TEMPERATURE-SWITCHED MAS NMR - A NEW METHOD FOR TIME-RESOLVED IN-SITU STUDIES OF REACTION STEPS IN HETEROGENEOUS CATALYSIS

The temperature of zeolite samples containing adsorbed methanol molecules was switched from room temperature to 500-600 K within 30-40 s by means of a laser beam. The catalytic reaction was monitored by C-13 MAS NMR and H-1 MAS NMR, the latter in steps of one second. A two-dimensional Fourier-transformation of the difference between the time-dependent and the equilibrium state of the system gives a good representation of reaction steps. For the methanol conversion it was found that the primarily formed C-3/C-4 alkanes are still involved in further reactions, whereas methane is an inert product under these conditions.