CA1139293A - Hydrotreating catalyst preparation and process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Hydrotreating catalysts arc prepared using multiple impregnation and a critical ratio of VIB metal to VIII metal in one or more stages to produce catalysts which have higher than normal activity in contaminant removal from hydrocarbon feed stocks, especially in both sulfur and nitrogen removal. These catalysts also contain relatively low or no acidic residues such as P2O5 and permit the use of lower effective operating temperature for a predetermined percentage of contaminant removal, for example, at 85% removal of sulfur.

Description

~ ~L3r3Z~i This invention relates to an improved VIB metal-VIII metal carrier catalyst suitable for hydrotreating hydrocarbon stocks.
Hydrotreating refers to the processes of hydrodesulfurization, hydrodenitrogenation and demetallization of hydrocarbon feed stocks.
This invention is especially directed toward the preparation of a catalytic composite having superior hydrotreating activity for the removal of sulfur and nitrogen in heavy hydrocarbon s~ocks. Examples of such heavy stocks are total crude oil, crude residua, atmospheric and vacuum gas oils, and cycle oils.
Crude petroleum oil, and heavy hydrocarbon fractions and/or distillates derived from crudes, contain components such as nitrogen, sulfur and metals. These impurities may exist in heteratomic compounds and are often present in relatively large quantities. Such impurities may poison or modify catalysts used in the upgrading of petroleum fractions in reforming or cracking steps. Nitrogen and sulfur are also objectionable because combustion of hydrocarbon fuels containing these impurities releases nitrogen and sulfur oxides. Such by-product gases are noxious, corrosive and present a serious problem in the field of air pollution.
The removal and/or conversion of these impurities is effectively carried out by catalytic hydrotreating, where a feed stock containing sulfur and nitrogen is contacted with a supported catalyst in the presence oE hydrogen. Ilydrotreating conditions may include a wide range of temperatures, pressures and space velocities as determined by the design of commercial refineries.
Supported catalysts can be generally characterized as comprising metallic components, supported on a refractory inorganic ~`~P:~

oxide carrier of synthetic or natural origin, which has a medium to high surface area and a well-developed pore structure. Metallic components having hydrotreating activity often include the metals of Groups VIB and VIII of the Periodic Table.
Numerous disclosures have been made of methods EOI preparing supported catalysts for hydrotreating. Catalytic metals may be applied to a formed or unformed carrier by one of several impregnation methods known to the art. This is usually followed by forming, if necessary, and by calcination to convert the catalytic metal conTpounds to oxides.
Several prior art disclosures have proposed preparing active hydrotreating catalysts by single impregnation techniques using acid stabilized solutions of the catalytically-active metals.
United States, Patent 3,232,887 discloses a method of impreg-nation of catalyst supports, in which the metals impregnating solution is stabilized with an acidic compound. The acidic stabilizer may be organic, e.g., gluconic or citric acid, or inorganic. The preferred acid is phosphoric. The acid stabilized solution contains Group VIB and Group VIII
metals where, in the case of phosphoric acid, the phosphorus to Group VIB
molar ratio, e.g., P/Mo, ranges from .25 to 2.5.
United States Patent 3,287,280 discloses a method of preparing a hydrodesulfurization catalyst by impregnating a formed alurmina suppor-t with a stabilized phosphoric acid solution of molybdenum and nickel salts.
The solut;on contains "at least about 0.2 mole of phosphoric acid per mole of molybdenum metal" and is limlted in some claims to a molar ratio of P/Mo of .2 to .8.

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United States Patents 3,817,873 and 3,755,196 relate to a stable metals solution, a method of preparing the same, a catalyst preparation method using the metals solution, and the resulting catalyst.
The metals solution contains molybdenum, nickel and/or cobaltJ and an acid containing phosphorous, having a P/Mo molar ratio of 0.1 to 0.25.
United States Patent 3,840,~72 discloses preparation of an impregnating solution wherc "the promoter solution of the (disclosed) invention consists essentially of molybdic oxide, at least one of the specified Group VIII metal compounds and phosphoric acid dissolved in water". The solution may contain molar ratios of P/Mo in the range .065 to 2.5.
In addition to the above single impregnation methods with acid stabilized solutions, the prior art discloses methods of preparing hydrotreating catalysts by multiple impregnations and/or stepwise mathods, to incorporate the active metals into the formed or unformed support.
United States Patent 3,11~,701 discloses a catalytic hydrodenitrification process using a catalyst prepared by multiple impregnations of a formed alumina support with aqueous solutions of nickel nitrate and ammonium molybdate, such that the nicke] content of the finished catalyst ;s in the range of ~-10 percent by weight and the molybdenum metal content on the finished catalyst is in the range of 19-30 percent by weight based on the calcined composite.
United States Patent ~,097,~13 claims the preparation of a desulfurization catalyst by first co-mulling boehmite alumina with an aqueous ammonium molybdate solution, drying the resultant mixture, then co-mulling with a soluble cobalt salt. The mixture is then extruded and calcined.

