Enhancement in catalytic performance of HZSM-5 zeolite for glycerol dehydration after acidity regulation

HZSM-5 zeolites modified by simple and economical impregnation with phosphoric acid were applied to acrolein production from glycerol. After 68 h on stream, the glycerol conversion was still maintained at 100 % with an acrolein selectivity of 89.6 % on phosphorus modified nanosheet HZSM-5, which ranks among the best catalytic performance in glycerol dehydration catalyzed by zeolites. Besides, improvement in catalytic stability was further confirmed by the lowered deactivation rate on phosphorus modified HZSM-5 zeolite. Characterization results revealed that the acidity of HZSM-5 zeolite was adjusted by phosphorus incorporation. More importantly, the regulative mechanism was thoroughly discussed basing on a comprehensive consideration of the 27Al MAS NMR and Py-IR results. Further investigation with in situ FT-IR indicated that products or intermediates in glycerol dehydration could be more easily desorbed from phosphorus modified HZSM-5 zeolite with weaker acidity, which dramatically suppressed coke formation and greatly prolonged the lifetime of catalyst. Moreover, for the first time, diffusivity calculation and experimental results illustrated that product diffusion restriction played a crucial role in producing acrolein with ultrahigh selectivity over HZSM-5 apart from acidity.