Molybdenum promoter

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). 

Molybdenum-promoted cyclodimerization of cyclooctatetraene262 and its cocyclization with alkynes263,2633 also appear to proceed via three- and five-membered molybdenacycles followed by further cyclization reactions that may or may not involve promotion by Mo (Scheme 56). 

Contrary to the literature (ref. 4), molybdenum promotion did not bring to a rise in the specific activity of the catalyst in our reaction conditions. In fact there were decreases in the specific reaction rates. Adding high level of molybdenum (x = 0.4) made the rate drop considerably. However the activity of the molybdenum promoted catalysts was found proportional to their metallic surface area. Moreover, it was shown (ref. 13) that this metallic surface area was a direct function of the phase content in the alloy (Mo-doped Ni A13 with a low Mo content 0.2 at %). The agglomerates issued from P seem to be the only active phase in the hydrogenation of valeronitrile. This explains why all Mo-promoted catalysts had the same intrinsic activity but also why increasing the Mo promoter level did not affect the selectivity. 

For the sequence A — B — C, the ratios kjb bg in 2-propanol Table 3. do not differ significantly from the ratios k /kgbg in cyclohexane, this result holds for pure nickel and molybdenum promoted catalysts. Taking into account that the initial hydrogenation rate which is proportional to k b is notably enhanced in 2-propanol, one can assume that the rate of hydrogenation of citronellal to citronellol increases in similar proportion. 

Similarly 2-propanol exalts the selectivity in citronellol for the sequence B — C — E, from the values of the ratios k bg/k bj., it appears that the maximum yield in citronellol over pure nickel rises from 59% to 91%. Over molybdenum promoted catalysts the selectivity of this step increases with che molybdenum composition in the oulk to reach 100% with NiMOq 1g, i.e. citronellol is not hydrogenated to 3,7dimethyloctanol. 

The catalytic activity of Fe carbides, molybdenum oxynitride and oxycarbide has been evaluated for coal liquefaction and heteroatom removal of model compounds related to coal. Preliminary results show that the LP nanoparticles are active catalysts for coal liquefaction. In fact, they are more active for heteroatom removal than a molybdenum promoted sulfated hematite, even though surface characterization indicates that as introduced into the reactor they exhibit surface oxidation. 

An ESCA analysis of the molybdenum promoted Raney nickel showed that when a low molybdenum content alloy was used, the activated catalyst had greater amounts of nickel on the surface than the unpromoted active catalyst. At a 2% molybdenum content the nickel surface area in the activated catalyst reached a maximum and then decreased with the presence of more molybdenum. These findings correlate with the observed maximum in catalytic activity observed with the 2% molybdenum Raney nickel catalyst. The initial increase in... 

Hydrogenation experiments with simultaneous acoustic irradiation were carried out by using iso-propanol (2-propanol) as solvent in an automatic laboratory-scale autoclave (Parr 4560) with an effective liquid volume of 250 ml. The operating conditions were as follows 50 bar hydrogen pressure and 70°C (343 K) as the reaction temperature. The catalyst-to-citral ratio was 1 25 (wt wt) in the beginning of the reaction. A commercial molybdenum promoted Raney nickel catalyst with a mean particle size of approx. 22 pm and the specific surface area in the range of 80 m /g was used in the experiments. The reactor contents were analyzed oiF-line with gas chromatography (GC). 

Cu rich alloys having high strength and high electrical conductivity, and age-hardenable Fe rich alloys can be developed through consideration of the Cu-Fe-Mo phase diagram. Molybdenum is added to steels traditionally in order to improve their mechanical properties, in particular ductility, since molybdenum promotes grain refinement. The additions of copper to steels increase their corrosion resistance and improve formability. 

The preparation of D-mannitol from standard monosaccharides and the processing of hardwoods for producing xylitol and other polyols and monosaccharides have been reviewed. The hydrogenation of xylose to xylitol over a molybdenum-promoted copper catalyst and... 

Finally, of interest to workers in catalytic processes using carbonyl clusters, some work on CO hydrogenation catalysts derived from metal carbonyl clusters (ie molybdenum promoted Rh/Si02 and Rh/Zr02) has been published . 

N2O in the feed, about 2% of the molybdenum on the surface is present as Mo + after the catalytic reaction. On the contrary, in the absence of N2O, no reduced molybdenum was observed. When N2O is added, hydroxyls decrease and the bonds corresponding to M=0 increase further. This effect is more marked when the amount of N2O introduced is higher. In the presence of O2 only, the number of M=0 bonds formed increases further. Molybdenum is in a higher oxidation state in the presence of O2. On the contrary, when N2O is added. Mo is less oxidized. N2O inhibits the oxidation of molybdenum, promoting its reduction. N2O could be adsorbed in the same vacancies where O2 adsorption usually occurs. The inhibition in the adsorption of O2 can have as a consequence, to limit (or inhibit) the formation of more electrophilic oxygen species (as 0 , O2), formed from the dissociation of molecular oxygen. These species could promote the non-selective attack of the hydrocarbons. A higher amount of N2O deeply reduces the catalysts and promotes the formation of (reduced) sites where carbonaceous products could be formed. ... 

Steam mole ratio as low as 3 1, while catalysts containing mixed chromium, ceria, and molybdenum promoters, togetlier with potash, were more selective but had to be operated at steam ratios of about 7 1 ... 

Dahl and coworkers [116] reported molybdenum-promoted nitrosyl bond activation leading to the formation of nitrido and/or imido hgand-containing metal clusters. A solution of Mo2(r/ -C5Me5)2(CO)4 and Co(CO)3(NO) in tetrahydro-furan, upon photolysis under a slow stream of N2, gives ( / -C5Me5)3M03C02-(CO)8(/t3-NH)(/t4-N). 

---