United States Patent 4,048,115 discloses a stepwise method of preparing a desulfurization catalyst. Column 1, line 58, states that "...the present invention relates to a desulfurization catalyst comprising an inorganic oxide carrier material, a Group VIB metal component and a Group VIII metal component wherein said cat~lyst is prepared by (a~ extruding at least 10% of the Group VIII metal component with the inorganic oxide carrier material, and (b) imprcg-nating the resulting extrudate with a sufficient quantity of Group VIB
and Group VIII metal components to yield a finished catalyst containing the requisite metallic component content."
This invention seeks to develop a new hydrotreating catalyst and method for preparing the same. The new catalyst is an improved hydrotreating catalyst having high desulfurization and denitrogenation activity performance. The method of preparation involves a two-stage impregnation using a novel acid stabilized solution in at least one stage.
It is generally known, in the art of hydrotreating catalysis, that cobalt-promoted compositions give better desulfurization selectivity compared to nickel-promoted compositions, while the reverse is true for denitrogenation. This invention seeks to develop a nickel-molybdenum catalyst having unexpectedly-high desulfurization activity compared to its denitrogenation.
It is also generally known in the art bf hydrotreating catalysis that merely increasing the catalytic metals of any composition can eventually top out the activity effect and actually begin to give a ~3~3 decrease in activity at very high metals loadings. This invention also seeks to show that the correct use of a multiple-stage impregnation can allow effective activity use of increased metals loading.
In an alternative aspect, this invention discloses a method of preparing a novel low-level, acid-stabilized impregnating solution.
Ilydrotreating catalysts are prepared using multiple impregnation and a critical ratio of VIB metal to VIII metal in one or more stages to produce catalysts which have higher than normal activity in contaminant removal from hydrocarbon feed stocks, especially in both sulfur and nitrogen removal, which catalysts also contain relatively low or no acidic residues such as P205 and permit use of lower effective operating temperature for a predetermined percentage of contaminant removal, for example, at 85% removal of sulfur.
The general method employed in this invention for the prep-aration of a hydrotreating catalyst includes the following two-step impregnation procedure.

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a. Two impregnating solutions, "A" and "B", are prepared where "A" solution contains Group VIB
and Group VIII metals with a very low level acid stabilization. Solution "B" is a Group VIII
soluble salt solution.
b. A support material is impregnated with the "A"
and "B" metal solutions or the equivalent.
c. The impregnated material, from Steb b, is formed by any method known to the art and calcined.
d. The calcined material, from Step c, is re-impregnated with solution "A" and calcined a second time.
An essential feature of the invention is the preparation of "A" solution. This solution contains about three moles of Group VIB
metal for every one mole of Group VIII metal, with low-level acid stabilization. In general terms, the stabilized "A" solution is prepared by mixing the requisite amounts of Group VIII and Group VIB metals in water with the acid stabilizer. The mixture is then heated and allowed to react sufficiently to give a clear solution. Normally, this takes several hours at 180F. or higher. The volume of the solution may be adjusted with water to the desired concentration.
Some Group VIII metals suitable for use in the in~pregnating solution are the salts of iron, nickel or cobalt. Carbonate salts are preferred. Nickel carbonate is most preferred. Group VIB metals suitable for use in obtaining a stable solution are preferably molyb-denum and tungsten oxides. Molybdenum trioxide is most preferred.

