HYDROTREATING CATALYST AND PROCESS OF MANUFACTURE

Abstract: Hydrotreating catalyst comprising alumina or alumina-­ containing carrier containing 2 to 35 weight % silica and Group VIII and/or Group VIB metals as hydrogenation active components. The carrier is characterized by a maximum of pores in the range of from 30 to 100 Å (30 × 10¹⁰ to 100 × 10 ¹⁰m) and a minimum of pores in the respective ranges of from 0 to 30 Å (0 to 30 × 10 ¹⁰m) and 300 Å+ (300 × 10 ¹⁰m and greater). Preparation includes a first step impregnation with at least one Group VIII metal and a second step impregnation with at least one Group VIB metal. Preferably the impregnation is via ion exchange using a complex salt, preferably an ammine or amine salt, of the metal.

Description: This invention relates to a catalyst useful in the hydrotreatment of hydrocarbon oils and to a process for producing such a hydrotreating catalyst as well as to the use of such a catalyst in the hydrotreatment of hydrocarbon oils. More particularly, this invention relates to a hydrotreating catalyst comprising an alumina or an alumina-containing carrier which also contains a specified silica content and preferably by a specified pore size distribution, this carrier supporting hydrogenation-active components in a well-dispersed state. In the description of this invention, the terms "hydrotreating" or "hydrotreatment" refer to various processes for treating a hydrocarbon oil by contact with hydrogen, which include hydrofining under reaction conditions of relatively low severity, hydrofining under reaction conditions of relatively high severity accompanied with an appreciable cracking reaction, hydroisomerization, hydrodealkylation, and other reactions of hydrocarbon oils in the presence of hydrogen. Hydrodesulfurization, hydrodenitrogenation, and hydrocracking of distillates and residual oils from atmospheric and vacuum distillation processes are examples of such processes as are the hydrofining of a kerosene fraction, a gas oil fraction, wax, or lubricating oil fractions. Since the catalyst of this invention is suitably used in performing hydrodesulfurization of atmospheric middle distillates such as kerosene fraction and gas oil fraction, vacuum heavy distillates, residual oils containing asphalt, or mixtures thereof, the explicit description in this specification of the use of the catalyst will be made chiefly in connection to hydrodesulfurization. Desulfurization processes comprising hydrofining a sulfur-containing hydrocarbon oil in the presence of a catalyst containing hydrogenation-active components have long been known, and nowadays the establishment and improvement of a hydrodesulfurization process whereby heavy hydrocarbon oils containing asphalt and metal-containing compounds can be desulfurized industrially is eagerly desired as a nonpolluting process. Moreover, the residual oils contain nitrogen compounds in addition to the sulfur compounds and as a result nitrogen oxides are formed upon combustion of such oils. The oxides of both sulfur and nitrogen are undesirable atmospheric pollutants. The sulfur and nitrogen compounds contained in hydrocarbon oils can be removed in the forms of hydrogen sulfide and ammonia, respectively, by a hydrogenation reaction in the presence of a catalyst. However, heavy hydrocarbon oils, especially residual oils, contain catalyst poisoning substances, for example, organic compounds of metals such as vanadium or iron, which remarkably lower the activity of a catalyst and further prevent its regeneration. Further, residual oils contain high-molecular compounds of polynuclear aromatics such as asphaltene and asphalt, and these compounds cover the active sites of the catalyst, and cause the formation of carbonaceous deposits which block the pores of the catalyst so as to lower its activity. Thus, the hydrofining of a heavy hydrocarbon oil must cope with extremely difficult technical problems. Heretofore, a variety of investigations have been made about catalysts for use in the hydrodesulfurization of residual oils. For example, a process is known from Japanese patent publication No. 38142/1970 in which a catalyst having a pore size distribution in which the volume of pores having a diameter of at least 80 Angstroms (8 nm) is limited to below 10 percent of the total pore volume is used to prevent intrusion of the asphalt and metal-containing compounds contained in the feed oil into the pores. Similarly, a process is known from Japanese patent publication No. 38143/1970 in which a catalyst in which pores having a diameter of below 120 Angstroms (12 nm) are distributed relatively uniformly at intervals of 10 Angstroms (1 nm). Further, there is also in disclosed in Japanese patent laid open 10356/1972 a catalyst for hydrodesulfurizing crude petroleum or topped crude petroleum in which the volume of pores having a diameter in the range of about 50 to 100 Angstroms (5 to 10 nm)accounts for at least 50 percent of the total pore volume and the volume of pores having a diameter in the range of 0 to 50 Angstroms (0 to 5 nm)accounts for at most 25 percent of the total pore volume. Additionally, in the hydrodesulfurization in the petroleum refining, there has heretofore been widely used [see Muralidhar G., J. Cat., 85 , 44-52 (1984) and Oil & Gas J., p73, 14 Oct 1985] a hydrotreating catalyst produced by allowing an alumina carrier to support at least one metal selected from the group consisting of Group VIII metals of the Periodic Table of Elements and/or Group VIB metals of the Periodic Table of Elements, for example, a cobalt/molybdenum catalyst or a nickel/molybdenum catalyst. It is the most important factor in the production of such a hydrotreating catalyst to allow a carrier to support a large amount (about 20 percent or more by weight in terms of an oxide) of molybdenum/cobalt or molybdenum/nickel particles of a uniform composition in a highly dispersed state. Moreover, the inventors have discovered that the pore size distribution of a catalyst comprising hydrogenation-active metals is important for obtaining excellent catalytic properties, activity and activity maintenance as hydrotreating catalysts and that this pore size distribution should be limited to a specified range. Proposed processes for producing a hydrotreating catalyst include (1) a coprecipitation process (Shokubai Chousei, pages 20-21 (Koudansya)), (2) a kneading process (Shekubai, 20 , 107(1978), Catalysis Society of Japan and Ind. Eng. Chem. 35 , 1160(1943) and (3) an impregnation process (Japanese Patent Laid-Open No. 24047/1981 and A.C.S preprint, March 23-28(1980)p255), all of which have been generally put into practice. The coprecipitation process, however, has a drawback that when a plurality of active metal components are used as in the case of the above-mentioned hydrotreating catalyst, it is difficult to disperse these active metal components uniformly and to produce a catalyst with good reproducibility. The kneading process also has a drawback that although it is necessary to ensure sufficient access of a plurality of active metal components to a carrier as well as their uniform and perfect mixing in producing a hydrotreating catalyst having a plurality of active metal components as above, attainment of such a state is extremely difficult in this process. As compared with the above two processes, the impregnation process may be thought suitable for the production of a hydrotreating catalyst having a plurality of active metal components as described above, for example, an alumina-supported cobalt/molybdenum or nickel/molybdenum catalyst. In the production of a hydrotreating catalyst by the impregnation process (see: A.C.S. preprint, 23-28 March 1980, p255; J. Phys. Chem., 82 , p889(1978) and 3rd International Conference on the Chemistry and Uses of Molybdenum, p73(1979)), a process (two-step impregnation process) has been proposed which comprises using alumina generally as a carrier, allowing the carrier to support first molybdenum (first step), and then allowing the carrier to support cobalt or nickel in the form of fine particles of molybdenum/cobalt or molybdenum/nickel which are formed by the interaction between said active metal and molybdenum (second step). However, it is difficult to allow the carrier to support molybdenum in an amount of as large as about 15 percent by weight in a highly dispersed state in the first step, and the dispersibility in the catalyst obtained finally is virtually determined by the state of dispersion of molybdenum in said first step, which inevitably leads to decrease in activity. The above-mentioned problem of the impregnation process may be solved by using a process which comprises allowing an alumina carrier to support cobalt or nickel in the first step, and then allowing the