TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - The catalyst comprises at least an alkaline or an alkaline earth metal or at least a metalloid and at least a halogen or a halogeno compound. The charge comprises of paraffin, naphtene and aromatic hydrocarbons containing 5-12C atoms per molecule. The metal of group VIII is chosen from iridium, nickel, palladium, platinum, rhodium, and ruthenium or preferably platinum or palladium. M is chosen from germanium and tin. The precursor of element M is chosen from hydroxides, halogeno compounds, carbonates and carboxylates of organic compounds of element M, compounds of general formula (R1)xM(R2)y where x + y = valency of metal M and or R1 is chosen from alkyl, cycloalkyl, aryl, alkylaryl and arylalkyl and R2 is a function of CaHbR'c form, where R' is hydroxide, carboxylate, POH3 or SO3H functional group. M is preferably chosen from carboxylates of organic compounds of element M and is tributyl tin acetate. The additional element M, optionally halogen or halogeno compound, optionally an alkaline or alkaline-earth metal, optionally a metalloid is introduced successively or simultaneously onto the support using sol-gel technique. An organic solution of an alcoxy compound of the metal's support is hydrolyzed with an aqueous solution of an organometallic compound M. EXAMPLE - Two catalysts A and B each containing 0.7 wt.% Pt and 0.15 wt.% Sn were selected. The support was a silica from Degussa of specific area of 200 m2/g. For Catalyst A (comparative example): The support was calcined at 500 degrees C under dry air then contacted an ammonia solution (1N) under nitrogen bubbling. Pt was deposited by the introduction of tetramine Pt hydroxide solution. The suspension was then filtered, washed with distilled water and dried at 110 degrees C under nitrogen. 3 g of the solid containing 0.7 wt.% Pt was reduced under hydrogen during 4 hours at 450 degrees C. The catalyst was then loaded in a reactor containing heptane under hydrogen. Tetrabutyltin was then injected at 20 degrees C. After 24 hours of reaction at ambient temperature under hydrogen atmosphere, the solid was filtered, washed with heptane then dried at 80 degrees C. It was then reduced under hydrogen flow at 550 degrees C for 4 hours. Catalyst B (according to invention) was prepared from 3g of the solid at 0.7 wt.% Pt. It was reduced under hydrogen at 450 degrees C for 4 hours. The catalyst was then loaded in a reactor under hydrogen containing 500 cm3 of an aqueous ammonia solution (pH = 11) containing 4.5 mg Sn (Bu3SnOC(O)CH3) form. After 24 hours of contact under hydrogen atmosphere, the reaction mixture was filtered, washed, then dried at 80 degrees C. It was then reduced under hydrogen flow at 550 degrees C for 4 hours. The two catalysts were subjected to dehydrogenation test of isobutane which was carried out in a tubular isotherm reactor. 1 g of catalyst was reduced at 550 degrees C for 2 hours under hydrogen flow of 2 l/hr.. After injection of the feed, the temperature was stabilized at 550 degrees C. The analysis of the gaseous effluents was carried out on line by gas chromatography. The operating conditions were: a feed of iC4 Air liquid N35; 550 degrees C; 0.1 Mpa; H2/iC4(molar) 1; and weight flow of liquid per hour iC4/mass of catalyst : 725 h-1. The results were: for Catalyst A at 1, 3 and 5 hours, activities of 20.0, 18.4 and 17.6 and selectivities for iosbutene of 99.1, 99.1 and 99.3 respectively; and for Catalyst B at 1, 3 and 5 hours, activities of 25.0, 23.5 and 23.0 and selectivities for isobutene of 99.2, 99.2 and 99.3 respectively. The results showed that the catalyst B prepared according to the invention gave identical or improved performances than catalyst A.