Process for preparing a catalyst composition containing a modified crystalline aluminosilicate and a binder, wherein the catalyst composition comprises from 5 to 95% by weight of crystalline aluminosilicate as based on the total weight of the catalyst composition, the process being remarkable in that it comprises a step of steaming said crystalline aluminosilicate: at a temperature ranging from 100° C. to 380° C.; under a gas phase atmosphere containing from 5 wt % to 100 wt % of steam; at a pressure ranging from 2 to 200 bars; at a partial pressure of H2O ranging from 2 to 200 bars; and said steaming being performed during at least 30 min and up to 144 h; and in that the process also comprises a step of shaping, or of extruding, the crystalline aluminosilicate with a binder, wherein the binder is selected to comprise at least 85 wt % of silica as based on the total weight of the binder, and less than 1000 ppm by weight as based on the total weight of the binder of aluminium, gallium, boron, iron and/or chromium.