Catalyst carriers and a process for their preparation
The present invention relates to new catalyst carriers. It further relates to a process of preparation of these carriers and to their use in the making of catalysts for the conversion of hydrocarbon charges. 
     It is known that the petroleum, petrochemical and chemical industries are increasingly employing processes using catalysts designed to facilitate the desired conversions. These catalysts are combinations of elements such as metals and of carriers well known to the person skilled in the art. In the petroleum industry, for example, alumina, silica and aluminosilicate carriers are widely used. On these have been deposited so-called active phases containing noble metals of group VIII or, generally, the metals of groups III to VIII of the periodic table of the elements, along or in combination with one or more other metals. Active phase means the oxides or sulfides of the metals or, generally, compounds of the metals chosen or the metals themselves (in the metallic state). 
     Among the currently used carriers alumina, particularly, is part of a wide variety of catalysts: 
     As a very common example, the processes for the hydroreforming of hydrocarbons use catalysts generally containing platinum, alone or in combination with one or more other metals, known as promoters, from groups III to VII, such as tin, lead, germanium, rhenium, etc., which are deposited on the alumina by impregnation with solutions of the salts of these metals. The properties of the aluminas here used generally are as follows: A specific surface comprised between 50 and 350 m 2  /g, and a pore volume greater than 0.1 cc/g. 
     Alumina is used also as a carrier for isomerization catalysts which generally contain, in addition to the active phase (comprising a metal such as platinum, possibly in combination with at least one promoter from groups III to VII, for example), a halogen, usually chlorine. 
     Alumina is widely used also as a carrier in hydrocarbon desulfurization catalysts, the active phases deposited on the carrier then comprising metals such as molybdenum, tungsten, cobalt or nickel. These desulfurization processes are coming into even wider use today because of the increasingly more stringent standards imposed on the refiners with a view to lowering the sulfur content of fuels such as gas oil or the fuel oils to a level compatible with reduced pollution. When they contain sulfur compounds, products which are to be burned will, upon combustion, give off sulfur oxides that are harmful to the environment. 
     A special effort has therefore been made to develop advantageous desulfurization techniques of good yield and efficiency whose performance is largely dependent on the use of suitable catalytic formulas. Most often, these are composed of a refractory mineral oxide carrier such as aluminosilicate or an alumina on which active phases such as the aforesaid metals have been deposited. 
     Thus, U.S. Pat. No. 3,509,044 describes a process for the hydrodesulfurization of a petroleum residue in the presence of a catalyst containing a molybdenum salt (the sulfide or the oxide) and a cobalt or nickel salt (the sulfides or the oxides) deposited on a carrier containing silica or alumina. 
     British Pat. No. 1,311,473 describes hydrocarbon desulfurization catalysts containing from 4 to 10% molybdenum, from 1 to 5% nickel or cobalt or a mixture thereof, and from 1 to 5% uranium, deposited on alpha-alumina, these percentages being weight percent. 
     Britich Pat. No. 1,313,005 describes a process for the preparation of a catalyst which consists in impregnating alumina or a silica-alumina mixture with a phosphoric solution of a metal from the molybdenum and tungsten group on the one hand and the nickel and cobalt group on the other hand. 
     Many other publications might be cited that describe desulfurization catalysts which essentially consist of a carrier formed by alumina or a silica-alumina mixture on which at least one active metal from the group consisting of nickel, cobalt, molybdenum, tungsten and uranium has been deposited by impregnation. 
     Other carriers are the subject of many studies. For the isomerization reaction of aromatic hydrocarbons in particular, the behavior of natural zeolites, which are later treated by various cation-exchange processes, is under study. 
     It has been found that the nature of the catalyst carriers has a great influence on the performance of the catalysts prepared with these carriers. 
     The applicant has now developed a new catalyst carrier which may be combined with active phases containing metallic elements from groups III to VIII of the periodic table to make catalysts which are highly effective, particularly in conversion reactions of hydrocarbon fractions, and more particularly the desulfurization of such fractions. 
