Molybdenum catalysts, silica-supported

Olefin metathesis is the transition-metal-catalyzed inter- or intramolecular exchange of alkylidene units of alkenes. The metathesis of propene is the most simple example in the presence of a suitable catalyst, an equilibrium mixture of ethene, 2-butene, and unreacted propene is obtained (Eq. 1). This example illustrates one of the most important features of olefin metathesis its reversibility. The metathesis of propene was the first technical process exploiting the olefin metathesis reaction. It is known as the Phillips triolefin process and was run from 1966 till 1972 for the production of 2-butene (feedstock propene) and from 1985 for the production of propene (feedstock ethene and 2-butene, which is nowadays obtained by dimerization of ethene). Typical catalysts are oxides of tungsten, molybdenum or rhenium supported on silica or alumina [ 1 ]. 

SMPO [styrene monomer propylene oxide] A process for making propylene oxide by the catalytic epoxidation of propylene. The catalyst contains a compound of vanadium, tungsten, molybdenum, or titanium on a silica support. Developed by Shell and operated in The Netherlands since 1978. 

Two spectra of sulfided catalysts in Fig. 4.16 show that sulfur can also be detected, albeit with lower sensitivity, because of the Z2 dependence of the cross section in (4-6). Figure 4.17 gives the S/Mo atomic ratio as a function of sulfidation temperature. It indicates that sulfur uptake by M0O3 is already significant at room temperature and increases to the expected S/Mo ratio of 2 above 100 °C. Combination of these results with SIMS and XPS data have led to a detailed mechanism for the sulfidation of silica-supported molybdenum catalysts [21] (see also Chapter 9). 

The newest and most commercially successful process involves vapor phase oxidation of propylene to AA followed by esterification to the acrylate of your choice. Chemical grade propylene (90—95% purity) is premixed with steam and oxygen and then reacted at 650—700°F and 60—70 psi over a molybdate-cobait or nickel metal oxide catalyst on a silica support to give acrolein (CH2=CH-CHO), an intermediate oxidation product on the way to AA. Other catalysts based on cobalt-molybdenum vanadium oxides are sometimes used for the acrolein oxidation step. 

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.

BANARES AND FIERRO Silica-Supported Molybdenum(VI) Catalysts 357... 

In catalytic toluene hydrodealkylation, toluene is mixed with a hydrogen stream and passed through a vessel packed with a catalyst, usually supported chromium or molybdenum oxides, platinum or platinum oxides, on silica or alumina. (50). The operating temperatures range from 500—595°C... 

In both fresh and regenerated catalysts, the MCM-41 supported catalysts are better than amorphous silica supported ones. Physically mixed molybdenum oxide catalysts with Def-MCM41 support are particularly active. The steady state activity decreases in the order Mo/DM > Mo/M > Mo/Si02. Interestingly, the rate of deactivation also seems to depend on... 

IR spectroscopy shows that CO adsorption on Mo3N/y-Al203 catalysts gives vCO bands at 2045 and 2200 cm 1 due to linearly-adsorbed CO on Mo and N sites respectively.97 Similar data for CO on MoP/y-Al203 includes vCO at 2037 cm 1 from linearly-coordinated CO,98 while for CO adsorption on silica-supported Mo2C catalysts they are at 2089 and 2032 cm-1.99 CO adsorption on silica-supported molybdenum forms a Mo(II) carbonyl, with vCO near 2170 cm-1.100... 

ACTIVE SPECIES AND MECHANISM FOR MIXED ALCOHOL SYNTHESIS OVER SILICA-SUPPORTED MOLYBDENUM CATALYSTS... 

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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