H-Y and H-ZSM-5 zeolites were investigated by H-1 MAS NMR spectroscopy over a wide range of temperatures (160-773 K). Signal broadening by up to a factor of 5 and signal narrowing by up to a factor of 40 could be assigned to different hydrogen-ex change reactions in the zeolites. We found that hydrogen forms of a zeolite containing ammonium ions represent ammonium-conducting materials, but in zeolites that were activated at temperatures above 673 K, the hopping of the hydrogen atoms between different aluminum sites ( SiOHAl ) is independent of proton vehicles. (c) 2008 Elsevier Inc. All rights reserved.