This invention relates to a catalyst for usin the direct conversion of synythesis gas to olefinic hydrocarbons in good yield. tt also relates to a process for producing the catalyst. The catalyst comprises a highly porous amorphous silica support on which is deposited one or more monolayers of silica. The catalyst is then impregnated with a transition metal. The monolayer of silica is formed by the hydrolysis of a compound such as ethyl orthosilicate while it adsorbed onto the support.