Molybdenum catalysts reactions

Other processes recently reported in the Hterature are the gas-phase reaction of lactonitnle [78-97-7] with ammonia and oxygen in the presence of molybdenum catalyst (86), or the vapor-phase reaction of dimethyl malonate with ammonia in the presence of dehydration catalyst (87). 

Nicotinonitrile is produced by ammoxidation of alkylpyridines (11—24). A wide variety of different catalysts have been developed for this appHcation. For example, a recent patent describes a process ia which 3-methylpyridine is reacted over a molybdenum catalyst supported on siHca gel. The catalyst (PV Mo 20 ) was prepared from NH VO, H PO, and (NH Moy024. Reaction at 380°C at a residence time of 2.5 seconds gave 95% of nicotinonitrile at a 99% conversion (16). 

Research on catalytic coal Hquefaction was also carried out using an emulsified molybdenum catalyst added to the slurry medium to enhance rates of coal conversion to distiUate (26). Reaction at 460°C, 13.7 MPa (1980 psi) in the presence of the dispersed catalyst was sufficient to greatiy enhance conversion of a Pittsburgh No. 8 biturninous coal to hexane-soluble oils ... 

The reaction scheme is rather complex also in the case of the oxidation of o-xylene (41a, 87a), of the oxidative dehydrogenation of n-butenes over bismuth-molybdenum catalyst (87b), or of ethylbenzene on aluminum oxide catalysts (87c), in the hydrogenolysis of glucose (87d) over Ni-kieselguhr or of n-butane on a nickel on silica catalyst (87e), and in the hydrogenation of succinimide in isopropyl alcohol on Ni-Al2Oa catalyst (87f) or of acetophenone on Rh-Al203 catalyst (87g). Decomposition of n-and sec-butyl acetates on synthetic zeolites accompanied by the isomerization of the formed butenes has also been the subject of a kinetic study (87h). 

Gas-liquid fluidization is employed in the H-Oil process developed in the United States (H6). Cobalt-molybdenum catalyst particles of -in. diameter may be used at a reaction pressure of 100 atm or more and a temperature of about 400°C (V4). 

Diene 265, substituted by a bulky silyl ether to prevent cycloaddition before the metathesis process, produced in the presence of catalyst C the undesired furanophane 266 with a (Z) double bond as the sole reaction product in high yield. The same compound was obtained with Schrock s molybdenum catalyst B, while first-generation catalyst A led even under very high dilution only to an isomeric mixture of dimerized products. The (Z)-configured furanophane 266 after desilylation did not, in accordance with earlier observations, produce any TADA product. On the other hand, dienone 267 furnished the desired macrocycle (E)-268, though as minor component in a 2 1 isomeric mixture with (Z)-268. Alcohol 269 derived from E-268 then underwent the projected TADA reaction selectively to produce cycloadduct 270 (70% conversion) in a reversible process after 3 days. The final Lewis acid-mediated conversion to 272 however did not occur, delivering anhydrochatancin 271 instead. 

Similarly, a catalytic route to indigo was developed by Mitsui Toatsu Chemicals (Inoue et al, 1994) to replace the traditional process, which dates back to the nineteenth century (see earlier), and has a low atom efficiency/high E factor (Fig. 2.15). Indole is prepared by vapour-phase reaction of ethylene glycol with aniline in the presence of a supported silver catalyst. The indole is selectively oxidised to indigo with an alkyl hydroperoxide in the presence of a homogeneous molybdenum catalyst. 

The relative yields of 93, 94 and 95 in the molybdenum-catalyzed reactions turned out to be exceptionally sensitive towards catalyst concentration, with different characteristics for different reaction partners. For example, the following yields of 93, 94 and 95 b were obtained when oo-diazoacetophenone reacted with acrylonitrile in the presence of different amounts of Mo(CO)6 46, 2, 50% (0.2 mol-% catalyst) 68, 3, 28% (1 mol-%) 83, 4, 0% (15 mol-%). In contrast, the yield of cyclopropane... 

The formation of molybdenum complexes with diols (formed by olefin oxidation) was proved for the use of the molybdenum catalysts. Therefore, the participation of these complexes in the developed epoxidation reaction was assumed [242]. 

Triolefin A process for disproportionating propylene into a mixture of ethylene and 2-butene. The reaction takes place at 160°C over a cobalt/molybdenum catalyst on an alumina base. Developed by the Phillips Petroleum Company from 1963. A commercial plant was built by Gulf Oil Canada in 1966 and operated by Shawinigan between 1966 and 1972 before closing for economic reasons. 

