This invention relates to a catalyst for the conversion of synthesis gas or methanol to hydrocarbons and to a process for its production. The catalyst comprises a highly porous amorphous silica having a monolayer of an amphoteric metal chemically bonded onto up to 90% of the surface area of the silica matrix. The catalyst has a maximum pore diameter of 1.5 nm and the metal is preferably aluminium. The catalyst is produced by treating the silica with a solution of a hydrolysable aluminium compound, removing the solvent and causing the silica surface to hydrolyse the compound, thus chemically bonding the aluminium onto the surface of the silica matrix. Optionally, the catalyst is mixed intimately with a Fischer-Tropsch catalyst to enable the direct conversion of synthesis gas to hydrocarbons. The catalyst will be of use in the conversion of synthesis gas or methanol to higher hydrocarbons.