Nickel-molybdate

Effect of Catalyst The catalysts used in hydrotreating are molybdena on alumina, cobalt molybdate on alumina, nickel molybdate on alumina or nickel tungstate. Which catalyst is used depends on the particular application. Cobalt molybdate catalyst is generally used when sulfur removal is the primary interest. The nickel catalysts find application in the treating of cracked stocks for olefin or aromatic saturation. One preferred application for molybdena catalyst is sweetening, (removal of mercaptans). The molybdena on alumina catalyst is also preferred for reducing the carbon residue of heating oils. 

In treating cracked stocks such as steam cracked naphtha or visbreaker naphtha, which are highly olefinic in nature, nickel molybdate or nickel tungstate catalysts are generally employed. These catalysts have much higher activity for olefin samration reactions than does cobalt molybdate. 

The Exxon Donor Solvent (EDS) Process, developed by the Exxon Research and Engineering Co., differed from the typical process in that, before being recycled, the solvent was hydrogenated in a fixed-bed reactor using a hydrotreating catalyst, such as cobalt or nickel molybdate. Exxon found that use of this hydrogen donor solvent with carefully controlled properties improved process performance. Exxon developed a solvent index, based on solvent properties, which correlated with solvent effectiveness. 

The oxidation of propene to acrolein has been one of the most studied selective oxidation reaction. The catalysts used are usually pure bismuth molybdates owing to the fact that these phases are present in industrial catalysts and that they exhibit rather good catalytic properties (1). However the industrial catalysts also contain bivalent cation molybdates like cobalt, iron and nickel molybdates, the presence of which improves both the activity and the selectivity of the catdysts (2,3). This improvement of performances for a mixture of phases with respect to each phase component, designated synergy effect, has recently been attributed to a support effect of the bivalent cation molybdate on the bismuth molybdate (4) or to a synergy effect due to remote control (5) or to more or less strong interaction between phases (6). However, this was proposed only in view of kinetic data obtained on a prepared supported catalyst. 

Hydrotreating catalysts are composed of cobalt or nickel molybdate or nickel tungstate on an alumina or zeolite support. The materials are sulfided with hydrogen sulfide (H2S) before use, but the final catalysts may retain some oxide and be of complex composition. 

The molybdate surface layer in the molybdenum-alumina samples is characterized by the presence of BrGnsted acid sites ( 1545 cm- ) and one type of strong Lewis acid sites (1622 cm l). Cobalt or nickel ions are brought on this surface on impregnation of the promotor. The absence of BrtSnsted acid sites is observed for both cobalt and nickel impregnated catalysts, calcined at the lower temperatures (400-500°C). Also a second Lewis band is observed at 1612 cnrl.The reflection spectra of these catalysts indicate that no cobalt or nickel aluminate phase has been formed at these temperatures. This indicates that the cobalt and nickel ions are still present on the catalyst surface and neutralize the Brdnsted acid sites of the molybdate layer. These configurations will be called "cobalt molybdate" and "nickel molybdate" and are shown schematically in Figure 11a. 

The catalytic reaction of steam with methane at elevated temperatures (300-400 + C) over various catalysts copper or nickel/molybde-num oxide/alumina—can be made to yield CO and H2 in desired ratios. The generalized reaction for hydrocarbons with steam is ... 

Nickel Molybdate, NiMo04, is prepared by fusing a mixture of sodium molybdate and chloride with nickel chloride. It occurs as green prisms.5 The hydrated ammoniate, NiMo04.NH3.2H20, is obtained as greenish blue prisms by dissolving nickel hydroxide in ammoniacal ammonium molybdate.6... 

Hydrogenation studies were undertaken on the parent iron-tin treated coal (Drum 289) as well as the THF insolubles, preasphaltene, asphaltene and oil derived from a continuous reactor run as previously discussed. Studies with no additional catalyst added (case A) and with the addition of a sulphided nickel molybdate catalyst supported on alumina (case B) were performed. The results are presented in Table 1. The Ni/Mo catalyst in case B did not increase the conversion of the coal or the THF insolubles beyond that for case A because sufficient amounts of iron and tin materials were already... 

On the basis of our present knowledge of the role of iron- and tin-based catalysts and of the role of the sulphided nickel molybdate catalyst the mechanism shown in Figure 4 is proposed to summarize the essential steps in the hydroliquefaction of low rank coals. 

Nickel Molybdates.-—The normal salt, XiMo04, is obtained in the anhydrous condition by fusion of nickel chloride with sodium molybdate and sodium chloride. In the hydrated condition it may be obtained by crystallising from mixed solutions of nickel chloride and sodium molybdate in the cold, a green pentahydrate, NiMo04.5H20,... 

One further difference exists between HDS and HDM. Bridge [37] has shown, very clearly, that HDS is not limited by diffusion while HDM is. Using a nickel-molybdate based catalyst with a unimodal microporous size distribution, the demetalation of Arabian heavy atmospheric residuum was found to be affected by catalyst particle size, while HDS was not. As the diameter of the pore was decreased, the maximum in the metals deposition profile moved closer to the external surface of the pellet, agmn indicating difiusional limitations for FIDM. 

