Molybdenum catalysts for

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. 

Hoveyda and co-workers have developed chiral catalysts for asymmetric alkene metathesis. They have demonstrated that with their chiral molybdenum catalyst asymmetric syntheses of dihydrofurans through catalytic kinetic resolution by RCM and enantioselective desymmetrization by RCM are feasible processes (Scheme 40) <1998JA9720>. The use of Schrock s molybdenum catalysts for asymmetric alkene metathesis has been reviewed <2001CEJ945>. 

Heterocycles as ligands in molybdenum catalysts for asymmetric allylic alkylat-ions 04ACR159. 

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]. 

Table 2.3 Examples of supported molybdenum catalysts for metathesis reactions"...

Scheme 25. Monomers and Single-Site Molybdenum Catalysts for Stereoselective ROMP...

More recently, the pincer iridium catalysts for alkane dehydrogenation, in combination with Schrock s molybdenum catalyst for olefin metathesis (Chapter 21), has been shown to catalyze alkane metathesis (Equation 18.47). This combination of catalysts provides... 

Applications of molybdenum-based catalysts for CO-H2 reactions have received much attention since workers at the U.S. Bureau of Mines (111) reported high rates of molybdenum catalysts for methanation, exceeded only by those of the most active group 8 metal catalysts (Fe, Co, Ni, and Ru). Moreover, they were relatively resistant to sulfur poisoning and could simultaneously catalyze the water gas shift reactions during hydrocarbon synthesis, thus allowing a CO-rich gas mixture to be used. Recently, studies have been extended to various molybdenum compounds and supported catalysts (45,49,106,112). The turnover rates based on CO chemisorption for supported and unsupported molybdenum carbides (0.04-0.131 s ) were higher than for corresponding Mo metal (0.02 s ) at 570 K and atmospheric pressure (95,113). Oxides, sulfides, and nitrides of molybdenum were reported to exhibit somewhat lower turnover rates than metal or carbide counterparts (112). These values are comparable to those of Ru (0.03-0.77 s ), Ni (0.066 s ), and Co (0.09 s ), which are known as the most active catalysts for these reactions (114). 

Guinel MJF, Bonakdarpour A, Wang B, Babu PK, Ernst F, Ramaswamy N, Mukerjee S, Wieckowski A (2009) Carbon-supported, selenium-modified ruthenium - molybdenum catalysts for oxygen reduction in acidic media ChemSusChem 2 658-664... 

Most of the research performed on olefin metathesis in ILs has been done with Ru-based catalysts although the very first olefin metathesis in ILs was reported in 1995 with a tungsten catalyst [30], In 2000, Bayer AG patented the use of Ru and molybdenum catalysts for olefin metathesis in ILs [31]. 

The effect of chemisorption on both the short- and the long-term mechanical strength of dispersed porous structures was investigated in detail using a cobalt-molybdenum catalyst for propylene oxidation as the model system. These results are presented in Figure 7.59, showing the durability as a function of the stress applied. The durability is defined as the logarithm of the time to fracture under a constant applied load. 

The use of molybdenum catalysts for allylic alkylation has been reported, and can be considered as complementary to the palladium-catalysed reactions. ... 

More complex heterocyclic structures have been synthesized efficiently and with high stereoselectivities using tandem AROM-RCM sequences [85] similarly, application of tandem AROM/CM to functionalized norbomenes affords enantio-pure highly functionalized cydopentanes [86]. A polymer-supported chiral molybdenum catalyst for enantioselective metathesis effidendy promotes ARCM (kinetic resolution as well as desymmetrization) and AROM reactions and can be recycled [87]. 

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