carrier to support molybdenum, but no desired performances can be obtained in this case because when active metal components such as cobalt or nickel are supported on the alumina carrier, they do not show sufficient interaction with the alumina carrier and lose their activity by forming agglomerates of inactive Co₃O₄ or cobalt aluminate. Further, a process comprising allowing an alumina carrier to support a plurality of active metals simultaneously by impregnation is not preferred because it is difficult to distribute all the components uniformly throughout the carrier. As described above, it is extremely difficult in producing a catalyst containing large amounts of supported active metal components and carrying a plurality of active metal components, such as a hydrotreating catalyst, to allow the carrier to support all the components in a uniform and highly dispersed state by the conventional methods. US-A-4134856 describes and claims a hydrorefining catalyst comprising at least one hydrogenation metal or an oxide or a sulfide of a metal selected from the group consisting of Group VIB metals and Group VIII metals and mixtures thereof supported on an alumina carrier containing from about 5 to about 25 weight % silica, said catalyst having a specific surface area in the range of from about 250 to about 300 m²/g and a pore volume distribution characterized in that (1) the volume of pores having a diameter of 60-150Å (6-15 nm) is at least about 80% of the volume of pores having a diameter of 0-150Å (0-15 nm), (2) the volume of pores having a diameter of 150-300Å (15-30 nm) is less than about 20% of the volume of pores of 0-300Å (0-30 nm), (3) the volume of pores having a diameter of 0-600Å (0-60 nm) is in the range of from about 0.45 to about 0.60 ml/g, and (4) the volume of pores having a diameter of 150-2000Å (15-200 nm) is less than about 0.01 ml/g. EP-A-16599 describes and claims a process for hydrotreating a hydrocarbon stream to remove nitrogen and sulfur which process comprises contacting a hydrocarbon stream comprising a stream selected from petroleum distillate, tar sands distillate, and shale oil, with hydrogen and a catalyst comprising a porous refractory inorganic oxide and deposited thereon hydrogenation components comprising chromium, molybdenum and at least one Group VIII metal, said catalyst having a pore volume distribution comprising 20-50% of pore volume in pores with diameters of 0.50 Angstrom units (0-5 nm), 30-70% of pore volume in pores with diameters of 50-100 Angstrom units (5-10 nm), 0-20% of pore volume in pores with diameters of 100-150 Angstrom units (10-15 nm), and 0-10% of pore volume in pores with diameters greater than 150 Angstrom units (15 nm). SUMMARY OF THE INVENTION The present invention provides a method of preparing a hydrotreating catalyst, said method comprising the following steps in the stated sequence: (a) providing a carrier formed of silica/alumina or a silica/alumina-containing substance, said carrier containing silica in an amount of from 2 to 35% by weight (e.g. from 7 to 12% by weight); (b) thereafter causing said carrier to initially support first at least one metal selected from the group consisting of Group VIII metals of the Periodic Table of the Elements, said selected Group VIII metal being contained in an amount of from 0.5 to 20% (e.g. from 2 to 5%) by weight in terms of an oxide; (c) thereafter causing said carrier containing said Group VIII metal to support at least one metal selected from the group consisting of Group VIB metals of the Periodic Table of the Elements, said selected Group VIB metal being contained in an amount of from 5 to 30% (e.g. from 12 to 20%) by weight in terms of an oxide; and (d) thereafter recovering said hydrotreating catalyst. The inventors of this invention have discovered that cobalt and/or nickel as well as other Group VIII metals which are active metal components of a hydrotreating catalyst can be supported on the particular active points of a silica/alumina carrier or a silica/alumina-containing carrier, and that cobalt and/or nickel and/or other Group VIII metals may be supported stably in good dispersibility in a first step by replacing a conventional alumina carrier with a silica/alumina carrier or a silica/alumina-containing carrier. This is probably because cobalt and/or nickel and/or other Group VIII metals are supported on the acid sites of silica/alumina by a chemical interaction, and we have found that when a silica/alumina carrier or a silica/alumina-containing carrier is allowed to support cobalt and/or nickel and/or other Group VIII metals by ion exchange, the dispersibility of the metal can be markedly improved. Furthermore, it has been found that the silica/alumina carrier which is allowed to support cobalt and/or nickel and/or other Group VIII metals in the first step as above may further be allowed to support molybdenum and/or other Group VIB metals in the second step, and that at this time molybdenum, as an example, is supported around cobalt and/or nickel, for example, by an interaction between molybdenum and cobalt and/or nickel, so that fine particles of molybdenum/cobalt or molybdenum/nickel may be supported in a uniform and highly dispersed state. As described above, the inventors of this invention have found that, when silica/alumina or a silica/alumina-containing substance is used as a carrier, cobalt and/or nickel and/or other Group VIII metals act as a promoter and, at the same time, function as an anchor for molybdenum, and/or other Group VIB metals, so that it is effective in improving the dispersibility and stability of molybdenum and/or other Group VIB metals as active metal components. Accordingly, one embodiment of this invention resides in a process for producing a hydrotreating catalyst characterized by using silica/alumina or a silica/alumina-containing substance as a carrier, allowing the carrier to support first at least one metal selected from the group consisting of Group VIII metals of the Periodic Table of Elements, and then allowing the carrier to support at least one metal selected from the group consisting of Group VIB metals of the Periodic Table of Elements. Particularly, this invention demonstrates that good catalytic activity can be obtained even by the use of lesser amounts of a Group VIII metal on a support. In the process for producing a hydrotreating catalyst according to this invention, a silica/alumina or silica/alumina-containing carrier having acid sites is used instead of an alumina carrier. When silica/alumina or a silica/alumina-containing substance is used as a carrier and is allowed to support at least one Group VIII metal of the Periodic Table of Elements in the first step, the metal may be supported in a stable, well-dispersed state because said active metal component is bound to the acid sites of the silica/alumina. It is thus possible to allow the carrier to support at least one Group VIB metal of the Periodic Table of Elements, which is the principal active metal, outside a Group VIII metal, that is, on the layer of the Group VIII metal, by supporting the Group VIII metal in a well-dispersed stage on the acid sites of a carrier in the first step, and therefore the catalyst of this invention is extremely suitable as a hydrotreating catalyst. On the other hand, in the hydrotreating, especially hydrodesulfurization and hydrodenitrogenation, it is important that the catalyst has desired solid acidity, and it is known that the acidity may be controlled by the silica content of a carrier. Also in this invention, an excessive silica content of a silica/alumina or silica/alumina-containing carrier causes undesirable reactions such as increased consumption of hydrogen or coke formation due to excessive cracking reactions in the hydrodesulfurization or hydrodenitrogenation. Accordingly, in this invention, the silica content of a silica/alumina or silica/alumina-containing carrier is within the range of 2 to 35 percent by weight, preferably 5 to 30 percent by weight, particularly preferably 7 to 12 percent by weight. The inventors of this invention have further discovered that the size distribution of pores in the region of both micropores and macropores of a catalyst greatly influences desulfurization and denitrogenation. Namely, a further feature of this invention has been the finding that a catalyst which preferably has the following properties with respect to the pore size distribution can exhibit an extremely marked desulfurization effect: (1) the volume of pores having a diameter in the range of 30 to 100 Angstroms (3 to 10 nm) is at least 70 percent, preferably more than 80 percent, and most preferably more than 90 percent of the volume of pores having a diameter in the range of 0 to 150 Anstroms (0 to 15 nm); (2) the volume