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

Journal Article · Wed Nov 13 23:00:00 EST 1991 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100176a071· OSTI ID:7273922

Lazo, N D; Richardson, B R; Schettler, P D; White, J L; Munson, E J; Haw, J F ^[1]

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1. Texas A and M Coll., College Station (United States)

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

• OSTI ID: 7273922
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:23; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400 -- Petroleum-- Processing
2-METHYLPROPENE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKENES
CARBON 13
CARBON ISOTOPES
CHEMICAL REACTIONS
CHEMICAL SHIFT
DATA
ETHERS
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MATERIALS
MINERALS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
RESONANCE
SILICATE MINERALS
STABLE ISOTOPES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
ZEOLITES