Investigation of Microstructure of Zeolite Type Material by <sup>1</sup>H NMR Spectroscopy and Thermogravimetric Analysis

Abstract

The application of temperature programmed desorption (TPD) of ammonia as a probe base molecule from synthetic ultrastable faujasite type zeolite is presented. In order to determine the positions and strength of active acid sites in a microstructure of zeolite materials, desorption was monitored by pulse 1 H NMR spectroscopy and thermogravimetric analysis. In performed experiment, the temperature dependence of spin-lattice relaxation time T 1 (namely of two components resolved by spin-grouping technique) was scanned as well as of corresponding relative change in sample mass. The results obtained in this way show considerably higher values of T 1 in certain temperature ranges. and higher values of mass loss in the very same intervals. These results confirm the existence of low temperature peaks (LTP) when slightly bound protons of ammonia leave the samples. These peaks are related to weak and medium active sites, i.e. to silanol groups (SiOH) on external surface of crystal lattice and hydroxyl groups within large, α, super-cages, respectively. High temperature peaks (HTP) were also observed. They originate from La 3+ ions located inside small, β, sodalite cages, acting as strong active centres, from which the tightly bound protons of ammonia are released during desorption.