     A first objective of the present invention thus is to propose new catalyst carriers, particularly for catalysts for the conversion of hydrocarbon fractions. 
     A second objective of the invention is to improve the performance of the processes for conversion of hydrocarbon fractions, and particularly desulfurization, by making use of catalysts comprising carriers perfected in accordance with the invention. 
     The invention has as a first embodiment carriers for catalysts formed of intimate mixtures of aluminum oxide and at least one oxide of a metal selected from groups VIB and VIII of the periodic table of the elements, hereinafter called second metal. 
     The invention has as a second embodiment carriers for catalysts formed of intimate mixtures of aluminum oxide and at least one oxide of a metal selected from the group consisting of nickel, molybdenum, tungsten and cobalt. 
     The invention has a third embodiment a process for the preparation of a catalyst carrier by coprecipitation in the form of a gel from aqueous and/or organic solutions of aluminum and at least one metal from groups VIB and VIII of the periodic table of the elements, said coprecipitation in the form of a gel being followed by drying and possibly calcination of said gel. 
     A fourth embodiment of the invention is a process for preparation of a catalyst carrier by hydrolysis of an aluminum alcoholate with an aqueous solution of at least one water-soluble salt of at least one metal from groups VIB and VIII of the periodic table of the elements, said hydrolysis being followed by drying and possibly by calcination. 
     A fifth embodiment of the invention is a process of preparation of a catalyst carrier by hydrolysis of an aluminum alcoholate with an aqueous solution of at least one water-soluble salt of at least one metal selected from the group consisting of molybdenum, cobalt, nickel and tungsten, said hydrolysis being followed by drying and possibly by calcination. 
     A further embodiment of the invention is the use of the carriers defined above in the making of catalysts, particularly for the conversion of hydrocarbon charges, by combining said carriers with at least one active phase comprising at least one metal from groups III to VIII of the perodic table of the elements. 
     Additionally, still another embodiment of the invention is the use of the carriers defined above in the making of desulfurization catalysts for hydrocarbon charges by combining said carriers with an active phase comprising at least one metal from the group consisting of nickel, cobalt, molybdenum and tungsten. 
     The new carriers prepared by the process developed by the applicant have been found to be formed of an intimate mixture of the various elements entering into their composition. Intimate mixture means that the solids obtained exhibit a very good distribution of the alumina and of the second metal in the mass of the carrier, this distribution being better than that obtained by the usual grinding operations. 
     The proportion of the various constituents of the carrier may vary over a wide range. However, the applicant deems it preferable to limit the weight percent of the oxide of the second metal or of the second metal oxide to 20% and even to about 15% by weight of the alumina, the minimum effective percentage being approximately 0.1 wt. % thus a preferred range is between 0.1 and 20% based on the total mass of the intimate mixture. 
     The process of preparation of these carriers comprises several steps. 
     The first of these is coprecipitation in the form of a gel by hydrolysis, for example, of an aluminum alcoholate -- such as, aluminum isopropylate or an aluminum butylate -- in solution, the concentration thereof varying from 1 to 70% by weight and being preferably about 20% -- for example, in a hydrocarbon such as benzene, toluene or heptane -- with an aqueous solution of a water-soluble salt of at least one metal from groups VIB and VIII, for example, cobalt, molybdenum, tungsten or nickel, of a concentration comprised between 3 × 10 -2  and 1 gram atom per liter of solution. Examples of a water-soluble metal salt are the nitrate or the acetate. However, other salts may also be used. The two solutions -- the organic solution containing the aluminum alcoholate and the aqueous solution containing the metal salt or salts -- are contacted with each other at ordinary temperature or, more generally, at a temperature comprised between 0° and 50° C and then agitated, with a gel then forming. The quantity of water to be used may be from one to three times the stoichiometric quantity for securing precipitation. 
     The gel obtained is subjected to maturing for a period of greater or less duration which may be as long as one or two days but in no case shorter than 10 minutes, the gel being allowed to stand or being agitated. The solvents are then removed by any means known in the art, such as lyophilization, bakeout, filtration, vacuum evaporation, etc. The applicant has successfully used vaporization under subatmospheric pressure. 
