TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - The catalyst support is in the form of extrudates or balls of 0.8 - 2 mm diameter. The surface area and porous vol. of the gamma alumina (if present) is 150 - 300 m2/g and 0.4 - 0.8 cm3/g, respectively, and for eta alumina (if present), 400 - 600 m2/g and 0.3 - 0.4 cm3/g, respectively.The group VIII metal is Pt, Pd or Ni.The preferred vapor treatment of the support is carried out in air or N2 containing 0.2 - 100 % vol. of water vapor at 200 - 700 degreesC for 0.5 - 0.6 hrs.The preferred halogen (chlorine) content is 4 - 15 %, and chlorination is effected by carbon tetrachloride or chloroform. EXAMPLE - A catalyst (A) was prepared from gamma alumina, formed by extrusion across a die of diameter 1.2 mm. The solid was then treated at 500 degreesC in air containing 3 % vol. of water vapor. 0.2 % of Pt was introduced by ion exchange with hexachloroplatinic acid in the presence of HCl, and the solid obtained reduced under H2 at 400 degreesC. Chlorination was then carried out at 280 degreesC by injection of CCl4 in a current of N2.    A comparative catalyst (C) was also prepared using a similar support. After a pre-calcination process in air, 0.2 % of Pt was introduced in a similar manner and the solid treated t 500 degreesC in dry air (containing less than 0.01 % vol. of water vapor). The product obtained was reduced under H2 at 400 degreesC. Chlorination was then effected in the same conditions as above.    The catalysts were tested on the isomerization of a charge comprising 50 % of C 5 n-paraffins, 40 % of C 6 n-paraffins and 8 % of C 6 n-naphthenes. The charge contained 100 ppm of CCl4.    The process was operated at 150 degreesC; 3 MPa; 1.3 h-1 p.p.h; and H2 / HC (in effluent) 0.47.    The results after 24 hrs, comparative for catalysts (A) and (C), were:    (1) 5 i-C / 5 (i+n)-C : 0.75, 0.70;    (2) 6 i-C / 6 (i+n)-C : 0.88, 0.85;    (3) AEQ i5 (%) : 91, 76;    (4) AEQ 2,2DMC4 (%) : 80, 59;    (5) 5 - 6 C cracking (%) : 1.8, 1.4.    AEQ ix (approach to equilibrium) = (i-Cx/ (i+n)-Cx in effluent) / (i-Cx/ (i+n)-Cx at equilibrium).    ix = isoparaffin with x C atoms where x = 4 - 8.