APPLICATIONS OF A NEW CAVERN DESIGN TO THE STUDY OF REACTIONS ON CATALYSTS USING INSITU SOLID-STATE NMR

A new approach to preparing samples for in situ magic-angle spinning (MAS) NMR studies of chemical reactions on catalysts that offers several significant improvements over existing methods is described. This contribution describes the design and use of a second-generation CAVERN apparatus that is easily fabricated from glass and other inexpensive materials. The success rate using this apparatus for preparing reactive catalyst-adsorbate samples for study by MAS NMR is nearly 100%. A second major advantage of this design is that it permits the MAS rotor to be returned to the vacuum line for the adsorption of additional reactants prior to resuming in situ NMR study. The use of the second-generation CAVERN apparatus is illustrated by demonstrating the sequential adsorption feature. The observed induction period in the conversion of methanol to gasoline on HZSM-5 is studied by sequential adsorption of methanol. Although the first aliquot of methanol exhibited a long induction period before hydrocarbon synthesis at 523 K, none was observed following adsorption of a second aliquot, showing that the products have an influence on the observed kinetics. © 1992.