     A hydrated gel is thus recovered which has the approximate formula Al 2  O 3  .× MO.3H 2  O, where MO represents the oxide of nickel, molybdenum, cobalt or tungsten. When a plurality of aqueous solutions of salts of different metals have been used, a gel of formula Al 2  O 3 .y MO + z M&#39;O + . . . .3H 2  O is obtained. 
     This gel may be oven-dried at temperatures comprised between 70° and 140° C, or preferably between 80° and 120° C, then possibly calcined at a temperature ranging from 400° to 700° C. 
     After calcination, the textural properties of the solid obtained, which forms the carrier in accordance with the invention, are particularly interesting. The carrier has a specific surface of about 500 to 800 m 2  /g and a pore volume comprised between approximately 1 and 1.5 cc/g. 
     The solid obtained, which is finely divided and is formed of the trihydrated or unhydrated organogel (the water of constitution may have been eliminated during calcination), is steeped in an organic solvent such as toluene or heptane or another liquid hydrocarbon. The amounts of solvent to be added are in the neighborhood of the impregnation volume of the solid. The whole is kneaded for homogenization. 
     The paste obtained is then subjected to peptization with an acid such as nitric acid in solution. Before this operation, the paste may be moistened by the addition of water in amounts which may be as great as 65 or 70 wt. %, based on the weight of the dry gel. The amount of acid necessary for peptization is comprised between 0.5 and 10% and, in general, is less than 5% by weight of the dry gel. The acid, preferably in solution, is added a little at a time, the paste being continuously kneaded. 
     Kneading is continued until separation of the constituents of the mixture sets in, which liberates the organic solvent. The liquid phase is eliminated and the paste is recovered and subjected, under the usual conditions, to an extrusion or any other mode of forming, such as granulation. 
     After this mechanical forming, the solid is dried at a temperature comprised between 70° and 140° C, then calcined at a temperature between 400° and 700° C, and preferably between 500° and 600° C. 
     The solids so obtained are very good catalyst carriers. Their textural properties are about one-half those of the starting solid, their specific surface being comprised between 100 and 500 m 2  /g and their pore volume being greater than 0.1 cc/g. 
     To produce the catalysts, the active phases must then be deposited on these carriers. 
     For example, to produce hydrodesulfurization catalysts, the active phases to be deposited are the metals of groups VIII and VIB of the periodic table of the elements. 
     The technique of deposition used by the applicant is impregnation of the carrier with solutions containing the metals, either in anionic or in cationic form, and in whose composition they enter. After impregnation with these solutions, the solid obtained is dried at between 70° and 140° C, then calcined in air at between 400° and 700° C, and preferably between 400° and 600° C. 
     The percentage of the metals so deposited on the carrier ranges from 1.5 to 20 wt. %, based on the total mass of the catalyst. 
     The catalytic formulas so obtained are particularly effective in processes for the desulfurization of hydrocarbon fractions, particularly the fractions usually called atmospheric gas oil, fuel oils, or vacuum gas oil. 
     Before the hydrocarbon desulfurization operation, it may be advantageous to presulfurize these catalysts by prior-art processes. In general, after they have been placed under hydrogen pressure at between 50° and 200° C, the temperature is raised to about 350° to 400° C while compounds susceptible of liberating sulfur, such as mixtures of hydrogen and hydrogen sulfide, mercaptans or carbon sulfide or even a sulfurous gas oil, are passed over the catalyst. 
     This operation is carried out in the presence of hydrogen. The hydrocarbons to be desulfurized generally are in the liquid phase and the reaction conditions are as follows: The temperature is comprised between 300° and 500° C, the pressure between 30 and 180 bars. The volume ratio between hydrogen and hydrocarbons ranges from 100 to 800 standard liters per liter, and the space velocity (vol./vol./hr.) of the charge, measured in the liquid state, is preferably comprised between 1 and 5. 
     The carriers in accordance with the invention may, of course, be used to make any other type of catalyst for the conversion of hydrocarbon fractions with different active phases comprising, as a rule, at least one metal from groups III to VIII of the periodic table of the elements. 
