Variable temperature 1H MAS NMR:: A powerful tool for the investigation of dynamic properties of acidic protons in zeolites and heteropoly compounds

The dynamic nature of the protons in zeolites such as H-ZSM-5, metallosilicates molecular sieves and heteropoly compounds was examined by temperature dependence of 1H MAS NMR in the range of 298 and 473K. The temperature-dependent lineshape of 1H MAS NMR spectra of acidic protons in zeolites showed the first and unambiguous evidence for proton migration in zeolite structure. The dynamic property of protons was a more sensitive measure for the activity of protons than the static parameters such as NMR chemical shifi and I R band position of OH bonds. The temperature-dependent 1H MAS NMR also revealed the mobility of protons in heteropoly compounds (H3PWI2O40 Ag3PW12O40 and palladium metal loaded on H3PW12O40). This method gave the information of the dynamical process between protons and hydrogen molecules in the gas phase. The variable temperature 1H MAS NMR is a very useful technique for understanding dynamic properties of protons in solid acids The dynamic property is an important factor infiuencing the catalytic activity of a solid acid catalyst. The various experimental facts described above show that the temperature variable 1H MAS NMR could reveal the dynamics of protons in solid acids. Information obtained by this technique offers new insights, which could not be obtained by other means, on the acidic properties of solid acids and their catalysis. The significance of proton mobility in catalysts will be able to be discussed in the future. © 1999 Academic Press.