TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Additive: The additive is a metal chloride or organic chloride compound. The concentration of additive in (1) is 0.05 - 200 parts by weight per billion. Preferred Compound: The feed stream comprises impurities selected from carbondioxide and carbon monoxide. The catalyst comprises platinum and inorganic support material (preferably zeolite). The concentration of platinum in the catalyst is from 0.01 - 10 wt.%.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Additive: The additive is a metal chloride or organic chloride compound. The concentration of organic chloride compound in (1) is from 0.01 - 700 (preferably 0.05 - 600) part by weight per million parts. Preferred Compounds: The alkane is n-butane, n-pentane, n-hexane, 2-methylpentane, 3-methylpentane, n-heptane, 2-methylhexane, 3-methylhexane, octanes, nonanes and/or decanes. The cycloalkane is (methyl)cyclopentane, (methyl)cyclohexane and/or (methyl)cyclooctane. At least one feed hydrocarbon is a mixture of normal hexane, methylcyclopentane and cyclohexane or n-butane. The feed stream comprises impurities selected from sulfur compounds, water, 6 - 10C aromatic hydrocarbons and/or 2 - 10C olefin hydrocarbons.Preferred Process: The isomerization is carried out at a temperature from 37.7degreesC - 316degreesC. The pressure is from below atmospheric pressure to 4823 kPa. The charge rate of at least one feed hydrocarbon is from 0 hour-1 to 1000 hour-1. The molar ratio of hydrogen to hydrocarbon of at least one feed hydrocarbon is from 0.01:1 - 20:1. The concentration of the additive in (1) is maintained by continuously or intermittently injecting the additive into (1). At least one product hydrocarbon isomer is recovered from the effluent exiting the isomerization zone. The molar ratio of normal hexane to methylcyclopentane in the mixture is from 1:99 - 99:1 (preferably 1:90 - 90:1). SPECIFIC COMPOUNDS - Aluminum chloride, antimony chloride, antimony pentachloride, tin(II) chloride, tin(IV) chloride, titanium(III) chloride, titanium(IV) chloride and/or zinc chloride are specifically claimed as metal chloride. Carbon tetrachloride, tetrachloroethylene, hexachloroethane, 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methyl propane, 2-chloro-2-methyl propane are specifically claimed as organic chloride.    EXAMPLE - A mixture containing perchloroethylene (PCE) and an additive comprising aluminum chloride (AlCl3) (1.8 ppb) was added to liquid alkane-containing feed to maintain the concentration of AlCl3 (1.8 ppb) and PCE (83 ppm) in the liquid alkane-containing feed. The catalyst was conditioned with a hydrogen-to-hydrocarbon (H2:HC) molar ratio of 2.7:1 for 24 hours using the mixture of AlCl3 and PCE. The isomerization of butane did not decrease but remained steady at various H2:HC molar ratios throughout the run. At a H2:HC molar ratio of about 0.20:1 the isobutene product ratio remained steady at an average of about 143 hours. This indicates that the activity of the isomerization catalyst was maintained. A control was prepared in the same way without using AlCl3. The butane continually decreased at various H2:HC molar ratios throughout the run. The isobutene product ratio also decreased. This means the run life of isomerization catalyst can be extended and the catalyst d eactivation problems can be alleviated or diminished by the use of AlCl3 additive at low concentration.