     The examples which follow are illustrative of the preparation and properties of the carriers in accordance with the invention. They also relate to the making of catalysts for the conversion of hydrocarbon fractions from said carriers and to the uses of said catalysts. These examples are, of course, in no wise limitative. 
    
    
     EXAMPLE 1 
     This example illustrates the preparation of carriers in accordance with the invention. 
     Aluminum isopropylate dissolved in an organic solvent is hydrolyzed, at ambient temperature and with agitation, with an aqueous solution of a water-soluble salt of nickel, tungsten, cobalt or molybdenum. 
     After precipitation of the gel obtained, the solvent is evaporated at a temperature of about 60° C under subatmospheric pressure. 
     This removal of the solvent is followed by a moistening of the gel with water and then by peptization with a 1N solution of nitric acid. 
     After the paste obtained has been kneaded, it is put in the form of extrudates 1.5 mm in diameter, which are then calcined at about 550° C. Table 1 which follows gives the operating parameters of the various steps in the preparation of a dozen carriers, designated A to L. Also presented in that table are, for control purposes, the conditions of preparation of two pure alumina carriers, T1 and T2, prepared under the same conditions, as well as of the two other control carriers, T 1  &#39; and T 2  &#39;, respectively, prepared by hydrolysis of aluminum butylate in place of aluminum isopropylate. 
     
                                           Table 1                                 
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ORGANIC SOLUTION                                                          
                AQUEOUS SOLUTION                                          
                               FORMING                                    
   Weight of    Weight         Volume of                                  
                                     Amount of                            
   aluminum     and            water for                                  
                                     acid for                             
                                           Constitution                   
   isopropyl-   desig-         moistening                                 
                                     peptiza-                             
                                           of solid ob-                   
   ate or       nation    Weight                                          
                               in wt. %,                                  
                                     tion, in                             
                                           tained after                   
   butylate     of        of   based wt. %,                               
                                           calcination                    
Car-                                                                      
   used   Volume of                                                       
                salt      water                                           
                               on    based on                             
                                           (wt.                           
rier                                                                      
   (grams)                                                                
          toluene                                                         
                used      (grams)                                         
                               dry gel                                    
                                     dry gel                              
                                           %)                             
__________________________________________________________________________
   1,386  7.98 1                                                          
                13.6 g    364  63.6  4     99% Al.sub.2 O.sub.3           
A               Ni(NO.sub.3).sub.2 . 6H.sub.2 O                           
                                           1% NiO                         
   792    4.56 1                                                          
                6.64 g    208.8                                           
                               63.5  4     99% Al.sub.2 O.sub.3           
B               Ni(CH.sub.3 COO).sub.2 . 4H.sub.2 O                       
                                           1% NiO                         
   156.8  910 cc                                                          
                3.10 g    40.8 67    1     98% Al.sub.2 O.sub.3           
C               Ni(NO.sub.3).sub.2 . 6H.sub.2 O                           
                                           2% NiO                         
   156.8  910 cc                                                          
                8.05 g    39.8 67    1     95% Al.sub.2 O.sub.3           
D               Ni(NO.sub.3).sub.2 . 6H.sub.2 O                           
                                           5% NiO                         
   156.8  910 cc                                                          
