A catalyst composition and a process of using a catalyst composition for preparing high molecular weight hydrocarbons, such as polymethylene, from a fluid containing hydrogen and carbon monoxide are disclosed. The catalyst composition contains ruthenium and zirconium. The zirconium can be present as a zirconium component that can be selected from zirconyl phosphate, zirconium oxide, and zirconium phosphate prepared by processes of the present invention.