Molybdenum catalysts that contain enantiomerically pure diolates are prime targets for asymmetric RCM (ARCM). Enantiomerically pure molybdenum catalysts have been prepared that contain a tartrate-based diolate [86], a binaph-tholate [87], or a diolate derived from a traris-1,2-disubstituted cyclopentane [89, 90], as mentioned in an earlier section. A catalyst that contains the diolate derived from a traris-1,2-disubstituted cyclopentane has been employed in an attempt to form cyclic alkenes asymmetrically via kinetic resolution (inter alia) of substrates A and B (Eqs. 45,46) where OR is acetate or a siloxide [89,90]. Reactions taken to -50% consumption yielded unreacted substrate that had an ee between 20% and 40%. When A (OR=acetate) was taken to 90% conversion, the ee of residual A was 84%. The relatively low enantioselectivity might be ascribed to the slow interconversion of syn and anti rotamers of the intermediates or to the relatively floppy nature of the diolate that forms a pseudo nine-membered ring containing the metal. 

Previously acrylonitrile had proved to be inert towards transition metal catalysed cross- and self-metathesis using ill-defined multicomponent catalysts [lib]. Using the molybdenum catalyst, however, acrylonitrile was successfully cross-metathesised with a range of alkyl-substituted alkenes in yields of40-90% (with the exception of 4-bromobut-l-ene, which gave a yield of 17.5%). A dinitrile product formed from self-metathesis of the acrylonitrile was not observed in any of the reactions and significant formation (>10%) of self-metathesis products of the second alkene was only observed in a couple of reactions. 

The success of the cross-metathesis reactions involving styrene and acrylonitrile led to an investigation into the reactivity of other Ji-substituted terminal alkenes [27]. Vinylboranes, enones, dienes, enynes and a,p-unsaturated esters were tested, but all of these substrates failed to undergo the desired cross-metathesis reaction using the molybdenum catalyst. 

It is interesting to note that the two reactions involving allyl acetate and the unprotected alcohol, but-3-en-l-ol, failed when the molybdenum catalyst was used. The failure of the Schrock catalyst to tolerate unprotected alcohols has also been observed in ring-closing metathesis [40], where a tertiary alcohol has proved to be the only success [41]. 

It appears that the molybdenum catalyst is more suited to the cross-metathesis of the sterically bulky vinylglycines. The cross-metathesis reaction of a similarly protected dehydro alanine gave only recovered starting material. 

Alkene cross-metathesis has also been recently used for the modification of silsesquioxanes and spherosilicates, by Feher and co-workers [46]. Reaction of vinylsilsesquioxane 28 with a variety of simple functionalised alkenes, in the presence of Schrock s molybdenum catalyst 3, gave complete conversion of the starting material and very good isolated yields of the desired products (75— 100%) (for example Eq. 28). 

Representative data illustrating the influence of Lewis base functional groups in the ADMET reaction are shown in Table 1. When molybdenum catalysts are used to polymerize ether or thioether dienes, little change in reaction rate is observed as compared with the standard, 1,9-decadiene, which possesses no heteroatoms in its structure. When a sulfur atom is three carbons atoms away from the alkene site, the reaction rate is reduced approximately one order of magnitude otherwise, the kinetics are all essentially unaffected [20a]. 

Mossbauer spectroscopy is one of the techniques that is relatively little used in catalysis. Nevertheless, it has yielded very useful information on a number of important catalysts, such as the iron catalyst for Fischer-Tropsch and ammonia synthesis, and the cobalt-molybdenum catalyst for hydrodesulfurization reactions. The technique is limited to those elements that exhibit the Mossbauer effect. Iron, tin, iridium, ruthenium, antimony, platinum and gold are the ones relevant for catalysis. Through the Mossbauer effect in iron, one can also obtain information on the state of cobalt. Mossbauer spectroscopy provides valuable information on oxidation states, magnetic fields, lattice symmetry and lattice vibrations. Several books on Mossbauer spectroscopy [1-3] and reviews on the application of the technique on catalysts [4—8] are available. 

Before the molybdenum catalysts can be used in hydrotreating reactions, they have to be sulfided. Raman spectroscopy sensitively reveals this transition. The characteristic Mo-S frequencies of MoS2 are at 389 and 411 cm-1 [45,46], much lower... 

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

The sulfidation mechanisms of cobalt- or nickel-promoted molybdenum catalysts are not yet known in the same detail as that of M0O3, but are not expected to be much different, as TPS patterns of Co-Mo/A1203 and Mo/Al203 are rather similar [56J. However, interactions of the promoter elements with the alumina support play an important role in the ease with which Ni and Co convert to the sulfidic state. We come back to this after we have discussed the active phase for the hydrodesulfurization reaction in more detail. 

The drawback of the CVD method is eliminated in ROMP, which is based on a catalytic (e.g., molybdenum carbene catalyst) reaction, occurring in rather mild conditions (Scheme 2.3). A living ROMP reaction ofp-cyclophanc 3 or bicyclooctadiene 5 results in soluble precursors of PPV, polymers 4 [31] and 6 [32], respectively, with rather low polydispersity. In spite of all cis (for 4) and cis and trans (for 6) configuration, these polymers can be converted into aW-trans PPV by moderate heating under acid-base catalysis. However, the film-forming properties of ROMP precursors are usually rather poor, resulting in poor uniformity of the PPV films. 

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