of pores having a diameter in the range of 100 to 300 Angstroms (10 to 30 nm) is less than 30 percent, and preferably less than about 20 percent of the volume of pores having a diameter in the range of 0 to 300 Angstroms (0 to 30 nm) the pore volumes in (1) and (2) being determined according to the nitrogen adsorption method); (3) the volume of pores having a diameter in the range of 150 to 150,000 Angstrom (15 to 15,000 nm) as measured by the mercury porosimetry is 0.005 to 0.25 ml/g, preferably 0.01 to 0.20 ml/g, and most preferably 0.02 to 0.10 ml/g; (4) the volume of pores having a diameter in the range of 300 to 15,000 Angstroms (30 to 1,500 nm) as measured by the mercury porosimetry is less than 0.05 ml/g, preferably less than 0.03 ml/g, and most preferably less than 0.02 ml/g; (5) the volume of pores having a diameter in the range of 150 to 2,000 Angstroms (15 to 200 nm) as measured by the mercury porosimetry is less than about 0.01 ml/g; (6) the volume of pores having a diameter in the range of 0 to 600 Angstroms (0 to 60 nm) as measured by the nitrogen adsorption method is in the range of 0.30 to 0.70 ml/g, preferably 0.40 to 0.65 ml/g, and most preferably 0.45 to 0.60 ml/g; and (7) the specific surface area is in the range from 200 to 400 m²/g, preferably 230 to 350 m²/g, and most preferably 250 to 330 m²/g. Further, the catalyst has a total pore volume of about 0.4 to 0.9 ml/g, a bulk density of about 0.5 to 1.0 g/ml, and a side crushing strength of about 0.8 to 3.5 kg/mm. According to another embodiment of this invention, the following properties are also fulfilled: (8) the volume of pores having a diameter in the range of 150 to 300 Angstroms (15 to 30 nm) corresponds to at most 30 percent, preferably at most 20 percent, and most preferably at most 10 percent of those having a diameter in the range of 0 to 300 Anstroms (0 to 30 nm); and (9) the volume of pores having a diameter in the range of 0 to 300 Angstroms (0 to 30 nm) as measured by the nitrogen adsorption method is in the range of 0.30 to 0.70 ml/g, preferably 0.04 to 0.65 ml/g and most preferably 0.45 to 0.60 ml/g. Accordingly, this invention provides for a hydrotreating catalyst and a method for its preparation, this catalyst comprising a silica/alumina or silica/alumina-containing carrier containing 2 to 35 percent by weight of silica to support a hydrogenation-active component comprising at least one metal selected from the Group VIII metals of the Periodic Table of Elements and at least one metal selected from the Group VIB metals of the Periodic Table of Elements and mixtures thereof and in which the pore structure of the catalyst preferably has the pore size distribution as hereinabove described. In brief, in order to prevent the asphalt and resinous matter contained in a heavy hydrocarbon oil, especially in a residual oil, from penetrating into the pores of a hydrofining catalyst and causing deactivation of the catalyst in performing contact with hydrogen in the presence of said catalyst it is necessary to reduce the pore volume of the macropores. Further, it will be understood that in order to inhibit the conversion of hydrocarbon oil into light hydrocarbons by the carbon-carbon cleavage in saturated hydrocarbons, and to prevent pores from being blocked by asphalt and resinous matter, it is desirable to reduce the volume of pores having a diameter less than 30 Angstroms (3 nm). It is already well known that a solid acid such as alumina/silica is a catalyst component suitable for the desulfurization and denitrogenation reactions of hydrocarbon oils and, as mentioned earlier, it is important in hydrofining that the desired solid activity is retained, and the control of this acidity for this purpose may be made by adjusting the silica content. The inventors of this invention have recognized that the performance and selectivity of a catalyst in the hydrogenation reaction of hydrocarbons may be controlled by specifying the pore structure of the catalyst and at the same time adjusting the cracking activity by controlling the acidity by the silica content of the carrier. The selectivity of this kind plays an extremely important role because it is effective in saving hydrogen consumption and preventing the deactivation of a catalyst due to the deposition of carbon produced in the cracking reactions in carrying out the desulfurization and denitrogenation of hydrocarbon oils. Therefore, as mentioned above, in order to prevent an increase in hydrogen consumption, coke formation, etc., caused by excessive cracking reaction, in the hydrodesulfurization reaction or the hydrodenitrogenation reaction, the silica content of an alumina-containing carrier should be within the range of 2 to 35 , preferably about 5 to 30 and most preferably about 7 to 12 percent by weight. In the above-mentioned hydrotreating catalyst, the pore diameters fall mostly in the range of 30 to 100 Angstroms (3 to 10 nm) as measured by the nitrogen adsorption method, but as a whole, these pores are distributed over a relatively wide range. The reason why the pore size distribution of the catalyst disclosed in this invention exerts a marked effect on the activity and activity maintenance in the hydrodesulfurization of hydrocarbon oil will be as follows, though it is not fully understood. Because the pore size distribution is relatively wide, asphalt, resinous matter and metal-containing compounds in a feedstock are attached to the surface of the catalyst to block the pores and isolate the active sites of the catalyst completely when these pores are extremely small, while when the pore size is large in a specified range, the metal-containing components, i.e., asphalt or resin, are attached suitably to the surface of a catalyst but do not block the pores completely, which permits the access of hydrocarbon molecules and sulfur molecules reaching the catalyst to the active sites to thereby exert a high performance. The carrier which is used in a preferred embodiment of this invention is an alumina or alumina-containing substance containing 2 to 35 percent by weight of silica. The alumina-containing substance is a composition obtained by mixing alumina with a different carrier material, and it is possible to add at least one member selected from the group consisting of, for example, magnesia, calcium oxide, zirconia, titania, boria, hafnia, and crystalline zeolite to alumina. As mentioned above, said silica is suitable for controlling the solid acidity of the catalyst, so that it may be used in an amount in the range of 2 to 35 percent by weight, preferably about 5 to 30 percent by weight, based on the carrier. A particularly preferable silica content may be in the range of about 7 to 12 percent by weight. This silica gives strong-acid sites to the catalyst and enhances the cracking activity of the catalyst, whereas magnesia, for example, has an effect of decreasing the strong-acid sites contained in alumina/silica or the like, and at the same time, increasing the weak-acid sites to improve the selectivity of the catalyst. The amounts of addition of the above-mentioned refractory inorganic oxides such as magnesia, calcium oxide, zirconia, titania, boria, hafnia and a crystalline zeolite are suitably 1 to 10 percent by weight, based on the alumina/silica. Suitable alumina includes γ-alumina, χ-alumina, η-alumina, and a mixture thereof, though any alumina that can provide the pore size distribution and the properties disclosed in this invention can be used desirably. Processes which can be adopted in producing the alumina-silica include one comprising separately preparing alumina and silica gels and blending them, one comprising immersing silica gel in a solution of an aluminum compound and precipitating alumina gel on the silica gel by adding a suitable amount of a basic substance, and one comprising coprecipitating a water soluble aluminum compound and a water-soluble silicon compound by adding a basic substance to a uniform solution of both compounds. In order to obtain a catalyst having a pore size distribution and properties necessary for the hydrotreatment catalyst used in this invention, conditions including a temperature of 60 to 90°C and a time of 0.5 to 3 hours are necessary in the preparation and aging of aluminum and silica hydrates. Specific materials which can be used in obtaining the catalyst having the desired pore size distribution and properties include, for example, water-soluble acidic aluminum compounds and water-soluble alkaline aluminum compounds, and specifically, sulfates, chlorides, and nitrates of aluminum, alkali metal aluminates, aluminum alkoxides, and other inorganic or organic salts. Suitable water-soluble silicon compounds include silicon-containing compounds such as alkali metal silicates (preferably one having