Analysis of Dynamics and Molecular Design of Heteropolyacid catalysts by High Resolution Solid State NMR

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"Pseudo-liquid" phase of heteropoly acids, in which reactant molecules are abosrbed into bulk of catalysts, is considered as unique 3-dimensional reaction field. It is noteworthy that proton and hetelopolyanion would contribute catalysis concertedly. In this study, dinamic behavior of adsorbed moelcules in pseudo-liquid phase of heteropolyaced and zeolite were elucidated mainly by high-resolution solid-state NMR experiments.In the pseudo-liquid phase of methanol-H_3PW_<12>O_<40> system, it was elucidated by ^<13>C,^1H,and ^<31>P solid-state NMR that protonated methanol monomerand dimer were formed stoichiometrically when absorbed amounts was varied form 1 molecule/anion to 6 molecules/anion. As for 1-6 molecules/anion, proton of heteropolyacid and hydroxy of methanol exchanged rapidly, while the nobility of methanol molecules was low. Above 6 molecule/anion, sharp peaks were observed by ^1H NMR,demonstrating rapid movement of methanol molecules in pseudo-liquid phase. This is a rare casein which ^1H NMR of solid gave sharp peaks. the significant increase of the mobility when absorbed amount was changed from 6 molecules/anion to 7 molecules/anion indicates high stabilities of protonated methanol monomer and dimer which were formed for 6 molecul/anion or below. On the other hand, only a part of adsorbed methanol was able to interact with proton on H-ZSM-5 at rt. This would be due to the different position of proton sites and acid strength distribution.In addition, methoxy groups, which would be and intermediate of dehydration reaction, were directly observed in pseudo-liquid phase heated up to 423 K by solid state NMR.