Title: Study of Zeolite Acid Properties by Solid-State NMR 

Detailed Description:

Zeolites have unique properties, such as porosity, acidity and thermal stability, of interest for a wide range of academic research and industrial applications. In this PhD project, several ZSM-5 zeolites (Zeolite Socony Mobil–5) with distinct Brønsted and Lewis acid properties at the internal and external pore surfaces will  be prepared and investigated through multinuclear 1D and 2D solid-state NMR (SSNMR) and dynamic nuclear polarization (DNP) surface-enhanced SSNMR. Phosphorous containing probes show a great potential to achieve a complete characterization of zeolite acid properties by 31P SSNMR. Past results from CICECO-Aveiro Institute of Materials revealed that the interaction of TMPO with Brønsted and Lewis acid sites is a powerful source of structural information on the pore surface. There is considerable controversy regarding the correct interpretation of the Brønsted and Lewis acid regions detected by 1D 31P SSNMR in TMPO-loaded zeolites. Zeolites enriched in 29Si and 17O isotopes will be used to comprehensively characterize the pore surface by multidimensional SSNMR. We anticipate using 1D and 2D homonuclear and heteronuclear correlation techniques, such as high-resolution 1H SSNMR, 1H-X HETCOR MAS NMR (X=29Si, 31P, 17O), DQ-SQ correlation spectroscopy and double/triple resonance recoupling methods (e.g., RESPDOR, REAPDOR, TRAPDOR) using conventional and DNP surface-enhanced SSNMR methods. The SSNMR study of a group of ZSM-5 zeolites with adjusted acid properties will settle controversial assignments reported in the literature. Cluster-based computational DFT methods will be used to investigate the interaction between TMPO and the Brønsted acid sites of a 8T HZSM-5 model using GAUSSIAN and VASP software packages.