Catalytic conversion of oxygen containing cyclic compounds. Part I. Cyclohexanol conversion over H[Al]ZSM-5 and H[B]ZSM-5

Abstract

Cyclohexanol (CHL) conversion was measured under low-pressure on-stream conditions on HZSM-5 zeolites and on H-boralite using small amounts of catalysts. Catalytic runs were followed by TPD of the surface species, which also were studied using FTIR spectroscopy. It was found that the individual reaction steps, low-temperature dehydration (yielding cyclohexene), skeletal isomerization (ring contraction to methylcyclopentene) and reactions involving H-transfer (formation of methylcyclopentane, substituted aromatics and simple olefins) were conditioned by the presence of strong acid sites whose number needed for these reactions increased from the dehydration to the H-transfer reactions. The CHL reaction was compared with the reactions of cyclohexene, and the effect of Lewis acid sites present in some cases together with the Brønsted sites was discussed. Ammonia was found to block the active centers, reduce the isomerization and especially the reactions involving H-transfer. Contrary to ammonia, methanol reacted with the CHL surface complexes yielding more substituted aromatics and more olefins than CHL or methanol alone (and/or simple sum of CHL and methanol products).