a Na₂O to SiO₂ ratio of 1:2 to 1:4), tetraalkoxysilanes, and orthosilicate esters. These aluminum and silicon compounds may be used in the form of aqueous solutions, and the concentrations of the aqueous solutions are not particularly limited but are suitably selected without any objection and the concentration of an aqueous aluminum compound solution may be selected in the range of about 0.1 to 4.0 molar. An embodiment of the process for producing an alumina/silica carrier suitable for use in the hydrotreatment catalyst of this invention will follow. An aqueous solution of an acidic aluminum solution and an alkali hydroxide are added to hot water at about 50 to 98°C and the resulting solution is adjusted to have a pH in the range of about 6.0 to 11.0, preferably about 8.0 to 10.0, and allowed to stand for at least one hour at a temperature of about 50 to 98°C. This solution is further kept at a temperature of about 50 to 98°C for at least two hours, during which an aqueous solution of an alkali silicate and, if necessary, a mineral acid solution are added to adjust the pH to a value in the range of about 8.0 to 10.0. When a hydroxycarboxylic acid or its salt, for example, tartaric acid, citric acid, or other hydroxypolycarboxylic acids or their alkali metal salts are added, a still better catalyst carrier can be obtained. Further, an aminodicarboxylic or its salt, for example, glutamic acid, aspartic acid, or other amino group-containing polycarboxylic acid or their alkali metal salts can be used. These compounds can be added in an amount in the range of 0.0002 to 0.1 mole per mole of an aluminum compound. After completion of this treatment, the precipitate is filtered, washed with an ammonium acetate or an ammonium carbonate solution and water to remove ionic impurities, and dried and calcined into a finished carrier by the usual methods. This drying is performed by heating to a drying temperature of about 200°C in the presence or absence of oxygen, and the calcination is performed by heating to a temperature in the range of about 200 to 800°C in the presence of oxygen. The hydrogenation-active metal components supported on the carrier are at least one metal selected from the group consisting of Group VIB and at least one metal selected from the group consisting of Group VIII metals of the Periodic Table of Elements. Namely, at least one metal is selected from the group consisting of Group VIB metals including chromium, molybdenum, and tungsten, and Group VIII metals including iron, cobalt, nickel, palladium, platinum, osmium, iridium, ruthenium and rhodium for use. Preferably molybdenum and tungsten, as Group VIB metals, may be used alone or together. Similarly, preferred Group VIII metals include cobalt and nickel which may be used alone or together. Particularly, in the hydrodesulfurization of hydrocarbon oil, a combination of a Group VIB metal with a Group VIII metal, for example, molybdenum/cobalt, molybdenum/nickel, tungsten/nickel, molybdenum/cobalt/nickel, or tungsten/cobalt/nickel may be used suitably. It is also possible to add a Group VII metal in the Periodic Table of Elements, for example, manganese, or a Group IV metal, for example, tin or germanium to these active metal components. These hydrogenation-active metal components are suitably supported in the form of oxides and/or sulfides. The process for supporting includes an impregnation process comprising immersing a carrier in a solution of a soluble salt of said metal to thereby infiltrate the metal component into the carrier and a coprecipitation process in which the metal components are precipitated simultaneously during the production of the carrier, and any other processes may be used without any obstruction, among which the impregnation process is preferred to secure the operation and catalytic performances. The impregnation is performed by immersing a carrier in an impregnation solution at room temperature or higher and holding this carrier under such a condition as to permit the carrier to be impregnated fully with the desired components. The amount and temperature of the impregnation solution may be suitably adjusted so that the desired amount of the metals may be supported. The amount of the carrier which is to be immersed in the impregnation solution is determined depending on the amount of metals supported. As has been mentioned above, the preferred procedure for supporting the hydrogenation-active metal components is via a novel two-step impregnation procedure wherein in a first step a carrier is immersed in aqueous solutions of soluble salts of at least one Group VIII metal and then in a subsequent second impregnation step the Group VIII metal impregnated carrier from said first step is immersed in aqueous solutions of soluble salts of at least one Group VIB metal to thereby introduce the metal components into the carrier. The impregnation operation comprises immersing a carrier in an impregnation solution at ordinary temperature or higher and holding the carrier under such a condition as to permit full impregnation of the carrier with the desired components. The amount and temperature of the impregnation solution may be suitably selected so that the metals may be supported in desired amounts. The amount of the carrier immersed in an impregnation solution is determined by the amount of metals to be supported. The hydrogenation-active metal component which is supported by a carrier in the first step is at least one metal selected from the group consisting of Group VIII metals of the Periodic Table of Elements. Namely, at least one member is selected from the Group VIII metals including iron, cobalt, nickel, palladium, platinum, osmium, iridium, ruthenium, and rhodium. Preferably, cobalt and nickel may be used alone or together. The hydrogenation-active metal component which is supported by a carrier in the second step is at least one metal selected from the group consisting of Group VIB metals of the Periodic Table of Elements. Namely, at least one member is selected from the Group VIB metals including chromium, molybdenum and tungsten. Preferably, molybdenum and tungsten may be used alone or together. As previously mentioned, a third metal, if desired, may be added in the pretreatment of the carrier prior to the first step or in the aftertreatment after the second step. The inventors of this invention have found that a most suitable means for carrying out the first step in the process for producing a catalyst according to this invention is an ion exchange process wherein the exchange between the protons on the surface of a silica/alumina or silica/alumina-containing carrier and said metal ions is performed through ammonium ions. It has been found that when this invention is performed according to the ion exchange process, the dispersibility in a catalyst is improved markedly as compared with that in a catalyst prepared by a usual impregnation process, and the chemical uniformity can also be improved. Further it has been found that in the case of allowing a silica/alumina carrier or a silica/alumina-containing carrier to support a Group VIII metal by the ion-exchange method, the catalyst prepared by such method is subject to less influence of the calcination temperature during a calcination step due to the increasing dispersibility and chemical uniformity in said supporting step as mentioned above. The process for producing the catalyst according to the ion-exchange method is performed by preparing a solution of basic complex salt such as a solution of an ammine complex salt or an amine complex salt of the active metal and immersing a silica/alumina carrier or a silica/alumina-containing carrier in said solution to thereby allow the carrier to support said metal. The amount and concentration of the solution of the basic complex salt may be suitably controlled so that the desired amount of the metal may be supported. The hydrogenation-active metal components of Groups VIII and VIB are supported suitably in the form of an oxide and/or a sulfide. The amounts of the active metal components supported are 0.5 to 20 percent by weight, preferably 1 to 8 percent by weight, particularly preferably 2 to 5 percent by weight in terms of an oxide, based on the catalyst, for a Group VIII metal, and 5 to 30 percent by weight, preferably 8 to 25 percent by weight, and particularly preferably 12 to 20 percent by weight, in terms of an oxide, based on the catalyst for a Group VIB metal. When the amount of a Group VIII metal supported is below 0.5 percent by weight, no satisfactory catalyst can be obtained, while when it exceeds 20 percent by weight, the amount of a free metal component not bound with a carrier increases. When the amount of a free component of a Group VIII metal is increased, an inactive double