Correlating NH3-TPD and 1H MAS NMR measurements of zeolite acidity:: proposal of an acidity scale

The acidities (number and strength of the Bronsted acidic sites) of two zeolite samples, H-MFI and H-BEA, were measured by ammonia temperature-programmed desorption (ATPD) and proton nuclear magnetic resonance (H-1 MAS NMR). Deconvolutions of the ATPD and H-1 MAS NMR spectra lead to acid sites distributions (number and strength) that are nearly similar. Acid sites of increasing acid strength are characterized by higher desorption temperatures and higher H-1 NMR chemical shifts. A linear relationship was found between the activation energy for ammonia desorption and the H-1 NMR chemical shift. The acid strength distributions determined by ATPD and H-1 MAS NMR have been quantitatively correlated. (c) 2005 Elsevier B.V. All rights reserved.