In situ variable-temperature MAS carbon-13 NMR study of the reactions of isobutylene in zeolites HY and HZSM-5

摘要: The low-temperature chemistry of isobutylene in zeolites HY and HZSM-5 was probed by situ variable-temperature {sup 13}C NMR spectroscopy with magic-angle spinning (MAS). Isobutylene interacts Bronsted acid sites the at a temperature ca. 123 K to form hydrogen-bonded species, as indicated 2{sup 13}{Delta}{delta} value (relative 2-{sup resonance isobutylene) 12 ppm {Delta}{delta} 16 HZSM-5. greater observed for is consistent being more acidic than those HY. maximum number species detected did not exceed zeolites. As raised from K, presumably converted an unobserved symmetrical intermediate (a tert-butylcarbenium ion) that either underwent deprotonation re-form site or reacted another molecule dimer. Evidence this process included scrambling between 1- 3-{sup labels isobutylene. In all spectra obtained cross polarization single-pulse excitation, no peaks were could be assigned surface-bound silyl ethermore » species. However, experiments performed on 2-methyl-2-propanol-2-{sup 13}C/HZSM-5 system, formation tert-butyl ether observed, reported earlier laboratory.« less