Cyclization of cyclohexanone, formamide and ammonia in vapor phase gives l,2,3,4,5,6,7,8-octahydro acridin 9-ylamine (AOHA) over zeolites HY, HZSM-5, H beta and mesoporous Al-MCM-41 molecular sieves. The screening of catalysts clearly shows that Al-MCM-41 is more suitable for the vapor phase synthesis of AOHA. Correlation of activity and selectivity of metal ion-modified Al-MCM-41 with the NH3-TPD profiles shows that though the conversions are high, the formation of AOHA is governed by the acid site strength formed by the metal ion used. Interestingly Co2+ ion modification of Al-MCM-41 resulted into two sets of acid sites with T-max around 218 degrees C (weak-medium) and 673 degrees C (strong). The typical acidity available on Co-Al-MCM-41 around 300-350 degrees C is showing 100% cyclization activity facilitating the maximum synthesis of AOHA. Based on the product distribution a plausible reaction mechanism is proposed. (c) 2007 Published by Elsevier B.V.