The Effect of Acid Sites in Skeletal Isomerization of N-Butenes over Ferrierites and Coalpo-11

Abstract

Acid sites of H-, NaH-ferrierites and those partly or fully dehydroxylated, and CoAlPO-11 were characterized by TPD of ammonia, UV-VIS spectroscopy, IR spectroscopy of D3-acetonitrile and by transformation of n-butenes. It has been shown that the high density of strong bridging OH groups or their simultaneous presence with strong Lewis sites support oligomerization reactions to higher olefins, leading via cracking to C3-C5 olefins, C4 paraffins and some coking. Thus, a low density of strong OH groups and absence of Lewis sites led to the selective performance of ferrierite. Under the same reaction conditions CoAlPO-11 with very low number of acid sites exhibited the highest and moreover stable activity to isobutene (yield 45 % at 620 K) for at least 48 hrs. This is a result, besides very narrow channels, of cooperative effect of weakly acidic both P-OH groups and Co2+ Lewis sites. When P-OH groups were completely removed by calcination, skeletal isomerization selectively proceeds only on Co2+ sites.