Acid stabilizers that could be used are carboxylic acids such as citric, gluconic, formic and acetic; and certain inorganic oxidic acids. Phosphoric acid is most preferred.
The preferred "A" solution is made with nickel carbonate, molybdenum trioxide and phosphoric acid. Ni-Mo solutions of 120 g/l in MoO3 concentration, or less, were stable for 24 hours without the addition of phosphoric acid. Por concentrations higher than 120 g/l MoO3, it was necessary to add a small amount of phosphoric acid to stabilize the solution for 24 hours. The concentration of the metals in this "A" solution can be varied over a range from 17.5 g/l to 340 g/l MoO3 with a maximum of 20.1 g/l H3P04 required for stabili-zation. That is a maximum molar ratio of P/Mo of 0.087. As previously indicated, solution "B" is the aqueous solution of a soluble salt of a Group VIII metal. The citrate salt is preferred. Nickel citrate is most preferred.
Any support known to the art, as appropriate for hydrotreating, is applicable to this catalyst preparation. Alumina or silica-alumina are preferred.
Several methods of catalyst support impregnation are known to the art, (see, for example, United States 3,232,887). The preferred method for the first impregnation, in this catalyst prepar~tion, is hydrothermal. }lowever, other methods such as pore volume impregnation or co-mulling, are within the scope of this invention. The second-step impregnation may also include several methods known to thc art for dispersing metals in a formed support. The preferred methods for this invention are dipping or pore volumc impregnation. The most preferred method is dipping.

!3Z~3 The catalyst forming may be by any method known to the art. Extrusion and spheridizing are preferred methods.
The following examples are given to illustrate the method of the present invention and the effectiveness of the resulting catalyst for hydrotreat~ng processes. The analytical and activity test results of all example catalyst are given in Table I.

EXAMPLE
This example demonstrates the preparation of the impregna-ting solutions.
, The solution "A" (288 g~l MoO3, 47.5 g/l NiO and 12.4 g/l P2O5) was prepared as follows:
A slurry was made of 9000 ml H2O (70F) with 2880 g MoO3 and 144 ml of 75% H3PO4. The nickel carbonate (820 g) was added ove a period of 15 minutes. The mixture was heated, with agitation, to 200F. and held at that temperature for two hours. A clear green solution was obtained. The solution had a pH of 3.0, with a P/Mo molar ratio of ~087. The volume of the solution was adjusted to 10 liters with water, The solution was indefinitely stable (for at least six months at room temperature).
The solution "B" (106 g/l Nio) was prepared as follows:
Anhydrous citric acid (80 g) was dissolved in 350 ml H2O
t75F). Nickel carbonate (73.3 g) was then added over a period of lS minutes. The slurry was heated s:Lowly t-o 180F. with continual agitation. After one hour of reaction at 180F., a]1 the NiCO3 was in solution and the pH was 3.8. The volume of the solution was adjusted to 400 ml with water.

1~3~3 Three variations of "A" type solutions were prepared to establish the range of phosphoric acid needed to obtain stable Ni-Mo solutions of various metal concentrations.
"A" (variation 1) - A Ni-Mo solution of 120.g/1 MoO3 and 19.8 g/l NiO in metal concentration was prepared by the above "A" method. No phosphoric acid was added. In preparing the solu-tion, 5400 ml H2O (80F), 720 g MoO3 and 203 y NiCO3 were slurried, The mixture was agitated and wa.s heated to 190F. After two hours at 190F., a clear green solution was obtained~ The volume of the solution was adjusted with water to 6000 ml. This solution was stable for about 24 hours after which a green solid precipitated.

"A" (variation 2) - This solution was prepared in the 75%
same manner as in variation 1, except that 36 ml of/H3PO4 was added to the final 6000 ml of solution. This solution ~120 g/l MoO3, 19.8 g/l Nio and 5.15 g/l P2O5) was stable for at least 45 da~s at room temperature. The P/Mo molar ratio of the solution was .087.
"A" (variation 3) - This solution was prepared following the procedure of solution "A", except that the amount of reactants was changed. The amounts were 900 ml H2O, 340 g MoO3, 96 g NiCO3 and 17 ml of 75~ H3PO4. The solution was ad~usted with water to 1000 ml and found to be stable for at least 45 days. The P/Mo molar ratio of the solution was .087. The concentrations of the metal components in the final solution were 340 g/l MoO3, 56 g/l NiO and 14.6 g/l P2Os.
EXAMPLE II
This example demonstrates the preparation of the catalyst of this invention. In this example, solution "A" of Example I is used which contains 288 g/l MoO3 and has a P/Mo molar ratio of .087.

