TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The composition further comprises and a binder. The zeolite is partially in acidic form. The molar ratio of SiO2/Al2O3 in the zeolite is 3 - 400 (preferably 5 - 50). The catalytic compositions comprise Y-zeolite and La together with Zn and Mo, Y-zeolite and La together with Zn and Cu. The composition comprises (wt.%) Zn, Mo, Cu, Ga, In, W, Ta, Zr or Ti (0.1 - 50, preferably 0.5 - 30), group VIII (0.001 - 10, preferably 0.1 - 5), lanthanide (0.5 - 20, preferably 1 - 15)Preferred Components: The Me is selected from Pt, Pd, Ti, Zn, Mo, Cu, Ni, Zn/MO, Cu/Zn, Pd/Ti and Ni/Mo and is present in the form of an oxide, ion and/or metal. The lanthanide is lanthanum and is present in the form of an oxide, ion and/or metal. The binder is silica, alumina or clay.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The composition further comprises and a binder. The zeolite is partially in acidic form. The molar ratio of SiO2/Al2O3 in the zeolite is 3 - 400 (preferably 5 - 50). The catalytic compositions comprise Y-zeolite and La together with Zn and Mo, Y-zeolite and La together with Zn and Cu. The composition comprises (wt.%) Zn, Mo, Cu, Ga, In, W, Ta, Zr or Ti (0.1 - 50, preferably 0.5 - 30), group VIII (0.001 - 10, preferably 0.1 - 5), lanthanide (0.5 - 20, preferably 1 - 15)Preferred Components: The Me is selected from Pt, Pd, Ti, Zn, Mo, Cu, Ni, Zn/MO, Cu/Zn, Pd/Ti and Ni/Mo and is present in the form of an oxide, ion and/or metal. The lanthanide is lanthanum and is present in the form of an oxide, ion and/or metal. The binder is silica, alumina or clay.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: (P1) is carried out in the presence of hydrogen at a pressure of 5 - 200 (preferably 25 - 100) bar, at 200 - 700 (preferably 300 - 600)degreesC. The weight ratio of H2/charge is 0.1 - 1.4 (preferably 0.1 - 0.7). A paraffin is used as diluent in (P1). (P2) Involves treating the zeolite with lanthanide compound, treating the product obtained with Me, drying and calcining. The lanthanide is inserted in the zeolite in acidic form by ion exchange, optionally calcining the product, depositing Me by ion exchange, and drying and calcining the product.Preferred Components: The mixture comprises at least one hydrocarbon containing at least 6 carbon atoms, selected from aromatic compounds, open-chain alkanes or alkanes with cyclic structures, alkenes having at least one unsaturation with open chains or alkenes with cyclic structures having at least one unsaturations. The mixtures containing alkanes and/or alkenes are mineral oil fractions, or derive from the hydrogenation of mineral oil fractions, or from the hydrogenation of fractions from conversion plants. The mixtures containing aromatic compounds are fractions coming from thermal or catalytic conversion plants, or mineral oil fractions. The fractions are pyrolysis gasolines, fractions coming from pyrolysis gasolines or residual fractions coming from production plants of aromatic compounds and reforming. The aromatic compounds are toluene, ethyl benzene, xylenes, benzene, C9 aromatic compounds and/or derivatives of naphthalene. The fractions are mixed with heavy fractions coming from fuel oil from steam cracking (FOK) or Light Cycle Oil (LCO) from fluid bed catalytic cracking. The mixtures are heavy fractions coming from fuel oil from steam cracking (FOK) or LCO from fluid bed catalytic cracking, previously treated to remove the asphaltenes. The resulting fraction of n-alkanes prevalently comprise ethane, propane, n-butane and n-pentane. The product comprises the fraction of n-alkanes containing 2 - 5 carbon atoms (50 - 90 wt.%). EXAMPLE - Y-zeolite (30 g) was impregnated with one third of a solution of ammonium heptamolybdate (2.316 g) and demineralized water (62.4 g) using the incipient wetness imbibition technique, dried at 120degreesC, impregnated again with a third of the solution, dried again, further impregnated with the remaining volume of the solution, dried and then calcined at 500degreesC for 4 hours. A catalyst was obtained with Mo (4 wt.%). The material was crushed to granules (20 - 40 mesh).