                16.9 g    37   69    1     90% Al.sub.2 O.sub.3           
E               Ni(NO.sub.3).sub.2 . 6H.sub.2 O                           
                                           10% NiO                        
   300    1.72 l                                                          
                0.33 g    79.5 64.5  1     99.6% Al.sub.2 O               
F               ammonium                   0.4% WO.sub.3                  
                para-                                                     
                tungstate                                                 
   300    1.72 l                                                          
                0.83 g    79.5 75.5  1     99% Al.sub.2 O.sub.3           
G               ammonium                   1% WO.sub.3                    
                para-                                                     
                tungstate                                                 
   238    1.37 l                                                          
                2.34 g    62.4 63.5  1     99% Al.sub.2 O.sub.3           
H               hexahydrated               1% CoO                         
                cobalt                                                    
                nitrate                                                   
   235    1.35 l                                                          
                4.8 g     61.2 63.5  1     98% Al.sub.2 O.sub.3           
I               hexahydrated               2% CoO                         
                cobalt                                                    
                nitrate                                                   
   238    1.37 l                                                          
                0.736 g   63.3 65.1  1     99% Al.sub.2 O.sub.3           
J               tetrahydrated              1% MoO.sub.3                   
                ammonium                                                  
                paramolybdate                                             
   235    1.35 l                                                          
                1.476 g   63   63    1     98% Al.sub.2 O.sub.3           
K               tetrahydrated              2% MoO.sub.3                   
                ammonium                                                  
                paramolybdate                                             
   228    1.31 l                                                          
                3.69 g    61.8 63    1     95% Al.sub.2 O.sub.3           
L               tetrahydrated              5% MoO.sub.3                   
                ammonium                                                  
                paramolybdate                                             
T1 156.8  910 cc                                                          
                --        41.6 62    0.5   100% Al.sub.2 O.sub.3          
T2 156.8  910 cc                                                          
                --        41.6 62    1     100% Al.sub.2 O.sub.3          
T.sub.1 &#39;                                                                 
   194.4  400 cc                                                          
                --        65   62    1     100% Al.sub.2 O.sub.3          
T.sub.2 &#39;                                                                 
   194.4  400 cc                                                          
                --        65   62    1     100% Al.sub.2 O.sub.3          
__________________________________________________________________________
 
    
     Table 2 which follows gives the textural properties (specific surface As, pore volume Vp, and average pore radius r) of some of the solids obtained, before being formed (gel) and/or after being formed (extrudates). 
     EXAMPLE 2 
     This example illustrates the preparation of catalysts with the aid of the carriers prepared in Example 1 and the use of said catalysts in desulfurization. 
     (A) PREPARATION OF CATALYSTS 
     The carriers A, B, F, G, H, I, J, L and T 1  &#39;, granulated to 0.5 and 1 mm, are made to undergo an impregnation with a solution of hexahydrated cobalt nitrate and tetrahydrated ammonium paramolybdate in a rotary evaporator in such quantity that the weight percent of oxides of cobalt, CoO, and of molybdenum, MoO 3 , determined after calcination of the solid obtained, are 2.5% and 17%, respectively, based on the total weight of the catalyst. 
     The carriers C, D, E, T1, T2 and T 2  &#39; are granulated to 0.5 to 1 mm, then subjected to impregnation in a rotary evaporator with an aqueous solution of hexahydrated cobalt nitrate and tetrahydrated ammonium paramolybdate in such quantity that the cobalt- and molybdenum-oxides contents of the catalyst finally obtained are 3% and 13.5%, respectively. 
     A portion of the carrier K (herinafter designated K 1 ) is treated in a similar manner as carrier A while another portion of the carrier K (hereinafter designated K 2 ) is treated in the same manner as carrier C. 
     The compositions of the catalysts so obtained are given in Table 3 which follows. 
