Verifying the dominant catalytic cycle of the methanol-to-hydrocarbon conversion over SAPO-41

In the present work, the mechanism of the methanol-to-hydrocarbon (MTH) conversion over the silicoaluminophosphate SAPO-41 with one-dimensional 10-ring pores has been investigated. For this purpose, catalytic experiments with co-feeding of reactants, in situFTIR and UV/Vis spectroscopy, and 1H MAS NMR spectroscopy of used catalysts upon loading of ammonia were performed. Using these methods, only a low content of aromatics could be observed on the working SAPO-41 catalyst. These findings and the characteristic changes in the ethene selectivity during the co-feeding experiments indicate that alkylaromatics can be excluded as active hydrocarbon pool compounds on SAPO-41 applied as MTH catalysts. On the other hand, dienes and enylic carbenium ions were detected using FTIR and UV/Vis spectroscopy and the formation of amines by reaction of alkenes with ammonia was detected via1H MAS NMR spectroscopy. These results are experimental evidence that large olefins partially existing in their carbenium state dominate the catalytically active hydrocarbon pool on the working SAPO-41. Due to this dominant alkene-based reaction mechanism and the limited formation of aromatics, SAPO-41 is a suitable catalyst for the C3+C4olefin as well as gasoline production.