TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation (Claimed): Preparation of the catalyst involves: a precipitation phase in a basic aqueous solution of a zirconium alcoholate which precipitates in the form of finely subdivided ZrO2, a precipitation phase of the iron oxide and promoter oxides (A) for feeding the corresponding hydrolysable salts, an addition phase of at least one precursor P-B of the promoter(s) (B), where the precursor of the promoter (B) is selected from metal arenes of formulae (I), (II), (III), and/or (IV), an addition phase of a hydrolysable salt of ruthenium, and hydrothermal treatment of the suspension resulting from the previous phases. The preparation process involves adding a zirconium alcoholate in an alcohol solution, preferably a solution of the alcohol of the corresponding alcoholate, to a basic aqueous solution, preferably a solution of KOH, obtaining a precipitate of ZrO2; adding at least one hydrolysable iron salt and a hydrolysable salt of a metal selected from metals of group IB, IIB and IIIA; separating the precipitate and drying it; re-suspending the solid resulting from the drying in a solvent selected from benzene, toluene and xylenes and adding at least one precursor P-B of promoters (B) selected from metal-arenes of formulae (I), (II), (III) or (IV) in a solution of the same solvent, to the resulting suspension; separating the solid resulting from the previous step, re-dispersing it in an aqueous solution of a base, preferably KOH, and adding a hydrolysable salt of Ru; separating the solid obtained in the previous step, re-dispersing it in water and maintaining it in an autoclave under hydrothermal conditions; separating the solid obtained in above step. The hydrothermal treatment is carried out at a temperature of 120 to 180 degrees C and a hydrogen pressure of 3 to 6 MPa. Preferred Components: The iron oxide is in a quantity of 1 wt.% to 20 wt.%, with respect to the weight of the catalyst. The promoter (A) is selected from gallium oxide (Ga2O3), zinc oxide (ZnO), and/or copper oxide (CuO). The promoter (A) is in a quantity of 1 to 20 wt.%, with respect to the metallic ruthenium. Preferred Catalyst: The catalyst contains ruthenium in a quantity of 20 wt.% to 55 wt.%, with respect to the weight of the final catalyst, expressed as metal element. The Ti, Zr, Hf and V are present in the final catalyst in a quantity of 0.2 to 5 wt.%, expressed as weight of the metal, with respect to the weight of the catalyst.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The hydrogenation process involves charging the catalyst into an aqueous solution containing an alkaline hydroxide; charging the aromatic or polyunsaturated compound into the aqueous solution, under stirring; reacting the aromatic or polyunsaturated compound with a continuous flow of hydrogen; at the end of the reaction, recovering the selectively hydrogenated compound by de-mixing the organic phase from the aqueous phase and distillation of the organic phase. The hydrogenation process is carried out at a temperature of 120 to 180 degrees C and a pressure of 4 to 6 MPa. Preferred Definitions:    arenes=benzene, toluene, ortho-xylene, meta-xylene, para-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and/or hexamethylbenzene.    EXAMPLE - Synthesis of Ti( eta 6-benzene) (AlCl4)2 (P-B-1) was carried out as follows: 6.72 g of sublimated AlCl3 and TiCl4 (4.55 g) were added to a suspension of aluminum in powder form (3.95 g) in benzene (150 ml). The mixture was left at reflux temperature (120 degrees C) for 20 hours. It was then filtered on a porous septum and the solution obtained was subsequently reduced to about 30 ml by evaporation of the solvent under vacuum. 150 ml of n-heptane were added to the residue and the mixture obtained was then placed in a refrigerator at about 4 degrees C, for 24 hours. The purplish solid precipitated was recovered by rapid filtration of the suspension, washed with heptane and dried under vacuum. The solid formed had metal content (wt.%): Ti of 10.3%, Al of 12.5%, whereas the content of Cl, determined by means of potentiometric titration, was 62.8%. Synthesis of Zr( eta 6-benzene)2 (Al3Cl11) (P-B-2) was carried out as follows: a suspension of aluminum in powder form (5.06 g) in benzene (430 ml) was treated with fresh sublimated AlCl3 (8.60 g) and ZrCl4 (7.16 g). The mixture was left at reflux temperature (120 degrees C) for 24 hours. The suspension was then filtered under heat on a G3 filter, and the solution obtained was subsequently reduced to about 100 ml by evaporation of the solvent under vacuum. 150 ml of anhydrous n-heptane were added to the residue and the mixture was left under vigorous stirring for about 1 hour and then placed in a refrigerator at about 4 degrees C, for 24 hours. The dark solid precipitated was recovered by rapid filtration of the cold suspension, washed with benzene and dried under vacuum, obtaining 10.5 g. The solid had following metal content (wt.%): Zr of 11.7%, Al of 12.8%, whereas the content of Cl, determined by means of potentiometric titration, was 55%. Preparation of the catalyst was carried out as follows: 40 ml of a solution of KOH at 10% was introduced into a 250 ml flask and 1 ml of Zr(OPr)4 at 70% in i-PrOH was then rapidly added under stirring. The formation of ZrO2 was practically immediate. It was left to digest under stirring for 15 minutes. The following products were rapidly added to the suspension, in sequence: 10 ml of a solution of FeCl3.7H2O at 4 wt.%, left to homogenize for 15 minutes, then 10 ml of H2O with 60 mg of Ga2(SO4)3.H2O dispersed in it, and finally 10 ml of a solution of ZnSO4.H2O at 0.6 wt.%. The suspension was left under vigorous stirring for a further 15 minutes, subsequently centrifuged at 2000 revs for 10 minutes and the precipitate recovered and dried. The solid was transferred to a dry box in an anhydrous and oxygen-free atmosphere, and then re-dispersed in anhydrous benzene under stirring. 10 ml of a solution of the precursor P-B-1 prepared in above and the precursor P-B-2 in benzene (100 mg+100 mg in 10 ml) were added to the dispersion thus obtained and the suspension was left under stirring for 20 hours at room temperature. The suspension was extracted from the dry box and water was added, the solid was finally centrifuged at 2000 revs for 10 minutes. The solid was washed with ether, centrifuged again and dried in an oven at 100 degrees C. The solid was subsequently dispersed in an aqueous solution of KOH at 10% and a solution of RuCl3 (10 ml at 3.2% as Ru) was added to this. The suspension was then brought to a temperature of 80 degrees C, always under stirring, in 60 minutes, by means of a thermostat-regulated oil bath, and left at this temperature for 1 hour. The stirring and heating were interrupted and the solid is left to cool and settle for 18 hours. After this period, the supernatant liquid was eliminated after centrifugation at 2000 revs for 10 minutes. The solid was dispersed in 40 ml of H2O and transferred to a 250 ml autoclave coated with PTFE. The reactor was pressurized with 40 atm of H2 and brought to a temperature of 150 degrees C in an hour under stirring (5000 revs per minute), obtaining a final pressure of 50 atm. The system was left under these temperature and pressure conditions under mechanical stirring for 1 hour, then left to cool slowly and settle for 18 hours. The autoclave was depressurized and the suspension of the catalyst was transferred to a glass to which 40 ml of H2O were added. The whole mixture was left under stirring in air for 5 hours in order to obtain passivate particles of Ru and avoid oxidation phenomena. The solid was finally separated from the liquid by centrifugation at 2000 revs for 10 minutes and dried under vacuum with a rotating pump at 3 torr for 20 hours. About 0.9 g of catalyst with 40% of Ru was obtained from this preparation, which was preserved in a drier. The catalyst was then used in selective hydrogenation of benzene. The initial selectivity was found to be 86% and yield was 55%.