Teresa Álvaro-Muñoz

Microwave-assisted synthesis of plate-like SAPO-34 nanocrystals with increased catalyst lifetime in the methanol-to-olefin reaction

Nanocrystalline SAPO-34 catalysts were obtained using microwave-assisted hydrothermal synthesis. Compared to conventional heating, the use of microwave irradiation shortened the crystallization time from days to several hours, resulted in a lower level of silicon incorporation, which led to slightly lower acidity, and modified the crystal size and morphology. The SAPO-34 catalyst synthesized in a microwave oven exhibited a longer lifetime in the methanol-to-olefin reaction due to its thin plate-like crystal morphology, which facilitates accessibility of the reactant to the acid sites.

Mesopore-Modified SAPO-18 with Potential Use as Catalyst for the MTO Reaction

SAPO-34 silicoaluminophosphates are well known as catalysts for the synthesis of light olefins–ethylene and propylene–from methanol by using the methanol to olefins (MTO) process, first described by Mobil. SAPO-18, which has a microporous framework structure related to but crystallographically distinct from SAPO-34, has been much less studied but promises to be a potential catalyst in the MTO process. The main drawback of these catalysts in this reaction is their rapid deactivation, due to the deposition of heavy carbonaceous products–coke–on the surface of the solid avoiding the access of methanol molecules to the active centres located inside the pores of the SAPO catalysts. We have used different mesoporogen agents–nanoparticulate carbons and chitosan–aiming to generate mesoporosity in the SAPO-18 crystals, in an attempt to improve the accessibility of the reagent to the active centres of SAPO-18 and, in that way, inhibit catalyst deactivation. All the materials prepared in this work present similar framework composition and silicon distribution and the main difference among them is the hierarchical porosity generated by the mesoporogen additives use in the synthesis, as determined by STEM. Using chitosan polymer as a secondary template results in an increase of the external surface, which improved significantly the internal diffusivity enhancing the life time of the catalyst in the MTO process.