Synthesis and Characterization of Microporous Aluminophosphates of AFI Topology

摘要

Aluminophosphates of the AFI (aluminophosphate-5) topology were synthesized and characterized in order to study the influence of acid strength and distribution for the possibility of both conversion and selectivity for oligomerization reactions. It is well known that weaker acid sites lead to a product shift to hydrocarbons of lower carbon chain length and a lower conversion, and a reduction in acid site concentration has a similar effect. However, when a silylating agent modifies the surface acidity, the overall conversion drops, associated with a reduction in sticking probability of an olefin on the silicoaluminophosphate's (SAPO) crystal surface. This is associated with a reduced ability of the surface acid sites to crack the products upon exiting the internal pore system. This research reports on the synthesis and charactizeration of microporous aluminophates of AFI topology. Catalysts' properties were characterized by a series of spectroscopic and diffraction techniques, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). All catalysts were characterized in calcined form.