Ni-Mo Catalyst

Catalysts in coal liquefaction are used in moving-bed, ebulating-bed, and fixed-bed processes. Disposable iron catalysts must be used in moving beds. More expensive Co-Mo and Ni-Mo catalysts are used in either ebulating or fixed beds, and catalyst deactivation rates and ultimate lifetime are of concern (80, 81). In ebulating beds, a small portion of fresh catalyst is continuously fed to balance the catalyst being purged. 

All the product fractions exhibit lower gravities and higher viscosities and higher heteroatom contents than comparative fractions processed over the more active Shell 324 Ni/Mo catalyst. Particularly outstanding are the higher oxygen levels in the C5-390°F and 390-500°F fractions produced from converted mater-... 

The normalized conversions averaged 12.5 vol.%. Under similar conditions with a more active Shell 324 Ni/Mo catalyst, the 850°F+ conversion would be approximately 40 vol.%. 

Table IV. Supercritical Hydrotreatment of Arabian Topped Crude (ATC) (850F, 11 00 psig, H2 GHSV-300, Nalco Ni-Mo Catalyst)...

Conditions 850F, llOO psig, 300 H2 GHSV, 20 wt lignite extract in toluene, Nalco Ni-Mo catalyst. 

EXAFS studies showed that a nickel atom in a sulfided Ni-Mo catalyst supported on j/-A1203 or on carbon is surrounded by four or five sulfur atoms at a distance of 2.2 A, by one or two molybdenum atoms at a distance of 2.8 A, and by one nickel atom at a distance of 3.2 A (20). These data are consistent with a model in which the nickel atoms are located at the M0S2 edges in the molybdenum plane in a square pyramidal coordination. The nickel atoms are connected to the M0S2 by four sulfur atoms, and depending on the H2S partial pressure a fifth sulfur atom may be present in the apical position in front of the nickel atom (Fig. 4). Recent density functional... 

A third model therefore attributed the promotion effect to cobalt present in the Co-Mo-S phase, with cobalt atoms located at the M0S2 surface a significant contribution of separate Co9S8 was excluded (29). This so-called Co-Mo-S model (or Ni-Mo-S model for Ni-Mo catalysts) is currently the one most widely accepted. 

The ring-number tabulations in Tables II, III, IV, and V are satisfactory for a simplified summary of composition and comparison. The typical Co-Mo or Ni-Mo catalyst commonly used for upgrading will saturate many of the multiple aromatic rings, depending upon severity and activity, but frequently not the last ring of a condensed-ring polyaromatic. Thus, the total number of rings is a measure of the complexity of the hydrocarbon structure. As noted earlier, more detailed data on the distribution of hydrocarbon types in these liquids are available when needed. 

Catalyst Evaluation. Commercial nickel-molybdenum (Ni-Mo) and nickel-tungsten (Ni-W) catalysts were evaluated with this feedstock. The Ni-Mo catalyst was HDS-3A from American Cyanamid and the Ni-W catalyst was Ketjenfine HC-5 from Armak Company. Both were extrudate types supported on alumina and silica-alumina, respectively. The run conditions for the Ni-W evaluation run are shown in Table VII for selected samples. Pressure, liquid feed rate, and hydrogen feed rates were held as nearly constant as possible only the temperature was changed. 

Hydrotreating experiments were conducted on seven naphthas. The range of conditions under which experiments were conducted is as follows 500-2000 psig of pressure an LHSV of 1-4 vol/hr-vol catalyst at 650°-750°F. The catalyst was supported nickel-molybdenum (Ni-Mo), Harshaw HT-100-E, or Cyanamid HDS-9A. Ni-Mo catalysts were used for the presumed nitrogen removal activity. 

Figure 2. Temperature effect upon Ni-Mo catalyst at 2800 psig...

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... 

The results in Table 1 show that for reactions at 425 C significant conversion of the preasphaltenes and the asphaltenes produced at 400 C to other products was possible. In particular for the preasphaltenes >95% interconversion occurred, while for the asphaltene the interconversion was >59%. A complete range of products was formed from high oil yields to repolymerized THF insoluble material. This reactivity underlines the inherent instability of these Intermediate products. The addition of a sulphided Ni/Mo catalyst led to 50% improvement in oil yields. 

The action of sulphided Ni/Mo catalyst was to dramatically increase the yield of oil from the reactions of preasphaltene and asphaltenes. It is believed that the mechanism of the Ni/Mo catalyst involves a more conventional dissociative adsorption of both hydrogen and reactant molecule to the catalyst surface followed by hydrogenolysis and hydrogenation reactions. The mechanistic pathway thus differs from both iron and tin and is shown in Figure 4 by reactions 13 and 14. 

Albenze and Shamsi used DFT to characterize H2S dissociation on Ni(lll) and on two bimetallic surfaces that mimic Ni-Mo solid solutions with <20% Mo. The existence of Mo atoms in the surface layer was found to reduce the energy barriers that exist to H2S dissociation, but this reaction is predicted to be facile on all three surfaces at elevated temperatures. Although some calculations on the effect of surface S coverage were performed, it is not clear how relevant these calculations are to experimental observations with Ni/Mo catalysts, which tend to sulfide rapidly. 

Fig. 6.6. Normalized surface area of MCM-supported catalysts Mo-, Ni-, and Co(Ni)-Mo catalysts in oxide form.

For practical applications, Ni-Mo catalysts generally have higher hydrogenation ability for saturating aromatic ring that is connected to thiophenic sulfur, while... 

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