Phosphatation of Zeolite H-ZSM-5: A Combined Microscopy and Spectroscopy Study

A variety of phosphated zeolite H-ZSM-5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse Al-27, Si-29, P-31, H-1-P-31 cross polarization (CP), Al-27-P-31 CP, and Al-27 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X-ray microscopy (STXM) and N-2 physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H-ZSM-5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue. Phosphatation of pre-steamed H-ZSM-5 gives rise to the formation of a crystalline tridymite AlPO4 phase, which is found in the mesopores of dealuminated H-ZSM-5. Framework aluminum species interacting with phosphorus are not affected by hydrothermal treatment. Dealuminated H-ZSM-5, containing AlPO4, retains relatively more framework Al atoms and acid sites during hydrothermal treatment than directly phosphated H-ZSM-5.