oxide is formed in the subsequent step of allowing a carrier to support a Group VIB metal, which lowers the dispersibility of the Group VIB metal to thereby lower the catalytic activity. On the other hand, when the amount of a Group VIB metal is below 5 percent by weight, no sufficient activity can be obtained, while when it exceeds 30 percent by weight, the dispersibility is lowered and besides no effect of a Group VIII metal as a promoter is obtained. The form of the catalyst may be cylinders, granules, tablets, or any other shapes, and these shapes can be obtained by molding processes such as extrusion and granulation. The diameter of the extrudate is preferably in the range of 0.5 to 3.0 mm. The carrier impregnated with the hydrogenation-active metal components is separated from the impregnation solution, dried, and calcined. The drying may be carried out by heating up to a temperature of about 200°C in the presence or absence of oxygen, and the calcination is performed by heating to a temperature in the range of 200°C to 800°C in the presence of oxygen. As mentioned above, the catalyst produced in this way comprises a silica/alumina or silica/alumina-containing carrier containing 2 to 35 percent by weight of silica and supporting at least one kind of a hydrogenation-active metal component and is characterized in that: (1) the volume of pores having a diameter in the range of 30 to 100 Angstroms (3 to 10 nm) is at least 70 percent, preferably more than 80 percent and most preferably more than 90 percent of the volume of pores having a diameter in the range of 0 to 150 Angstroms (0 to 15 nm), (2) the volume of pores having a diameter in the range of 100 to 300 Angstroms is less than 30 percent and preferably less than about 20 percent of the volume of pores having a diameter in the range of 0 to 300 Angstroms (0 to 36 nm)( the pore volumes in (1) and (2) being determined according to the nitrogen adsorption method), (3) the volume of pores having a diameter in the range of 150 to 150,000 Angstroms (15 to 15,000 nm) as measured by the mercury porosimetry is 0.005 to 0.25 ml/g, preferably 0.01 to 0.20 ml/g and most preferably 0.02 to 0.10 ml/g, (4) the volume of pores having a diameter in the range of 300 to 15,000 Angstroms (30 to 1,500 nm) as measured by the mercury porosimetry is less than 0.05 ml/g, preferably less than 0.03 ml/g and most preferably less than 0.02 ml/g, (5) the volume of pores having a diameter in the range of 150 to 2,000 Angstroms (15 to 200 nm) as measured by the mercury porosimetry is less than 0.01 ml/g, (6) the volume of pores having a diameter in the range of 0 to 600 Angstroms (0 to 60 nm) as measured by the nitrogen adsorption method is in the range of 0.30 to 0.70 ml/g, preferably 0.40 to 0.65 ml/g and most preferably 0.45 to 0.60 ml/g and (7) the specific surface area is in the range from 200 to 400 m²/g, preferably 230 to 350 m²/g and most preferably 250 to 330 m²/g. Further it has a total pore volume of 0.5 to 1.0 ml/g, a bulk density of about 0.5 to 1.0 g/ml, a side crushing strength of about 0.8 to 3.5 kg/mm; and realizes an excellent catalyst for hydrotreating hydrocarbon oil. The nitrogen adsorption method and the mercury porosimetry which are used as methods for measuring the pore volume of a catalyst are performed in accordance with the methods described in P. H. Emmett, et al; Catalysis 1 ,123 (1954) (Reinhold Publishing Co.) and Lectures on Catalyst Engineering (Shokukai Kogaku Koza) Vol. 4, Pages 69 to 78 (1964) (Chijinshokan). The mercury porosimetry is performed on the assumption that the angle of a catalyst with mercury is 140°, the surface tension is 480 dynes/cm (0.4896g/cm), and the pores are all cylindrical. For the nitrogen adsorption method, a number of methods are proposed for correcting multilayer adsorption. Among these, BJH method [E. P. Barrett, L. G. Joyner and P. P. Halanda; J. Amer. Chem. Soc., 73 , 373 (1951)], and CI method [R. W. Cranston and F. A. Inkley; "Advances in Catalysis", IX , 143 (1957) (New York Academic Press)] are usually used. The data on pore volumes in this invention are those obtained by using the adsorption sides of adsorption isothermic curves and calculating the volume according to the DH method [D. Dollimore and G. R. Heal; J. Applied Chem., 14 , 109 (1964)] Description will be made of a process for hydrodesulfurizing hydrocarbon oils by using a catalyst produced according to this invention. Vacuum gas oils, heavy cracked gas oils and atmospheric gas oils are examples of oils which can be used as the hydrocarbon feedstocks for the hydrotreating of this invention. A vacuum gas oil is heavy distillate containing considerable amounts of sulfur, nitrogen compounds and metal compounds obtained by subjecting an atmospheric residual oil to vacuum distillation and containing a fraction having a boiling point in the range of about 250 to about 560°C. For example, a vacuum gas oil obtained from Middle East crude oil contains about 2 to 4 percent by weight of sulfur, about 0.05 to 0.2 percent by weight of nitrogen, and about 0.4 to 0.5 percent by weight of Conradson carbon residue. A heavy cracked oil is an oil having a boiling point higher than about 200°C, obtained by thermal cracking of a residual oil. For example, distillates obtained by the coking or vis-breaking of residual oils can be used. Further, as hydrocarbon oil feedstocks, heavy hydrocarbon oils including residual oils obtained by atmospheric or vacuum distillation of crude oils can be employed. For example, a residual oil containing about 30 to 100 percent by weight of a hydrocarbon component having an atmospheric boiling point higher that about 480°C usually contains about 1 to 10 percent by weight of nitrogen, about 10 to 1,000 ppm of metals and about 1 percent by weight of Conradson carbon residue. The above-mentioned atmospheric gas oils, atmospheric residual oils, vacuum gas oils, vacuum residual oils, and heavy cracked oils, and mixtures thereof may be used as feedstocks to the hydrotreating of this invention. Reaction conditions may be selected appropriately depending upon the kind of feedstocks, desulfurization or denitrogenation percentages, and the like. Specifically, the reaction is generally conducted under the following conditions: a reaction temperature of about 350 to 450°C, a reaction pressure of about 30 to 200 kg/cm² (2942 to 19613 kPa), a hydrogen-containing gas flow rate of about 50 to 1,500 l/l. and a liquid hourly space velocity of about 0.2 to 2.0 V/H/V are adopted. The hydrogen concentration of hydrogen-containing gas may be in the range of about 60 to 100 percent. The catalyst which is produced according to this invention is characterized that deactivation is very low and a high degree of desulfurization can be attained even under mild reaction conditions, especially, at a low reaction pressure. It is preferred that the catalyst is presulfided prior to its use. This presulfiding may be performed in situ, namely in a reactor. Namely, a calcined catalyst is brought into contact with a sulfur-containing distillate in the presence of about 50 to 1,500 l/l of a hydrogen-containing gas under conditions including a temperature of about 150 to 400°C, a pressure (total pressure) of about 5 to 100 kg/cm² (490 to 9807 kPa)and a liquid hourly space velocity of about 0.3 to 2.0 V/H/V. After this sulfiding treatment, the sulfur-containing distillate is switched over to a feedstock, and the operation is restarted under operation conditions suitable for desulfurization of the feedstock. In addition to the above process, use may be made of a process for effecting sulfiding comprising either bringing the catalyst into direct contact with hydrogen sulfide or other sulfur compounds or by adding the sulfur compound to a suitable distillate and bringing the resulting distillate into contact with the catalyst. Although the catalyst may be used in any of the systems including fixed bed, fluidized bed, and moving bed, a fixed bed reactor is preferred in performing hydrodesulfurization from the viewpoint of apparatus and operation. Further, it is also possible to obtain a high degree of desulfurization by performing hydrodesulfurization by using a plurality of reactors connected. Further, the catalyst of this invention may be packed for use in a guard drum for demetallization provided in front of the main reactor chiefly for desulfurization/denitrogenation reactions. This invention will now be described with reference to examples. Example 1 4.0 ℓ of deionized water was heated to about 70°C. To this were added an aqueous sodium hydroxide solution (231.5 g of NaOH in 578.8 g of deionized water] and an aqueous aluminum sulfate solution (649.4 g of aluminum sulfate in 994.5 g of deionized water), and the resulting solution was aged at