INSITU SOLID-STATE NMR INVESTIGATION OF CRACKING REACTIONS ON ZEOLITE HY

In situ 13C solid-state NMR spectroscopy was used to monitor the cracking of propene oligomers on zeolite HY at elevated temperatures. Experiments were performed in sealed magic-angle spinning rotors, the temperatures of which were cycled between ambient and 503 K. At the upper temperature, the oligomers cracked to form branched butanes, pentanes, and other alkanes. The driving force for this reaction was the formation of highly aromatic coke. These products remained after the catalyst temperature was reduced to ambient. Although olefins are observed in the product stream from cracking in flow reactors, they did not accumulate in detectable quantities in the in situ NMR experiment. We conclude that olefins are unstable with respect to conjunct polymerization for long reaction times on zeolite HY at 503 K. The results of this study are consistent with the view that coke formation can be important in hydrogen-transfer reactions during cracking. © 1990.