Effects of F/Nb mol ratio of F-Nb/HZSM-5 catalyst on the catalytic performance for ethanol dehydration to ethylene

The structures and surface acidities of F-Nb/HZSM-5 catalysts with different F/Nb mol ratio were studied using BET, NH₃-TPD, FT-IR, MAS-NMR and SEM. The catalytic performance of these catalysts for ethanol dehydration to ethylene was evaluated and correlated with the characterization results. It is found that, dealumination of HZSM-5 occurred after modification and the depth of dealumination increased with the increase of the amount of F added. The extra-framework aluminum species were observed by ²7Al MAS NMR with a signal appeared at -13.5. With the increase of F/Nb mol ratio, both weak and strong acid amounts decreased and a new strong acid site was found in the NH₃-TPD profile at 500℃. The catalyst with F/Nb mol ratio of 0.7 gave the highest catalytic activity and selectivity. The stability of the catalyst was greatly improved by the addition of F-Nb.