about 70°C for about two hours, during which its pH was being adjusted to a value of 8.8 to 9.2 with a sodium hydroxide solution or a nitric acid solution. To this was added a sodium silicate solution (32.4 g of No. 3 water glass in 98.6 g of deionized water) and the resulting solution was aged at a temperature of about 70°C for 3 hours, during which its pH was being adjusted to about 9 with a nitric acid solution when necessary. The formed slurry was filtered, and the filtered cake was reslurried in a 1.5 percent ammonium carbonate solution, filtered, and washed with an ammonium carbonate solution until the sodium concentration of the filtrate was lowered to below 5 ppm. This was dried at 100°C for 16 hours and, after adding deionized water and a small amount of acetic acid, simultaneously dried and mixed until the mixture attained a moldable water content and molded into a cylinder of 1.56 mm diameter by an extruder. The molded pellets were dried at 100°C for 16 hours, and further calcined at 600°C for 3 hours to form a carrier. This carrier was impregnated with an aqueous solution of a molybdenum salt in an amount sufficient to provide a final metal content of molybdenum of about 15 percent (in terms of an oxide) and then dried and calcined. Then, this carrier was impregnated with an aqueous solution of a cobalt salt in an amount sufficient to provide a final metal content of molybdenum of about 5 percent (in terms of an oxide) and dried and calcined to form a catalyst. The physical properties and chemical composition of the catalyst are shown in Table 1. Example 2 4.0 ℓ of deionized water was heated to about 70°C. To this were added an aqueous caustic soda solution (230.2 g of NaOH in 575.5 g of deionized water) and an aluminum sulfate solution (649.4 g of aluminum sulfate in 960.6 g of deionized water). The resulting solution was aged at about 70°C for two hours, during which the pH was being adjusted to 8.8 to 9.0 with a sodium hydroxide solution or a nitric acid solution. To this a sodium silicate solution (34.7 g of No. 3 water glass in 114.3 g of deionized water) was added, and aged at about 70°C for 3 hours, during which the pH was maintained at about 9 by adding a nitric acid solution when necessary. The subsequent procedures were the same as in Example 1. The properties of the formed catalyst are shown in Table 1. Example 3 4.0 ℓ of deionized water was heated to about 70°C. To this were added an aqueous caustic soda solution (232.0 g of NaOH in 580.0g of deionized water) and an aluminum sulfate solution (640.0 g of aluminum sulfate in 991.0 g of deionized water and 3.3 g of ammonium tartrate). The resulting solution was aged at about 70°C for two hours, during which the pH was maintained at 8.8 to 9.0 with a nitric acid solution. To this was added a sodium silicate solution (79.7 g of No. 3 water glass in 179.1 cm³ of deionized water) and the resulting solution was aged at about 70°C for 3 hours, during which the pH was maintained at about 9 by adding a nitric acid solution when necessary. The subsequent procedures were the same as in Example 1. The properties of the formed catalyst are shown in Table 1. Comparative Example A Comparative Example was carried out in the same manner as in Example 1, except that no sodium silicate solution was added. The properties of the formed catalyst are shown in Table 1. Effect of the Invention The hydrotreatment of a kerosene fraction was carried out by using each of the catalysts of Example 1 and Comparative Example. The reaction conditions were as follows: The hydrotreatment of a feed oil comprising an atmospheric gas oil fraction of Mideast crude petroleum was carried out by using the catalyst of Example 2 and Comparative Example under the following reaction conditions: As will be understood from the comparison test, the hydrotreatment catalyst according to this invention can provide good desulfurization and denitrogenation rates because of its specified pore size distribution. Namely, the catalyst according to this invention has excellent activity and activity retentivity and is effective in efficiently performing the hydrotreatment of hydrocarbon oil. Examples 4, 5 and 6 13.9 g of cobalt nitrate was dissolved in 70 ml of distilled water. 80 ml of ammonia was added thereto to obtain a cobalt ammine complex salt solution. 50 g of a silica/alumina carrier (silica content of 10 percent by weight) was immersed in this solution for 16 hours to allow it to support 5 percent by weight (in terms of an oxide) of cobalt. A catalyst obtained by air-drying and calcination at 300°C is referred to as catalyst A (Example 4), a catalyst obtained by calcination at 500°C as catalyst B (Example 5), and a catalyst obtained by calcination at 600°C as catalyst C (Example 6). Examples 7 and 8 (Comparative) A commercially available alumina carrier was allowed to support 5 percent by weight (in terms of cobalt oxide) of cobalt in the same procedure as in Example 4. A catalyst prepared at a calcination temperature of 300°C is referred to as catalyst D (Example 7), and a catalyst prepared at a calcination temperature of 600°C as catalyst E (Example 8). To see the state of cobalt oxide on the carrier, the catalysts obtained in Examples 4, 5, 6, 7 and 8 were analyzed by the temperature-programmed reduction method. The procedure was in accordance with that by J. W. Jenkins et al (CHEMTECH Vol. 7, 316-320 (1977)). The results are shown in Figures 1 through 5. The cobalt oxide supported on the alumina carrier is either in a state in which it is reducible at below 300°C (this is thought to exist in the form of fine cobalt oxide particles not bound with the carrier) or in a state in which it is not reducible at 700°C (this is thought to be a cobalt oxide which is bound strongly with alumina, such as cobalt aluminate). In catalyst D prepared at a calcination temperature of 300°C, the cobalt oxide mostly takes the form of the former, while in catalyst E prepared at a calcination temperature of 600°C, the cobalt oxide mostly takes the form of the latter. For catalysts prepared at intermediate temperatures, only the ratio of both was varied, and no cobalt oxides in other forms were found. On the other hand, on the silica/alumina carrier, the amounts of cobalt oxides in the states observed on the alumina carrier are rather small and a cobalt oxide reducible at 500 to 700°C (a cobalt oxide moderately bound with a carrier) accounts for a major portion. Thus the influence of the calcination temperature is smaller than that in the alumina carrier. The above results indicate that there is a marked difference in respect of the state of a cobalt oxide which is one of the active metal components between the silica/alumina carrier and alumina which is widely used as a carrier for desulfurization catalysts, and therefore suggest that the use of the silica/alumina carrier makes a novel catalyst manufacturing process having this merit possible. Example 9 The same silica/alumina carrier as in Example 4 was allowed to support 5.0 percent by weight of cobalt in the form of a cobalt oxide in the same procedure as in Example 4 except that an aqueous cobalt nitrate solution was used instead of the solution of cobalt ammine complex salt. The catalyst prepared at a calcination temperature of 500°C is referred to as catalyst F. The results of analysis by the temperature-programmed reduction method of catalyst F are shown in Figure 6. As compared with catalyst B, this catalyst showed a somewhat complicated profile, which indicated that the state of the oxide supported was not uniform. Comparative Examples 1, 2, 3 and 4 Four kinds of cobalt/molybdenum catalysts were produced by using a silica/alumina containing 25 percent by weight of silica as a carrier. Catalyst G (Comparative Example 1) 13.2 g of ammonium molybdate was dissolved in 50 ml of 3N-aqueous ammonia. 25 g of a silica/alumina carrier was immersed in this solution, then allowed to stand for two hours and, after discarding the liquid, dried in air. After calcination at 550°C, this carrier was allowed to support cobalt in the same procedure as in Example 9. After air-drying, the product was calcined at 550°C to obtain catalyst G. Catalyst H (Comparative Example 2) A carrier was allowed to support molybdenum by the same procedure as in the production of catalyst G, then calcined at 550°C, and further allowed to support cobalt by using a solution of cobalt ammine complex salt by the same procedure as in Example 4. After air-drying, the carrier was calcined at 550°C to obtain catalyst H. Catalyst I (Comparative Example 3) 13.9 g of cobalt nitrate was dissolved in 70 ml of distilled water. To this solution, 80 ml of ammonia was added. 26.4 g of ammonium molybdate was further dissolved in this solution. 