     
                       Table 2                                                     
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Before Forming    After Forming                                           
      As      Vp      -r    As    Vp    -r                                
Carrier                                                                   
      (m.sup.2 /g                                                         
              (cc/g)  (A)   (m.sup.2 /g)                                  
                                  (cc/g)                                  
                                        (A)                               
______________________________________                                    
A     572     1.07    37    273   0.50  37                                
B     542     1.2     44    280   0.58  42                                
C     573     1.12    39    268   0.46  38                                
D     585     1.12    38    269   0.42  31                                
E     560     0.75    27    253   0.36  28                                
H     --      --      --    284   0.55  39                                
I     --      --      --    278   0.48  35                                
J     --      --      --    290   0.57  39                                
T1    --      --      --    310   0.66  43                                
T2    --      --      --    343   0.64  37                                
T.sub.1 &#39;                                                                 
      --      --      --    277   0.72  52                                
T.sub.2 &#39;                                                                 
      --      --      --    276   0.75  54                                
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                       Table 3                                                     
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                     Active phase (wt. %,                                 
Carrier              based on total weight)                               
                 Second metal                                             
Catalyst                                                                  
       Al.sub.2 O.sub.3  (%)                                              
                 (%)         CoO    MoO.sub.3                             
______________________________________                                    
A      99        1      (NiO)  2.5    17                                  
B      99        1      (NiO)  2.5    17                                  
C      98        2      (NiO)  3      13.5                                
D      95        5      (NiO)  3      13.5                                
E      90        10     (NiO)  3      13.5                                
F      99.6      0.4    (WO.sub.3)                                        
                               2.5    17                                  
G      99        1      (WO.sub.3)                                        
                               2.5    17                                  
H      99        1      (CoO)  2.5    17                                  
I      98        2      (CoO)  2.5    17                                  
J      99        1      (MoO.sub.3)                                       
                               2.5    17                                  
K.sub.1                                                                   
       98        2      (MoO.sub.3)                                       
                               2.5    17                                  
K.sub.2                                                                   
       98        2      (MoO.sub.3)                                       
                               3      13.5                                
L      95        5      (MoO.sub.3)                                       
                               2.5    17                                  
T.sub.1                                                                   
       100              --     3      13.5                                
T.sub.2                                                                   
       100              --     3      13.5                                
T.sub.1 &#39;                                                                 
       100              --     2.5    17                                  
T.sub.2 &#39;                                                                 
       100              --     3      13                                  
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     (B) CATALYTIC HYDRODESULFURIZATION TESTS 
     The catalysts whose modes of preparation have been described above are subjected to hydrodesulfurization tests with two types of hydrocarbon charges, namely, a gas oil (GO) and a vacuum distillate (VGO). 
     The origin of the gas oil is Iraq, its gravity at 15° C is d = 0.8385, its distillation range 219° to 355° C, and its sulfur content, 1%. 
     The vacuum distillate is from a &#34;Safaniya&#34; petroleum. Its characteristics are as follows: 
     Gravity at 15° C: 0.918 
     Viscosity (210° F = 99° C): 6.17 cst 
     Conradson carbon: 0.25 
     Average molecular mass: 380 
     Sulfur content: 2.83% 
     Distillation range: 281° to 510° C (50% distilled point: 444° C) 
     A 10 cc reactor is filled with catalyst, which is presulfurized by means of the gas oil described above at 375° C for 5 hr. The operating conditions of the tests are as follows: 
     
                       Table 4                                                     
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      Hydrogen  H.sub.2 /              Space                              
      pressure  hydrocarbon            velo-                              
Charge                                                                    
      (bars)    ratio        Temp.     city                               
______________________________________                                    
GO    30        180 standard liters                                       
                             375° C                                
                                       5                                  
                per liter of charge                                       
VGO   30        670 standard liters                                       
                             300, 325  3                                  
                per liter of charge                                       
                               350, 375° C                         
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     The results of the tests may be evaluated on the basis of the final sulfur content of the hydrocarbon charge. 
     These results are given in Table 5. 
     
                       Table 5                                                     
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GO charge                                                                 
375° C                                                             
             VGO charge                                                   
Final sulfur Final sulfur, wt. %                                          
Catalyst                                                                  
       %         300° C                                            
                         325° C                                    
                               350° C                              
                                     375° C                        
______________________________________                                    
A      0.05      1.94    1.27  0.76  0.28                                 
B       0.034    1.83    1.26  0.75  0.25                                 
C      0.03      --      --    --    0.30                                 
D      0.05      --      --    --    0.33                                 
E      0.06      --      --    --    0.48                                 
F      0.05      1.82    1.32  0.79  0.35                                 
G      0.05      1.89    1.34  0.81  0.32                                 
H      0.04      1.74    1.26  0.80  0.31                                 
I      0.03      1.80    1.20  0.72  0.28                                 
J      0.04      1.90    1.29  0.79  0.35                                 
K.sub.1                                                                   
       0.04      1.97    1.34  0.71  0.28                                 
K.sub.2                                                                   
       0.05      2.00    1.33  0.79  0.31                                 
L      0.03      1.89    1.31  0.74  0.27                                 
T1     0.09      --      --    --    0.57                                 
T2     0.08      --      --    --    0.50                                 
T.sub.1 &#39;                                                                 
       0.15      2.28    1.56  1.18  0.49                                 
T.sub.2 &#39;                                                                 
       0.09      2.51    1.72  1.26  0.63                                 
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     It is apparent from this table that the catalysts in accordance with the invention are more efficient than catalysts whose carriers contain only pure alumina, the final sulfur content of the hydrocarbon charge being reduced more effectively, under the same test conditions, by catalysts A to L. 
