Influence of different processes of dealumination on acid properties of an H-ferrierite zeolite

Abstract

Samples of H-ferrierite (H-FER) zeolite with different Si/Al ratios were obtained through several dealumination methods: calcination, steam treatment, acid leaching after steam treatment and ionic exchange with ammonium and silicon hexafluoride. The X-ray diffraction and BET results showed that aluminum extraction from the framework did not affect the ferrierite crystallinity and textural properties. Measurements of 29Si and of 27Al MAS Nuclear Magnetic Resonance (NMR), infrared spectroscopy and ammonium TPD were used to characterize the acidity in these samples, and a good agreement was found between them. The NMR results showed that the dealumination occurred after the different treatments. The steam treatment dealuminated H-FER presented the higher dealumination degree. The aluminum removed from the zeolite framework by dealumination remained on the zeolite matrix even after acid leaching. The ammonium TPD profiles indicated that the steam treatment caused the higher zeolite H-ferrierite dealumination, since it caused a decrease of about three times on zeolite acidity. On the other hand, the sample treated with ammonium and silicon hexafluoride had a non-significant decrease in its acidity when compared to H-ferrierite. The catalytic tests for 1-butene isomerization showed that the sample acid leached after steam dealumination, with 60% of acid site concentration in relation to H-FER, presented the best selectivity to isobutene. It was concluded that it is not necessary to have a higher Bronsted acidity to obtain a high selectivity to isobutene during linear butenes isomerization.