113~3 Thirty-five and three quarter pounds of alumina-silica powder, containing 22% solids, were slurried in 4 liters of water.
The alumina-silica contained 2.8% SiO2 on a dry basis, with the balance essentially A12O3 The slurry was mixed with 2,522 ml of solution "A" of Example I and 844 ml solution "B" of Example I.
The slurry was heated to 200F. and was held at 200F. for one hourO
After the impregnationl the slurry was filtered. The filtrate was saved. The filter cake was dried at 180F. for two hours. The impregnated dried filter cake had a free moisture of 42%, where free moisture was determined on an O-Haus- moisture meter using 10 g of sample which was heated for 20 minutes at a 75 setting.
Eighteen pounds of the dried filter cake were charged to a Simpson muller. The filtrate (3800 ml) was added to the muller. The material was mulled for 20 minutes and then was extruded at 55~
free moisture through a 0.073 inch die. The extrudates were pre-dried at 300F. for 3 hours and then calcined at 1100F. for 2 hours The calcined, impregnated extrudates, after the first impregnation, contained 17% MoO3, 3~73~oNiO and 0.78% P2O5 by weight. Five pounds of the above extrudate were dipped into 9080 ml solution "A" for 16 hours. After the impregnation, the solution was drained off and the impregnated catalyst was predried at 300F. and then calcined at 1100F. for two hours.
The finished catalyst contained 28% MoO3, 6.4% NiO and 3.1% P2Os by weight. Chemical analyses are given in Table I.

EXAMPLE III
This example serves as a comparison for Example II where the dipping time was reduced from 16 hours to 1 hour. All other catalyst preparation steps are the same as Example II. Analysis results are shown in Table I.

EXAMPLE IV
This example shows the effect of lower metals levels afte the first impregnation. The catalyst was prepared in the same manner as the catalysts in Examples II and III, with the exception that the metals in the calcined extrudate after the first impregna-tion were 11.8~ MoO3, 3.51% NiO and 0.50% P2O5 by weight. After a one-hour dip, second impregnation, the finished catalyst contained 26.2~ MoO3, 5.59% NiO and 1.6% P2O5by weight. The analytical results are given in Table I.

EXAMPLE V
This example further reduces the metals after the first impregnation such that extrudate, after the first impregnation, contained 5.9% MoO3, 3.08% Nio and .05% P2O5 by weight. In addition the first stage metals impregnation was done by adding the metals as MoO3, NiC03and citric acid, in their solid form, rather than as solutions "A" and "s". In all other ways, the preparation of the finished catalyst followed the procedure described in Examples III
and IV. The final catalyst contained 23.6% MoO3, 5.76% NiO and 1.3 P2O5 by weight. The analytical results are tabulated in Table I.

EXA~IPLE VI
This example shows the effect of eliminating the Group ¦VIB metal entirely from the first irnpregnation step~ The procedure of Example V was followed, except that only nickel carbonate and citric acid were used in the impregnation of the alumina-silica support. The first-stage impregnated extrudates contained 2.85% NiO, and the second-stage impregnated catalyst contained 22.8% Mo~3, 5.85% NiO and 1.4% P2Os by weight. Analytical results are shown in Table I.

~ 1 1139Z~3 EXAMPLE VII
This example shows the effect o~ the solution concentra-tion, in the final impregnation, on catalyst activity.
The calcined extrudates through the first-stage impregna-tion were prepared according to the procedure described in Example IV~ In the second-stage impreynation, 454 g of the calcined extxu-date were dipped into 1816 ml of impregnation solution "A" having a concentration of 200 g/l MoO3 concentration (instead of 288 g/l in MoO3 concentration as in Example IV). Analytical xesults are shown in Table I.
EXAMPLE VIII
, This catalyst was prepared by the same method as Examples IV and VII, except that the concentration of solution "A" was 120 g/l MoO3 in the final impregnation step. Analytical results are shown in Table I.

EXAMPLE IX
This example shows the use of pore volume irnpregnation in the second-stage of impregnation. The calcined extrudates obtained after the first-stage impregnation were prepared in a method similar to Example II to give a material containing 14.6% MoO3, 4.55% Nio and 0.93% P2O5 by weight. This support (7302 g) was impregnated with 4,554 ml of solution "A" (288 g/l MoO3) by introducing the liquid to a tumbling, evacuated bed of the extrudate. The impregna-ted extrudates were dried and calcined at llOO"F. for 2 hours.
Analytical results are tabulated in Table I.

