In situ MAS NMR and UV/VIS spectroscopic studies of hydrocarbon pool compounds and coke deposits formed in the methanol-to-olefin conversion on H-SAPO-34

In situ ¹³C MAS NMR and UV/Vis spectroscopy were applied to study hydrocarbon pool compounds and coke deposits formed during the methanol-to-olefin (MTO) conversion on H-SAPO-34 at 623 and 673 K. These experiments were performed using an MAS NMR rotor reactor and, for comparison, a standard fixed-bed reactor. The ¹³C MAS NMR spectra recorded under steady-state conditions consist of characteristic signals of alkyl groups (18 to 29 ppm) and carbon atoms in aromatic compounds (125 to 135 ppm). The simultaneously recorded UV/Vis spectra consist of bands of dienylic (345 nm) and trienylic carbenium ions (430 nm), dienes (245 nm), polyalkylaromatics (280 nm), and polycyclic aromatics with chain-like topology, such as polymethylanthracenes (400 nm). ¹³C MAS NMR studies of the ¹³C/¹²C scrambling between ¹³C-enriched methanol and non-enriched organic deposits on used H-SAPO-34 catalysts support the paring mechanism for the growth of alkyl groups at polyalkylaromatics during the methanol to olefin reaction.