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Zeolite-Catalyzed Isobutene Amination: Mechanism and Kinetics

Journal Article · · ACS Catalysis
 [1];  [1];  [2];  [1];  [1]
  1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States)
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Amination of isobutene with NH3 was researched over Brønsted acidic zeolites at 1 atm and 453-483 K. To compare catalytic activities over different zeolites, the measured reaction rates are normalized by the number of active sites determined by tert-butylamine temperature-programmed desorption (TPD). Small- and medium-pore zeolites with one-dimensional channels exhibit low activity because of pore blockage by adsorbed tert-butylammonium ions. Yet, turnover frequencies and activation energies are not sensitive to framework identity, as long as the active site is accessible to isobutene and tert-butylamine. Kinetic measurements and FTIR spectroscopy reveal that the Brønsted acid sites in MFI are covered predominantly with tert-butylammonium ions under reaction conditions. The desorption of tert-butylamine is assisted by the concurrent adsorption of isobutene. DFT simulations show that at very low tert-butylamine partial pressures, for example, at the inlet to the reactor, tert-butylamine desorption is rate-limiting. However, at sufficiently high tert-butylamine partial pressures (>0.03 kPa), protonation of isobutene to the corresponding carbenium ion limits the rate of amination.
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
National Institutes of Health (NIH); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1572043
Journal Information:
ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 8 Vol. 9; ISSN 2155-5435
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

Figures / Tables (19)

Scheme 1(p. 2)figure Scheme 1
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Table 1(p. 6)table Table 1
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Scheme 2(p. 9)figure Scheme 2
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Related Subjects

2-methylpropene
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
C−N coupling
DFT
MFI
ZSM-5
hydroamination