TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The silica-alumina of (1a) type has SiO2/Al2O-3 molar ratio is 50-300. The P/Al ratio of the porous solid material of (2) type is 0.3-3.5, preferably 0.5-2.5. The Si/Al atomic ratio of the porous solid material of (2) type is 20-200, preferably 25-150. The silica-alumina is an extruded material containing binders. A phosphorus-containing compound is added in step (C). The porous solid material of (2) type is bound with inert components. The catalytic composition contains metal(s) of group VIII from platinum, palladium, nickel, or cobalt as metal component (B). The catalytic system contains metal(s) of group VIII or metal(s) of group VIB and the metals of group VIII are nickel and cobalt. The catalytic system contains as metal component (b) metal(s) of group VIII and metal(s) of group VIB, and the metal of group VIB is molybdenum or tungsten. In the catalytic composition, the metal of group VIII is present at 0.1-5 wt.%, and the metal of group VIB is present at 1-50, preferably 5-35 wt.%. The catalytic component comprises metal(s) of group VIII and a silica alumina gel support, which is amorphous to X-rays, with SiO2/Al2O3 molar ratio of 30-500, a surface area of 500-1000 m2/g, a pore volume of 0.3-0.6 ml/g and an average pore diameter of 10-30 Angstrom . The catalytic composition contains metal(s) of group VIII and a calcined silica alumina gel support, which is amorphous to X-rays, with a SiO2/Al2O3 molar ratio of 30-500, a surface area of 500-1000 m2/g, a pore volume up to 0.8 ml/g and an average pore diameter of 10-40 Angstrom . The catalytic composition contains metal(s) from platinum, palladium, iridium, ruthenium, rhodium, or rhenium and a silica-alumina support, which is amorphous to X-rays, with SiO2/Al2O3 molar ratio of 30-500, a surface area greater than 500 m2/g, a pore volume of 0.3-1.3 ml/g and an average pore diameter smaller than 40 Angstrom . The catalytic composition contains a mixture of metals from groups VIB and VIII and a silica alumina gel support, which is amorphous to X-rays, with SiO2/Al2O3 molar ratio of 30-500, a surface area of 500-1000 m2/g, a pore volume of 0.3-0.6 ml/g and an average pore diameter of 10-40 Angstrom . The mixture is fed to the reactor in co-current with or in countercurrent to hydrogen. The hydrogen/mixture of biological origin ratio is preferably 400-2000 Nl/l. The catalytic composition is formed with platinum and a silica-alumina of the type (1) and the pretreatment is carried out at 100-500, preferably 200-400 degrees C and 5-50 bars. The catalytic composition is formed by a silica-alumina of (1) type, platinum and a binder and undergoes a pretreatment with a hydrocarbon containing 7-16C.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The mixture of biological origin is a mixture of vegetable or animal origin. The esters of fatty acids contained in the mixtures of biological origin are triglycerides of fatty acids, in which the hydrocarbon chain of the fatty acid contains 12-24C and is mono- or polyunsaturated. The mixtures of biological origin are vegetable oils, vegetable fats, animal fats, and/or fish oils. The oils and vegetable fats, deriving from selected plants through genetic manipulation, are sunflower, rape, canola, palm, soybean, hemp, olive, linseed, mustard, peanut, castor, coconut oils, fatty oils contained in the pine tree pulp, recycle oils and/or fats from food industry, and the animal oils or fats are bacon-fat, lard, tallow, milk fats, recycle oils and/or fats from food industry. The mixtures of biological origin are mixed with hydrocarbons before being fed to the method. Preferred Method: The porous solid material of (2) type in bound form is prepared by mixing the gel obtained through hydrolysis and gelification of the aqueous mixture of Al alkoxide, tetralkyl silicate, tetralkylammonium hydroxide and oxygenated phosphorus compound with an inorganic binder, an acidifying compound and a plastifying agent. EXAMPLE - A refined soybean oil was fed in a continuous reactor at 350 degrees C, liquid hourly space velocity (LHSV) of 0.5 hour-1 and 35 bar, and with hydrogen (H2)/oil ratio of 1500 Nl/l. The vegetable oil was fed with H2 in equicurrent in the presence of catalysts platinum (Pt)/extruded silica alumina (MSA) and Pt/extruded phosphorus (P)-MSA. The reactor was a reactor operating in continuous with a downward flow. When the Pt/extruded MSA catalyst was used, a pre-treatment was carried out including reduction with hydrogen at 35 atm, from 30-340 degrees C in 16 hours, 340 degrees C for 2 hours followed by treatment with a hydrocarbon containing 16C. The temperature was brought to 320 degrees C in the presence of hydrogen. The pre-treatment with the hydrocarbon was effected at LHSV of 1 hour whereas the H2/hydrocarbon ratio was 1500 Nl/l. The effluent product was separated, in a gas/liquid separator, from the gaseous fractions containing H2, carbon monoxide/carbon dioxide and 3C/4C light paraffins. After separation of the water, the liquid product proved to contain paraffins, with 5-22C. Analysis of the liquid phase by means of gas chromatography gave higher than 80% as isomerization degree. The hydrocarbon product was sent to a distillation column to separate the gasoline fraction (10%) from the diesel fraction (90%). The total aromatic compounds formed were 5.3% w/w in the case of the catalyst Pt/MSA, and 2.5% w/w in the case of the catalyst Pt/P-MSA.