In situ Fourier Transform Infrared Studies of Active Sites and Reaction Mechanisms in Heterogeneous Catalysis: Hydrocarbon Conversion on H-Zeolites

Abstract

Adsorption of CO at -180 DegC and pyridine at 150 DegC shows that a dealuminated HY zeolite prepd. by hydrothermal treatment at 550 DegC followed by mild acid leaching presents Lewis acid sites, due to extra-framework aluminum debris, and very strong Bronsted acid sites (Ho .apprx. -12), characterized by an IR band at 3600 cm-1. Use of an IR cell as a flow reactor shows that these hydroxyl groups are active sites for n-hexane cracking at 400 DegC, whereas an HY zeolite dealuminated by isomorphous substitution is almost inactive under the same conditions. GC anal. of the products formed indicates that cracking occurs through a protolytic mechanism. All the results obtained show that the IR cell designed for flow expts. can be used as a conventional reactor. [on SciFinder (R)]