Nature of the acidic protons in H-mordenite and H-MCM-22 as studied by variable temperature 1H MAS NMR1

The temperature dependence of the line-shape of H-1 MAS NMR spectra of H-mordenite and H-MCM-22 was examined, Upon raising the temperature of measurements stepwise from 298 to 503 K, the line-width of H-1 MAS NMR of acidic protons in H-mordenite with SiO2/Al2O3 ratio of 106 increased, went through a maximum, and then decreased. This temperature dependence of the spectrum was explained by the thermal motion of protons. The activation energy of the thermal motion was 28 +/- 2 kJ/mol. On the other hand, the temperature dependence of the line-width due to acidic protons in H-mordenite with SiO2/Al2O3 ratios of 19 and 40 and in H-MCM-22 with SiO2/Al2O3 ratio of 31 was much less pronounced. These results indicate that the mobility of protons in these zeolites is lower than that in H-mordenite with SiO2/Al2O3 ratio of 106. (C) 1998 Elsevier Science B.V. All rights reserved.