The dynamics of retained and deactivating species in a SAPO-18 catalyst during the methanol-to-olefins reaction have been followed using a combination of ex-situ and in-situ techniques; performed in differential and integral reactors. The retained species have been analyzed using extraction, in-situ FTIR and in-situ UV-vis spectroscopies combined with online product analysis (gas chromatography and mass spectrometry). In particular, here we provide the detailed composition of the retained species given by the high-resolution mass spectrometry (LDI FT-ICR MS). We observe a decrease of both formation and degradation rates of retained species by water, whereas the extent of these decreases is the same across the entire spectrum of retained molecules. This result is profound because it indicates that added water unselectively quenches the formation of active and deactivating species. At the same time, the catalyst can have an extended lifetime by adding water and we proved that this is due to the expulsion of species (particularly olefins) out of the SAPO-18 framework, and subsequent growth of heavy polycyclic aromatic structures that imply less deactivation. These conclusions can be extrapolated to other MTO catalysts with relatively similar pore topology such as SAPO-34 or SSZ-13 structures.
ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry
- Organic Chemistry