Abstract: In order to determine qualitatively and quantitatively the internal and external acid sites of ZSM-35 zeolites, three types of ZSM-35 samples (GNJ, GNX, and GW) prepared under different crystallization and calcination conditions were characterized using NH3-TPD and 31P MAS NMR with different probe molecules. The selectivity and activity of n-butene isomerization of different catalysts were investigated. The results showed that the amount of Bronsted acid site in ZSM-35 zeolites were much more than Lewis acid site, the acid strength and amount on ZSM-5 zeolite were different according to preparation conditions. GNJ had a kind of weak Bronsted acid site, GW had three kinds of Bronsted acid sites with different strengths, the weaker Bronsted acid sites were distributed inside and outside the channel and the stronger two kinds of Bronsted acid sites were mainly distributed inside the channel. GNX had two kinds of Bronsted acid sites of different strengths and distributed inside and outside the channel. Bronsted acid amount of GNX was more than the other two samples. It is recognized that the medium strong Bronsted acid was an essential for isobutene formation. Therefore, the ZSM-35 molecular sieve with appropriate suitable medium-strong Bronsted acid and distribution was beneficial to the n-butene isomerization reaction.

Key words: ZSM-35 zeolite, isomerization, acidity, solid-state nuclear magnetic resonance, probe molecule