The invention relates to a process for converting hydrocarbons with a catalyst comprising a crystalline molecular sieve composition which is obtainable by crystallizing a pre-formed extrudate mixture in a reactor and, during crystallization, removing excess alkali metal hydroxide from the pre-formed extrudate. The pre-formed extrudate mixture comprises at least one source of ions of tetravalent element Y, at least one source of alkali metal hydroxide, water, optionally at least one seed crystal, and optionally at least one source of ions of trivalent element X. The reaction mixture has the following mole composition: Y:X2=10 to infinity; OH−:Y=0.001 to 2; and M+:Y=0.001 to 2; wherein M is an alkali metal. The amount of water in the mixture is at least sufficient to permit extrusion of said reaction mixture.