Nickel-molybdenum catalysts, effect

A favorable combination of valence forces of both components seems to be the basic principle of the nickel-molybdenum ammonia catalyst. It has been found (50) that an effective catalyst of this type requires the presence of two solid phases consisting of molybdenum and nickel on the one hand and an excess of metallic molybdenum on the other. Similar conditions prevail for molybdenum-cobalt and for molybdenum-iron catalysts their effectiveness depends on an excess of free metal, molybdenum for the molybdenum-cobalt combination and iron for the molybdenum-iron combination, beyond the amounts of the two components which combine with each other. A simple explanation for the working mechanism of such catalysts is that at the boundary lines between the two phases, an activation takes place. In the case of the nickel-molybdenum catalyst, the nickel-molybdenum phase will probably act preferentially on the hydrogen and the molybdenum phase on the nitrogen. 

The effectiveness of catalysts A and B to desulfurize SRN and blend naphtha was investigated and the results are shown in Table 4. Figure 4, which shows the performance of catalyst A, illustrates that it is easier to desulfurize SRN than blend naphtha. The results also confirmed higher HDS performance with blend naphtha than SRN with both catalysts. This could be due to the refractive material in the hydrocracked fraction of the blend naphtha. With blend naphtha and catalyst A the minimum total sulfur ofO.69 ppm was obtained at 320°C, while with SRN the minimum was 0.37 ppm at 300°C. Above these temperatures, the occurrence of H2S-alkene recombination reactions increased the total sulfur. Nickel-molybdenum catalysts are known to reduce recombination reactions by hydrogenating alkenes. Higher temperatures and very active catalysts can cause cracking at the reactor outlet allowing alkenes production[13],... 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

IR spectra, 27 283, 284 magnetic measurements, 27 280 oxidized state, 27 289 Raman spectra, 27 284 reduced state, 27 291 reflectance spectroscopy, 27 279 X-ray diffraction, 27 272, 273 support interactions, 27 290 Cobalt monoxide, field effect, 27 44, 45 Cobalt(nickel)-molybdenum-sulfide catalysts, 42 417... 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

The catalyst was 100 ml of American Cyanamid HDS-3A, a 1/16-inch diameter extrudate of nickel-molybdenum-alumina. It was diluted with inert, granular alpha-alumina to provide a bed depth of 18 inches in the middle section of a 0.96-inch ID vertical reactor with a 5/16-inch OD internal thermocouple well. The catalyst was progressively more dilute toward the top of the bed to minimize exothermic temperature effects, and end sections were packed with alpha-alumina to provide for preheat and cooling zones. 

Catalysts help customers comply cost-effectively with clean-air regulations. Hydrocarbons, carbon monoxide, and nitrogen oxides can be removed using supported precious metal catalysts. Organic sulfur compounds are converted to H2S using nickel/molybdenum or cobalt/molyb-denum on alumina catalysts. Sulfur can be recovered in a Claus process unit. The Claus catalytic converter is the heart of a sulfur recovery plant. 

J.F. Kriz, J. Monnier, and M. Ternan, Nickel - molybdenum - alumina catalysts Effects of doping with fluoride and lithium and changes in particulate size when applied to bitumen hydroproceasing, Preprints, llth Can. Symp. Catal 11 (1990) 201 210 ... 

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

In 1959, H. Beuther et al. (8) of Gulf Oil Company published the first systematic study of the HDS activity of CoMo and NiMo supported on alumina as a function of the atomic ratio Co(Ni)/Mo. As a result, they showed what they called a promoter effect of the cobalt (or nickel) on the molybdenum for atomic ratios Co/Mo = 0.3 and Ni/Mo = 0.6. This publication was preceded by several patents proposing similar atomic ratios for cobalt by Union Oil of California (1948) (9) and Shell Oil Company (1954) (10) and for nickel by Union Oil of California (1954)(/7). Figure 1 shows a typical activity curve of NiMo/Al203 catalysts as a function of the value of the atomic ratio Ni/Mo (12). 

To promote the activity and selectivity of Raney nickel catalysts, alloying of the starting Ni-Al alloy with metal was often used. For instance, Montgomery (ref. 4) prepared catalysts by activating ternary alloy powders of Al (58 wt %)-Ni (37-42 wt %) - M (0.5 wt %) where M = Co, Cr, Cu, Fe and Mo. All promoted catalysts tested were more active than the reference catalyst, in hydrogenation of butyronitrile. Molybdenum was the most effective promoter. With Cr or Ti, hydrogenation of isophtalonitrile on Raney nickel occurred at lower optimum temperature than with non activated nickel (ref. 5). It was shown that addition of Ti or Co to Raney nickel suppressed the formation of secondary amine (ref. 6). 

The modification of the Raney nickel with low Mo amount (x = 0.05 or 0.1) lead to catalysts which had roughly the same kinetic behaviour as the undoped. Further introduction of molybdenum in the Ni A13 alloy had a substantial negative effect on the properties of the catalysts, with a drop in the... 

The modification of the Ni Al alloy by addition of molybdenum or chromium has a significant effect on the properties of the Raney nickel catalyst in the reaction of hydrogenation of valeronitrile. In the case of molybdenum, the catalytic properties may be correlated to the physico-chemical characteristics of the catalysts. Chromium is an effective promoter for initial activity and for selectivity. The mechanism for promotion of chromium in Raney nickel is not known exactly. 

The solvents used to eliminate sodium iodide after co-reduction of the mixtures of nickel and molybdenum iodides, have a strong effect on the activity and the selectivity of the catalysts. As reported previously (ref. 12) the washings with water increase the activity of the catalysts, but to reach high citronellol selectivity, water must be avoided. 

It is well known, even from old literature data (ref. 1) that the presence of metal promotors like molybdenum and chromium in Raney-nickel catalysts increases their activity in hydrogenation reactions. Recently Court et al (ref. 2) reported that Mo, Or and Fe-promoted Raney-nickel catalysts are more active for glucose hydrogenation than unpromoted catalysts. However the effects of metal promotors on the catalytic activity after repeated recycling of the catalyst have not been studied so far. Indeed, catalysts used in industrial operation are recycled many times, stability is then an essential criterion for their selection. From a more fundamental standpoint, the various causes of Raney-nickel deactivation have not been established. This work was intended to address two essential questions pertinent to the stability of Raney-nickel in glucose hydrogenation namely what are the respective activity losses experienced by unpromoted or by molybdenum, chromium and iron-promoted catalysts after recycling and what are the causes for their deactivation ... 

Nickel, either as a Raney catalyst or in the form of nickel boride, is also effective in the reduction of the C=0 bond. An increase in the catalytic activity can be brought about by metal promoters (chromium and molybdenum). Copper chromite may also be used. 

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