Investigations on the reaction mechanism of the skeletal isomerization of n-butenes to isobutene Part II.: Reaction mechanism on ferrierites

Ferrierites with Si/Al ratios between 20 and 70 were tested as catalysts for the skeletal isomerization of n-butenes to isobutene in the temperature range from 573 to 773 K. After 10 min time on stream (TOS) selectivities to isobutene between 50 and 92% were obtained, after 6h between 73 and 96%. depending on the Si/Al ratio of the samples, the conversion of n-butenes and the reaction temperature. A clear trend of increasing selectivity to isobutene with increasing Si/Al ratio, increasing temperature, and decreasing conversion of n-butenes was observed. Furthermore, the coke content of the samples after reaction was determined. It was to low for a pore blockage of the samples with Si/Al ratios >40. The results are discussed considering the different reaction mechanisms for the isomerization of n-butenes to isobutene proposed in the literature. The monomolecular mechanism is assumed to be the main reaction path for the formation of isobutene on ferrierites. TPAD experiments established that the selectivity to isobutene is influenced rather by the number of acid sites than by the acid strength. (C) 2001 Elsevier Science B.V. All rights reserved.