~13'~ 3 EXAMPLE X
This example demonstrates the use of the invention catalysts for hydrotreating. Eaeh of the eatalysts of Examples II
to IX were tested for hydrotreating aetivity. The activities were ~etermined in comparison to a commercial Ni-Mo hydrotreating eatalys :.
The analysis of the referenee eatalyst is given in Table I, Example X. Sixty milliliters eaeh of the experimental catalyst to be evaluated and the reference catalyst were tested for desulfurization and denitrogenation aetivity on a heavy vaeuum gas oil (gravity API 20.0, boi7ing range 742-1065F) containing 2.8~ sulfur by weight and 1560 ppm nitrogen. The run conditions were 675F., 1000 psig, 1.5 LHSV (vol oil/hr/vol catalyst) and 4100 scf/bbl hydrogen. The catalysts were charged to adjacent tube reactoxs in an isothermal sandbath.
The referenee catalyst was assigned a standard activity value of 1.00 on a volume basis. The activities of the experimental catalysts are reported relative to this standard on a volume basis.
The activity results are yiven in Table I.

EXAMPLE XI
The following example illustrates the superior activity maintenance of the invention catalyst when compared with a commer-cial Co-Mo eatalyst when desulfurizing a blend of vacuum gas oil and vacuum residuum. This feed is more difficult to treat than vacuum gas oil or lighter distillates alone. The invention catalyst tested in this example was prepared by a procedure similar to that of Example II. The above catalysts ~1/16" extrudate) were charged in 1139~3 qual volumes to identical electrically-heated pilot plant tubular ~ ¦
reactors, given a standard presulfiding activation treatment and placed on stream, desulfurizing a feed blend as described below.
Reactor temperatures were increased as required to maintain 85%
desulfurization and the experiment continued at the conditions shown below for 24 days. The superior activity maintenance of the inventi n catalyst is shown by both a lower operating temperature and a smalle rate of temperature increase over the extended operating period.
Feed Properties (Blend) Gravity, API 25.;7 , Flash point, F (COC) 305 Ramsbottom Carbon, Wt.% 1.91 Sulfur, Wt.% 0.62 Nitrogen, Wt.% 0.114 Distillation, ASTM D-1160 IBP, F 418 10% 572 50% 751 90% 1055 Run Conditions Start-of-run temperature, F 690 Reactor pressure, psig 1225 Oil liquid hourly space velocity/hr 1~7 Hydrogen/oil ratio, scf/hbl 2000 1139Z~3 Invention Catalyst Properties MoO3 27%
NiO 6.7%
P2O5 2.25~
ABD .92 gm/ml Activity Results Days on Stream Temperature Required for 85% Desulfurization, F.
Invention Catalyst Reference Catalyst 698 . 702 , 15 710 721 113~Z~3 Il- xl II~ C~

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Evaluation of Results The examples illustrate several properties of the invention catalyst which are unique and support the objectives of this invention.
The data in Table I show that over a wide range of preparative conditions the invention catalyst gave activity superior to the commercial nickel-molybdenum catalyst in both denitrogenation and desulfurization. Further, in every case, the desulfurization activity was improved an additional four to twenty-six percent over the denitrogenation improvement.
Example XI illustrates superior desulfurization activity, even to a commercial cobalt-molybdenum catalyst.
The Group V B metal, added to the catalyst in the first step, varies from zero to 17%, with the best activity improvement occurring at the higher levels, (Examples II, III, IV, V, VI). The second-stage impregnation is illustrated either by dipping or by pore volume impregnation. In the dipping examples, the time varied from one to sixteen hours, (Examples II and III) and the dipping solutions varied from 120 g/ml MoO3 to 288 g/l MoO3 in concentration (Examples IV, VII and VIII).
In general, as shown by the examples, these catalysts should preferably contain 21-30% MoO3, 5-7% NiO and 1,0-3.5%
P2O5. The molar ratio of Group VIB metal to Group VIII metal in the "A" solution of approximately 3:1 appears to be critical.
The multiple stage impregnation of the catalyst carrier is also an important feature of the invention using impregnating solutions of the type herein described.

. ~ ~ ~3~3 . l In addition, significant improvement has been obtained by using the dippins method of impregnation as distinguished from other methods such as pore volume impregnation.
The ability of a catalyst to desulfuri.~e a hydrocarbon feedst~ck at a predetermined high rate of desulfurization with lower temperatures as demonstrated by Example YI is a very impor-tant factor in processes of this type because the use of lower temperatures results in lower costs~.

Claims (27)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of a hydrotreating catalyst containing at least one Group VIII metal and at least one Group VIB metal which comprises:
(a) preparing a stable, clear aqueous solution of a compound of at least one Group VIB metal and of at least one Group VIII metal, wherein the molar ratio of Group VIB metal to Group VIII metal is approximately 3:1, to provide a solution "A";

(b) preparing separately an aqueous solution of a compound of at least one Group VIII metal, to provide a solution "B";
(c) impregnating a hydrotreating catalyst carrier with both solutions "A" and "B" until a desired metals level is obtained;
(d) filtering, semi-drying, forming and calcining the product from step (c);
(e) impregnating the calcine from step (d) with only solution "A" until a desired metals level is reached;
(f) drying and calcining the product from step (e) to provide the desired catalyst.

