ИСТИНА

Oligomerization of butene-butane feedstock into gasoline-range fuels has been studied over H-MFI zeolites with similar acid site density (Si/Al ~ 30) and different ratio of Brønsted sites on the external surface of zeolite polysrystals and inside micropores. The ratio was varied by 1) changing the size of zeolite polycrystals and 2) selective poisoning of Brønsted sites on the external surface by tetraethylorthosilicate (TEOS) treatment. It has been demonstrated that the decrease of polycrystalline size from 3 to 0.2 μm (or the increase of external sites content) leads to the significant increase of activity, accompanied by the intensive coke formation and the shift of selectivity towards light hydrocarbons. The results point to significant intracrystalline diffusion limitations in large polycrystals and suggest that the activity of MFI catalysts in butene oligomerization is governed by the active sites located on the external surface and subsurface of polycrystals.