Catalytic conversion of oxygen containing cyclic compounds. Part II. Cyclohexanone conversion on HZSM-5 zeolites

Abstract

Low-pressure on-stream conversion of cyclohexanone (CHN) was studied over HZSM-5 zeolites with various Si/ Al ratios (different number of strong acid sites). Each conversion run was followed by thermal decomposition of surface species which also were investigated using FTIR spectroscopy. It was found that, below 300°C, surface complexes consisting predominantly of CHN were held in the zeolites. The release of products, consisting of dehydrated CHN (C₆H₈), substituted aromatics and olefins, began above 250°C. The latter two compounds were formed via intermediates most probably of the aldol type (however, the dimerized methylcyclopentadiene intermediate cannot be excluded). The CHN dehydration to C₆H₈ predominated at 480°C. The yield of all products increased with the increasing number of zeolite strong acid sites. Ammonia, co-fed or preadsorbed, reacted with CHN to surface imines which hindered all other CHN reactions. The imine was strongly held in zeolites and decomposed at about 450°C to gaseous C₆H₈ and ammonia. Methanol partially methylated the reaction products but did not affect the main reaction routes, monomolecular dehydration and secondary intermolecular reactions.