2. A process according to claim 1, wherein the Group VIB
metal is chosen from molybdenum and tungsten.

3. A process according to claim 1, wherein the Group VIB
metal is molybdenum.

4. A process according to claim 1, wherein the Group VIII
metal is iron, nickel or cobalt.

5. A process according to claim 1 or 3, wherein the group VIII metal is nickel.

6. A process according to claim 1 or 3, wherein the group VIII metal is cobalt.

7. A process as claimed in claim 1, wherein solution "A"
is stabilized by addition thereto of a minor amount of phosphor-ic acid not exceeding that corresponding to a molar ratio of phosphorus to Group VIS metal of 0.087:1.

8. A process according to claim 7, wherein the Group VIB
metal is molybdenum.

9. A process according to claim 8 wherein solution "A"
contains from 120 g/l to 340 g/l molybdenum expressed as MoO3 and phosphonic acid sufficient to provide a molar ratio of phosphorus to molybdenum of approximately 0.087:1.

10. A process according to claim 1 wherein the impregnat-ion, in step (c), is hydrothermal.

11. A process according to claim 1, wherein the impregnat-ion, in step (c), is dry dipping.

12. A process according to claim 1, wherein solution "B"
additionally contains an effective amount of an organic solu-bilizing acid.

13. A process according to claim 12, wherein the solubil-izing acid is citric acid.

14. A process according to claim 1, wherein the Group VIB
metal is molybdenum, and the Group VIII metal is nickel.

15. A hydrotreating catalyst comprising a hydrotreating catalyst carrier together with an effective amount of both a Group VIB metal compound and a group VIII metal compound obtained by:
(a) preparing a stable, clear aqueous solution of a compound of at least one Group VIB metal and of at least one Group VIII metal, wherein the molar ratio of Group VIB metal to Group VIII metal is approximately 3:1, to provide a solution "A", (b) preparing separately an aqueous solution of a com-pound of at least one Group VIII metal, to provide a solution "B";
(c) impregnating a hydrotreating catalyst carrier with both solutions "A" and "B" until a desired metals level is obtained;
(d) filtering, semi-drying, forming and calcining the product from step (c);
(e) impregnating the calcine from step (d) with only solution "A" until a desired metals level is reached;
(f) drying and calcining the product from step (e) to provide the desired catalyst.

16. A catalyst according to claim 15 wherein the Group VIB metal is molybdenum or tungsten.

17. A catalyst according to Claim 15, wherein the Group VIII metal is molybdenum.

18. A catalyst according to claim 15, wherein the Group VIII metal is iron, cobalt or nickel.

19. A catalyst according to claim 15, wherein the Group VIII metal is cobalt.

20. A catalyst according to claim 15, wherein the Group VIII metal is nickel.

21. A catalyst according to claim 15, containing phosphonic acid residues deriving from a stabilizing amount of phosphonic acid used in solution "A".

22. A catalyst according to claim 21, containing from about 21%-30%
molybdenum expressed as MoO3, from about 5% to about 7% nickel expressed as NiO, and from about 1% to about 3.5% phosphorus expressed as P2O5.

23. A process of hydrotreating hydrocarbon feed stocks to remove one or more of the elements sulfur, nitrogen and metals which comprises subjecting such feed stocks to catalytic conversion in the presence of a catalyst as claimed in claim 15, 16 or 17.

24. A process of hydrotreating hydrocarbon feed stocks to remove one or more of the elements sulfur, nitrogen and metals which comprises subjecting such feed stocks to catalytic conversion in the presence of a catalyst as claimed in claim 18, 19 or 20.

25. A process according to claim 3 wherein the molar ratio of molybdenum to Group VIII metal is from 3.14:1 to 3.26:1.

26. A catalyst according to claim 17 wherein the molar ratio of molybdenum to Group VIII metal is from 3.14:1 to 3.26:1.

27, A process of hydrotreating hydrocarbon feed stocks to remove one or more of the elements sulfur, nitrogen and metals which comprises subjecting such feed stocks to catalytic conversion in the presence of a catalyst as claimed in claim 21, 22 or 26.