LASER-SUPPORTED HIGH-TEMPERATURE MAS NMR FOR TIME-RESOLVED IN-SITU STUDIES OF REACTION STEPS IN HETEROGENEOUS CATALYSIS

The temperature of zeolite samples containing various adsorbed molecul es was rapidly changed (within 15 s) from room temperature to 600 K by means of a laser beam. The location of the sealed glass ampoule in a boron nitride container decreases the temperature gradient in the samp le and avoids laser-induced reactions. The technique facilitates time- dependent magic-angle-spinning (MAS) NMR spectroscopy of high-temperat ure reactions which take place within 60 s. The H-D exchange in the hy drogen form of zeolites loaded with fully deuterated molecules, the me thanol-to-gasoline conversion and the catalytic ethylbenzene dispropor tionation in zeolites were monitored by C-13 and H-1 MAS NMR by means of a ''stop and go'' method.