50 g of a silica-alumina carrier was immersed in this solution, allowed to stand for two hours and, after discarding the liquid and air-drying, calcined at 550°C to obtain catalyst I. Catalyst J (Comparative Example 4) 28.0 g of phosphomolybdic acid was dissolved in 150 ml of ethanol. 27.7 g of cobalt nitrate was dissolved in this solution. 50 g of a silica/alumina carrier was immersed in the resulting solution, allowed to stand for two hours and, after discarding the liquid, dried in air and calcined at 550°C to obtain catalyst J. Examples 10 and 11 Catalyst K (Example 10) A carrier was allowed to support cobalt by the same procedure as in Example 4 by using a solution of cobalt amine complex salt. After air-drying, the carrier was calcined at 550°C and then immersed in a 3N-aqueous ammonia solution of ammonium molybdate to allow it to support molybdenum. After air-drying, the carrier was calcined at 550°C to obtain catalyst K. Catalyst L (Example 11) A carrier was allowed to support cobalt in the same procedure as in Example 7 by using an aqueous solution of cobalt nitrate. After air-drying, the carrier was calcined at 550°C, and further allowed to support molybdenum in the same way as in Example 10 to obtain catalyst L. The desulfurization activities of catalysts G, H, I, J, K, and L were examined by the desulfurization reaction of thiophene. The feed had a composition of 5.5 percent by weight of thiophene, 2.3 percent by weight of pyridine, and 92.2 percent by weight of n-hexane. The reaction conditions were as follows: The above results show that with an alumina carrier containing silica, catalysts K and L of this invention had markedly high activities as compared with catalysts G, H, I, and J which were prepared by other methods. Comparative Examples 5 and 6 , and Examples 12 through 18 Nickel/molybdenum catalysts (M through U) were prepared by using nine kinds of silica/alumina carriers having different silica contents. The supporting procedure used was the same as in Example 10 (catalyst K) except that a nickel amine complex salt was used. The performances of these catalysts were evaluated by the desulfurization reaction of a vacuum distillate from Middle East crude oil. The reaction conditions were as follows: The results of Table 3 shows that the manufacturing process according to this invention shows a marked effect of improving the desulfurization and/or denitrogenation activities of a cobalt/molybdenum or nickel/molybdenum catalyst prepared from a silica/alumina carrier containing 2 to 35 percent by weight of silica. Example 19 9.7 g of cobalt nitrate and 1.4 g of nickel nitrate were dissolved in 70 ml of distilled water. Then, 50 g of a silica/alumina carrier containing 10 percent by weight of silica was immersed in this solution for 12 hours, and allowed to support cobalt and nickel in the form of oxides in an amount of 3.5 percent by weight and 0.5 percent by weight, respectively. This carrier supporting cobalt and nickel was dried in air, calcined at 550°C, and immersed in a 3N-aqueous ammonia molybdate solution to obtain a catalyst supporting 14 percent by weight of molybdenum in the form of molybdenum oxide (catalyst V). The results are shown in Table 4. This table shows that the Co-Ni-Mo catalyst according to this invention also showed excellent desulfurization and denitrogenation rates. Example 20 Catalyst W was prepared by using the same conditions and procedure as in Example 14, except that wolfram was used instead of molybdenum. Tungsten was supported by a carrier by using a solution of ammonium tungstate in distilled water. The results on catalyst W are shown in Table 4. This table shows that the Ni/W catalyst according to this invention also showed excellent desulfurization and denitrogenation activities. Example 21 4.8 ℓ of distilled water was heated to about 70°C. To this were added a sodium hydroxide solution (233.6 g of deionized water) and an aqueous aluminum sulfate solution (644.5 g of aluminum sulfate and 987 g of deionized water). To the resulting solution was added an aqueous diammonium tartrate solution in an amount such that 2 moles of diammonium tartrate was present per 1 mole of alumina. The pH of this solution was adjusted to 8.8 to 9.2 with a sodium hydroxide solution or an aqueous nitric acid solution, and then aged at about 70°C for about one hour. To this an aqueous sodium silicate solution (42.5 g of No. 3 water glass, 129.4 g of deionized water) was added and, if desired, an aqueous nitric acid solution was added to adjust the pH to about 9. The resulting solution was aged at a temperature of about 70°C for three hours. The produced slurry was filtered, and the cake was reslurried in a 1.5 percent ammonium carbonate solution, then filtered and washed with an ammonium carbonate solution until the sodium concentration of the filtrate was lowered to below 5 ppm. It was dried at 100°C for 16 hours, and after adding deionized water and a small amount of acetic acid, mixed while it was being dried to a moldable water content, and then molded through an extruder into a cylinder of 1.5 mm . The molded pellets were dried at 100°C for 16 hours and further calcined at 600°C for three hours to obtain a carrier. Separately, the carrier was allowed to support nickel and molybdenum by using the same procedure as in Example 14 except that use was made of a nickel amine complex salt solution prepared by dissolving nickel nitrate in distilled water and adding thereto ammonia. Namely, 50 g of the above silica/alumina carrier (silica content of 10 percent by weight) was immersed in this nickel amine complex salt solution for 16 hours to allow the carrier to support 4 percent by weight of nickel in the form of a nickel oxide. This carrier supporting nickel was dried in air, calcined at 550°C, and allowed to support 14 percent by weight of molybdenum in the form of molybdenum oxide by immersing in a 3N-aqueous ammonium molybdate solution. After air-drying, it was calcined at 550°C to obtain a catalyst. This is referred to as catalyst X. The physical properties of this catalyst are as follows: Physical Properties: Catalysts N through T in Examples 12 through 18 were prepared by using tentatively produced silica/alumina carriers and, for example, catalyst P (Example 14) having a silica content of 10 percent by weight had the following physical properties. Physical Properties: Table 4 shows that catalyst X having a specified pore size distribution had more excellent desulfurization and denitrogenation rates than catalyst P hating a different pore size distribution. Example 22 9.8 g of cobalt nitrate and 1.4 g of nickel nitrate were dissolved in 70 ml of distilled water, to which was further added 80 ml of ammonia to obtain a mixed cobalt/nickel ammine complex salt solution. 50 g of a silica/alumina carrier containing 10 percent by weight of silica was immersed in this solution for 16 hours to allow the carrier to support cobalt and nickel in the form of oxides in amounts of 3.5 percent by weight and 0.5 percent by weight, respectively. After air-drying and calcination, it was allowed to support molybdenum in the form of an oxide in an amount of 14 percent by weight in the same manner as in Example 21 to obtain catalyst Y. Examples 23 through 29, Comparative Examples 7 through 10 The relationship between the amount of the hydrogenation-active metals supported and catalyst activity was investigated by varying the amount of the hydrogenation-active metals supported. The results are shown in Table 5. Table 5 shows that the effective amount of a Group VIII metal was 0.5 to 20 percent by weight and that of a Group VIB metal was 5 to 30 percent by weight. Example 30 Atmospheric gas oil fraction of Middle East Crude oil was used as a feed stock, and its hydrotreating was carried out by using catalyst Y or V under the following reaction conditions, with good results. Reaction conditions: Feed oil properties: Brief Description of the Drawings Figs. 1 through 3 are graphs each illustrating the analytical results obtained by the temperature-programmed reduction method to observe the state of cobalt oxides supported by a silica/alumina carrier subjected to the first step treatment by an ion exchange method according to the process of this invention. Figs. 4 and 5 are graphs each illustrating the analytical results obtained by the temperature-programmed reduction method to observe the state of cobalt oxides supported on a catalyst prepared by allowing an alumina carrier to support cobalt by an ion exchange method. Fig. 6 is a graph illustrating the analytical results obtained by the temperature-programmed reduction method to observe the state of cobalt oxides supported on a silica/alumina carrier subjected to the first step treatment by an impregnation method according to this invention.