     The applicant has run further identical tests on commercial catalysts prepared by deposition of metals (nickel and/or molybdenum and/or cobalt) on alumina (impregnation with solutions of salts of these metals). Thus it has tested four commercial formulas whose characteristics are as follows: 
     
                       Table 6                                                     
______________________________________                                    
         Co0     MoO.sub.3                                                
                         NiO   As    Vp                                   
Catalyst Wt. %   Wt. %   Wt. % (m.sup.2 /g)                               
                                     (cc/g)                               
______________________________________                                    
T3       4.6     15.2    --    260   0.45                                 
T4       4.2     11.5    &lt;0.01 284   0.55                                 
T5       3.2     13.5    0.07  227   0.50                                 
T6       --      17.5    2.4   142   0.44                                 
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     The tests run on these catalytic formulas produced the following results: 
     
                       Table 7                                                     
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GO charge    VGO charge                                                   
Final sulfur Final sulfur, wt. %                                          
Catalyst                                                                  
       wt. %     300° C                                            
                         325° C                                    
                               350° C                              
                                     375° C                        
______________________________________                                    
T3     0.05      1.91    1.37  0.84  0.36                                 
T4     0.06      2.08    1.54  1.01  0.45                                 
T5     0.06      2.09    1.52  0.98  0.49                                 
T6     0.13      2.26    1.74  1.22  0.63                                 
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     Comprison of the results presented in the above table with those obtained with catalysts A to L in accordance with the invention shows that the latter are more effective, the percent of final sulfur being lower in most cases. 
     EXAMPLE 3 
     This example illustrates the use of catalysts in accordance with the invention in hydrodesulfurization, a test different from that described in Example 2 being performed. 
     The catalytic volume introduced into the reactor here is 160 cc, and the catalyst is in the form of extrudates 1.5 mm in diameter. 
     The operating conditions are as follows: 
     Pressure : 41 bars 
     Hydrogen-to-hydrocarbon ratio: 710 standard liters per liter 
     This test was run on catalyst B described in Example 2, using as charge the vacuum distillate (VGO) with 2.83 wt. % of sulfur as well as three commercial catalysts (catalyst T3, described in the preceding example, and two other catalysts, T7 and T8, whose characteristics are given in Table 8). 
     
                       Table 8                                                     
______________________________________                                    
            CoO      MoO.sub.3                                            
                              As     Vp                                   
Catalyst    Wt. %    Wt. %    (m.sup.2 /g)                                
                                     (cc/g)                               
______________________________________                                    
T7          2.8      14       215    0.40                                 
T8          5.4      11        94    0.33                                 
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     The results obtained (final sulfur, wt. %) under different conditions of temperature and space velocity (vol./vol./hr.) are presented in Table 9. 
     
                       Table 9                                                     
______________________________________                                    
Temperature 350° C                                                 
                    350° C                                         
                            380° C                                 
                                  380° C                           
                                        380° C                     
Space velocity                                                            
            1       3       1     2     3                                 
______________________________________                                    
(Final sulfur,                                                            
            0.19    0.45    0.04  0.09  0.21                              
wt. %)                                                                    
T3 (id.)    0.35    0.76    0.08  0.19  0.29                              
T7 (id.)    0.37    0.79    0.085 0.21  0.32                              
T8 (id.)    0.385   0.81    0.091 0.22  0.33                              
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