelerate the decomposition rate of the original substance. 

Tricarbonyltris(pyridine)molybdenum(0) is a yellow to orange crystalline compound that can be handled in the ambient atmosphere without noticeable decomposition. It can be stored indefinitely at 0-5°C under an inert atmosphere. It decomposes at 205-210°C (a gradual change in color from yellow to brown is already observed starting at 100-105°C). Its IR spectrum shows two carbonyl bands at 1901 and 1764 cm. ... 

Oxidation of trans-[Mo(N2)2(dppe)2] with I2 in methanol allows isolation of the unstable cationic complex frans-[Mo(N2)2(dppe)2]I3.6 This cation has also been prepared electrochemi-cally and the rate of its decomposition by loss of N2 studied.6 A range of dinitrogen complexes shows reversible one-electron oxidation in solution, but in general the monocations are too unstable to be isolated for molybdenum.6... 

The fact that the epoxide yield decreases at higher temperatures, longer reaction time, higher catalyst concentration, and lower olefin concentration may be caused by two possible side reactions—decomposition of the hydroperoxide and addition of the alcohol to the epoxide. Initial kinetic studies of the decomposition of tert-butyl hydroperoxide in the presence of molybdenum hexacarbonyl showed second-order dependence on hydroperoxide and first-order dependence on catalyst concentration. These results indicate that the decomposition of hydroperoxide is caused by the reaction between the hydroperoxide-metal complex and another molecule of hydroperoxide. With higher temperature, higher... 

Metals with low oxidation potentials and high Lewis acidity in their highest oxidation states are superior catalysts and show the following order of reactivity Mo > W > V > Ti. Metals which readily promote homolytic decomposition of alkyl hydroperoxides via one-electron pathways, e.g., Co, Mn, Fe, and Cu, are not effective. Certain main group elements, e.g., B and Sn, exhibit activity, albeit significantly lower than molybdenum. 

In the absence of molybdenum, the blank dehydrated zeolites showed no CO hydrogenation activity even up to 400°C. In contrast, measurable quantities of aliphatic hydrocarbons were detected over the molybdenum-zeolite catalysts at 300°C and above. Figs. 1-2 show the time dependence of CO conversion over MOii g HY and Mo g CsY at 300°C. The conversion and product distribution were dependent on the reaction conditions, a typical set of results is illustrated in Table 1. The molybdenum-zeolites prepared by adsorption and decomposition of Mo(C0)g resembled closely the alumina-supported molybdenum catalysts prepared by decomposing Mo(C0)g on alumina (ref. 13). The results obtained presently could not match the figures reported by Brenner et aK (ref. 8), but this could be due to the significant differences in the reaction conditions used by the above authors. However, a comparison with the silica-molybdena catalyst (prepared by impregnation of ammonium molybdate) clearly indicates that the molybdenum-zeolites were more active on per molybdenum basis. The improved activity is due to the presence of zerovalent molybdenum (for LaY and HY, residual zerovalent molybdenum were responsible for the activity). 

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