Claims: A method of preparing a hydrotreating catalyst, said method comprising the following steps in the stated sequence: (a) providing a carrier formed of silica/alumina or a silica/alumina-containing substance, said carrier containing silica in an amount of from 2 to 35% by weight (e.g. from 7 to 12% by weight); (b) thereafter causing said carrier to initially support first at least one metal selected from the group consisting of Group VIII metals of the Periodic Table of the Elements, said selected Group VIII metal being contained in an amount of from 0.5 to 20% (e.g. from 2 to 5%) by weight in terms of an oxide; (c) thereafter causing said carrier containing said Group VIII metal to support at least one metal selected from the group consisting of Group VIB metals of the Periodic Table of the Elements, said selected Group VIB metal being contained in an amount of from 5 to 30% (e.g. from 12 to 20%) by weight in terms of an oxide; and (d) thereafter recovering said hydrotreating catalyst. A method according to claim 1 wherein in the said step (b), said carrier is first immersed in a solution of a salt of at least one of said Group VIII metals so as to obtain an impregnated carrier containing from 0.5 to 20 wt. % (e.g. from 2 to 5 wt. %), based on the oxide, of said Group VIII metal; the resultingly Group VIII metal-containing carrier of step (b) is dried and calcined, and in the said step (c), the said dried and calcined carrier is immersed in a solution of a salt of at least one of said Group VIB metals so as to obtain an impregnated carrier containing from 5 to 30 wt. % (e.g. from 12 to 20 wt. %), based on the oxide, of said Group VIB metal. A method according to claim 2 wherein the said drying step of the impregnated carrier is an air-drying step. A method according to claim 2 or claim 3 wherein the calcination step is effected at temperatures in the range of from 200 to 800°C. A method according to any one of claims 2 to 4 wherein the said solution of a salt in said first impregnation of the carrier in step (b) comprises a basic complex of said salt of said Group VIII metal (e.g. an ammine complex salt or an amine complex salt). A method according to any one of claims 1 to 5 wherein said Group VIII metal is selected from cobalt, nickel and mixtures thereof and said Group VIB metal is selected from molybdenum, tungsten and mixtures thereof. A method according to any one of claims 1 to 6 wherein the hydrotreating catalyst has a specific surface area in the range of from 200 to 400 m²/g (e.g., from 250 to 330 m²/g) and the following pore distribution: (i) the volume of pores having a diameter in the range of from 30 to 100 Å (30 x 10⁻¹⁰ to 100 x 10⁻¹⁰m) is at least 70% (e.g., at least 90%) of the volume of pores having a diameter in the range of from 0 to 150 Å (0 to 150 x 10⁻¹⁰m); (ii) the volume of pores having a diameter in the range of from 100 to 300 Å (100 x 10⁻¹⁰ to 300 x 10⁻¹⁰m) is less than 30% (e.g., less than 20%) of the volume of pores having a diameter in the range of from 0 to 300 Å (0 to 300 x 10⁻¹⁰m) (the pore volume in (i) and (ii) being determined by the nitrogen adsorption method); (iii) the volume of pores having a diameter in the range of from 150 to 150,000 Å (150 x 10⁻¹⁰ to 150,000 x 10⁻¹⁰m) as measured by the mercury porosimetry method is in the range of from 0.005 to 0.25 ml/g (e.g., 0.02 to 0.10 ml/g); (iv) the volume of pores having a diameter in the range of from 300 to 15,000 Å (300 x 10⁻¹⁰ to 15,000 x 10⁻¹⁰m) as measured by the mercury porosimetry method is less than 0.05 ml/g (e.g., less than 0.02 ml/g); (v) the volume of pores having a diameter in the range of from 150 to 2000 Å (150 x 10⁻¹⁰ to 2000 x 10⁻¹⁰m) as measured by the mercury porosimetry method is less than 0.01 ml/g; and (vi) the volume of pores having a diameter in the range of from 0 to 600 Å (0 to 600 x 10⁻¹⁰m) as measured by the nitrogen adsorption method is in the range of from 0.30 to 0.70 ml/g (e.g., 0.45 to 0.60 ml/g). A method according to claim 7 wherein the pore distribution of the hydrotreating catalyst has the following features: (i) the volume of pores having a diameter in the range of from 150 to 300 Å (150 x 10⁻¹⁰m to 300 x 10⁻¹⁰m) corresponds at most to 30% of those having a diameter in the range of from 0 to 300 Å (0 to 300 x 10⁻¹⁰m); (ii) the volume of pores having a diameter in the range of from 0 to 300 Å (0 to 300 x 10⁻¹⁰m) as measured by the nitrogen adsorption method is in the range of from 0.30 to 0.70 ml/g. A method according to any one of claims 1 to 8 wherein the said carrier of step (a) contains from 1 to 10 weight %, based on the alumina and silica content thereof, of a refractory, inorganic oxide selected from magnesia, calcium oxide, zirconia, titania, boria, hafnia and a crystalline zeolite. A process for hydrotreating hydrocarbon oils containing sulfur compounds and/or nitrogen compounds comprising contacting said oil with hydrogen under hydrotreating conditions in the presence of a hydrotreating catalyst made by a method in acccordance with any one of claims 1 to 9.

Inventors: AKIZUKI, IKUO, KANEKO, YOSHIHITO, KAYA, HIROSHI, KUMAGAI, KEIJI, OKANO, SHOHEI, OTAKE, NOBUO, SAKURADA, SATOSHI, TAGAYA, NOBUAKI
Applicants: TOA NENRYO KOGYO KABUSHIKI KAISHA
Application year: 1985
Main classification: B01J35
IPC codes: B01J37, B01J35, C10G45, B01J23, B01J21, C01G45