X-ray diffraction was used as a complementary technique and evidenced the formation of a crystallized phase for the regeneration at higher temperatures. The peaks can be attributed to a mixed oxide of molybdenum and nickel with the following formula x (NiO), (M0O3), z (H2O). So the metals partially sinter during regeneration into a bulky phase, which is no longer active. The appearance of this nickel - molybdate type phase, expressed as the area of... 

Keywords nickel molybdate, cobalt molybdate, nickel cobalt molybdate, propane oxidative dehydrogenation, propylene production... 

The most studied systems for oxidative propane upgrading are vanadium [2], vanadium-antimony [3], vanadium-molybdenum [4], and vanadium-phosphorus [5] based catalysts. Another family of light paraffin oxidation catalysts are molybdenum based systems, e.g. nickel-molybdates [6], cobalt-molybdates [7] and various metal-molybdates [8-9]. Recently, we investigated binary molybdates of the formula AM0O4 where A = Ni, Co, Mg, Mn, and/or Zn and some ternary Ni-Co-molybdates promoted with P, Bi, Fe, Cr, V, Ce, K or Cs [10-11]. A good representative of these systems is the composition Nio.5Coo.5Mo04 which was recently selected for an in depth kinetic study [12] and whose mechanistic aspects are now further illuminated here. 

Oxidative Dehydrogenation of Propane by Non-Stoichiometric Nickel Molybdates ... 

Catalysts based on transition metal molybdates, typically bismuth, cobalt and nickel molybdates [2-6], have received recent attention. Of the transition metal molybdates, those based on nickel, and in particular the stoichiometric NiMo04, have attracted the greatest interest. NiMo04 presents two polymorphic phases at atmospheric pressure a low temperature a phase, and a high temperature P phase [2,7]. Both phases are monoclinic with space group dim. These phases differ primarily in the coordination of molybdenum which is distorted octahedral in the a phase and distorted tetrahedral in the P phase. The P phase has been shown to be almost twice more selective in propene formation than the a phase for comparable conversion at the same temp>erature [2]. A similar effect has been noted for oxidative dehydrogenation of butane, with the P phase being approximately three times more selective in butene formation than the a phase [8]. The reason for the difference in selectivities is unknown, but the properties of the phases are known to be dependent on the precursors from which they are derived. Typically, nickel molybdates are prepared by calcination of precipitated precursors. 

The ammonium nickel molybdate precursors were prepared by chemical precipitation [9], Ammonium heptamolybdate ((NH4)jMo70244H20) and nickel nitrate (Ni(N03)2-6H20) were used... 

The catalytic activity of the nickel molybdates [11] was tested in a 1/4 inch quartz flowthrough tubular reactor operated at atmospheric pressure. The reactor was contained within an electrically heated tube furnace. The temperature of the reactor was controlled according to the temperature of the gases at the base of the catalyst bed. The compiosition and flow rate of the gas feed mixture was measured using MKS mass flow controllers calibrated for each specific gas. Certified gas mixtures with Grade 5 helium (99.999%) as the balance gas were used throughout. 

The series of nickel molybdates tested for oxidative dehydrogenation of propane produced a product spectrum limited to propene, carbon dioxide, carbon monoxide, and water. No cracking... 

The series of nickel molybdate catalysts show a decrease in the selectivity towards propene with an increase in conversion. Figure 2 shows the selectivity towards propene at a propane conversion level of 20%. As the Ni/Mo ratio increases above 1, the selectivity towards propene decreases almost linearly as carbon oxides become the dominant products. It is interesting to note, however, that the selectivity towards propene is essentially independent of the Ni/Mo ratio at values less than and equal to 1. This suggests that it is the increase in activity with decreasing Ni/Mo values that accounts for the increase in yield noted above. 

To further improve the yield of propene attainable with the non-stoichiometric nickel molybdates, the oxygenipropane molar ratio was varied from a 1 1 ratio to an oxygen-rich 2.5 1 value. The results of this study are shown in Figure 3. These data were collected at 550 °C with... 

Physical characterization of the phase present under catalytic reaction conditions has shown a single P-phase of Ni,.,.8MO. 8,304 is present at 550 °C following calcination of the (NH4)H2 Ni,. 0(OH)(Mo04)2 precursors [12]. Analysis of the defect chemistry of these non-stoichiometric nickel molybdates identified majority point defects, leading to a correlation between the electrical conductivity and the defect structure [12]. This correlation is summarized below. 

For nickel molybdates having a Ni/Mo ratio greater than one, corresponding to an excess of NiO, the structure is proposed to have interstitial Ni atoms as the major defects that are compensated for by the presence of Mo vacancies. Given this excess of Ni atoms, it was proposed that the majority carrier arises from the oxidation of Ni to Ni", represented by the equation. 

With these two nickel molybdates forming the bounds on the range of Ni/Mo ratios possible, it can therefore be proposed that as the Ni/Mo ratio is varied through this range, the... 

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