Sulfided 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... 

The use of axidie or sulfided Ni/Mo catalyst or of an unimpregnated catalyst carrier made no difference as concerns the amount ox coke formed or PNAs removed from the feed. Experiments at 375°C and 200°C gave the same amounts of coke both on the carrier and on the catalyst... 

Hillerova et al. [71] compared the performance, in parallel HDN of pyridine and HDS of thiophene, of sulfided Ni-Mo catalysts supported on alumina and on a special carbon named Sibunit, which is based on graphitized carbon black and is mainly mesoporous [79]. The carbon-supported catalysts showed a higher resistance to inhibition by pyridine, higher HDN activity, and a higher HDS/HDN activity ratio than that of the commercial alumina-supported catalyst. 

Figure 12 shows the S mSat process based on published information. 120,179,180 SynSat process is considered to be an iimovation across the boundary between catalysis and reactor engineering . SynSat employs several different catalyst beds within a single reactor shell with intermediate by-product gas (H2S etc.) removal, and optional counter-current gas-flow. Catalysts A and B in Figure 9 are metal sulfide catalysts such as sulfided Ni-Mo. Catalyst C is a noble metal loaded on an acidic support such as zeolite. There is an intermediate gas removal between the beds of Catalysts B and C. Nearly all the sulfur compounds must be converted and removed as H2S on beds A and B before the fuel feed reaches the noble metal catalyst bed C. 

Calcined and sulfided Ni-Mo catalysts supported on ultrastable Y zeolite, NaY, mordenite and ZSM-5 were studied by high-resolution TEM [271]. In USY zeolite, Ni-Mo-S clusters were found in the supercages of the zeolite, whereas, on other zeolites, the sulfide phase was predominantly on the external surface. Bendezu et al. [272] also studied the dispersion and location of Ni-S, W-S and a Ni-W-S phase in US zeolite. 

A total operating pressure of 1400 psig and sulfided Ni-Mo AI2O3 catalyst were used in these experiments. The shale oil had the following elemental analyses C, 81.5 H, 10.1 N, 2.3 S, 1.0. 

The chemical properties of tungsten are similar to those of molybdenum tungsten is more expensive, however, and its industrial use is therefore limited. Especially when hydrogenation is carried out under severe conditions, such as in hydrocracking, sulfided Ni-W/A Os catalysts have advantages over sulfided Ni-Mo/Al203. 

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. 

Figure 3 Effect of temperature on saturation of total polyaromatics in a gas oil over sulfided Ni/ Mo/Alumina catalysts. LHSV = 2 L7(L h) P = 750 psig hydrogen/oil = 2(XX) scf/bbl. (From Ref. 4.)...

An alternative way for thiophene synthesis is the dehydrogenation of tetrahydrothiophene (THT). This molecule is easily produced, with an excellent yield, by oxygen/sulfor substitution in tetrahydrofuran. THT dehydrogenation was studied by different authors on sulfided Ni, Mo or Co-Mo catalysts. Recently Lacroix et al [5] performed an extensive study of the reaction on unsupported sulfides. 

E23.3 Anisole is an oxygenated compound contained in the bio-oil, may be used with the process of HDO with Co/Mo or Ni/Mo catalyst supported on alumina. The anisole can be transformed to phenol and then can be hydrodeoxygenated, as suggested by Viljava et al. (2000). These authors used C0M0/AI2O3 sulfide catalyst. 

Mixed-Metal Sulfides. Mixed-metal sulfides are generally prepared by one of the four following methods 1) comaceration, (2) homogeneous sulfide precipitation, (3) mixed-metal salts or organometallic clusters decomposition, and 4) impregnation of a binary sulfide. Most of these techniques were developed for the synthesis of Co/Mo or Ni/Mo catalysts but are applicable to other systems. 

The acid component of a hydrocracking catalyst can be an amorphous oxide, e.g., a silica-alumina ora zeolite, eg., USY. This component usually serves as a support for the metal compound responsible for the hydrogenation function. The metal compound can be a noble metal, e.g., Pt or Pd, or a mixture of sulfides, e.g., of Ni/Mo, NiAV, or Co/Mo. The relative amounts of the respective compounds have to be thoroughly balanced to achieve an optimum performance. 

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