13-P-23-Characterization of acidic sites in zeolites by heteronuclear double resonance solid state NMR

Abstract

This chapter presents the characterization of acidic sites in zeolites by heteronuclear double resonance solid-state nuclear magnetic resonance (NMR). The structural characterization of Brönsted acid sites in zeolites can be investigated through heteronuclear double resonance NMR experiments under magic angle spinning (MAS). With these experiments, the 1 H- 27 Al heteronuclear dipolar interactions are recoupled by using the rotational echo adiabatic passage double resonance (REAPDOR) technique. The signal evolution is followed and monitored under MAS, and the REAPDOR fraction is experimentally measured. Its time evolution is shown to reflect the differences in Brönsted acidity of three well-known zeolites—namely, LTL, LTY, and MOR.