10980
J. Am. Chem. Soc. 1998, 120, 10980-10981
Dimerization of 1,3-Butadiene on Highly
Characterized Hydroxylated Surfaces of Ultrathin
Films of γ-Al2O3
Michelle M. Ivey, Heather C. Allen, Armen Avoyan,
Kathryn A. Martin, and John C. Hemminger*
Department of Chemistry and Institute
for Surface and Interface Science
UniVersity of California
IrVine, California 92697
ReceiVed July 13, 1998
We describe here the dimerization of 1,3-butadiene to form
4
-vinyl-cyclohexene on highly ordered hydroxylated ultrathin
films of γ-Al . High surface area, powdered γ-Al is widely
used as a catalyst and catalyst support. In addition, there is
interest in the chemistry of Al particulates which exist in the
troposphere. In contrast to the less reactive and more stable
O
2 3
2 3
O
2
O
3
R-Al
2
O
3
, which is available in macroscopic single crystal form,
γ-Al
2
3
O is usually only available in powdered form. Thus, it
has been difficult to study the details of the surface chemistry of
this chemically important phase of Al using the powerful
2
O
3
methods of modern surface sensitive spectroscopy. There are
Figure 1. HREELS vibrational spectrum of a hydroxylated γ-Al
ultrathin film which was grown on a NiAl(100) surface by a 100 L
exposure of H O to the surface as it was held at 900 K. The inset shows
2 3
O
many examples of careful surface science studies of thin films
2 3
of Al O
grown on aluminum and other metal substrates.1
-7
2
Surface science techniques have also been used to characterize
a blow-up of the O-H stretching region of the spectrum.
8
-15
the reactive sites and the chemistry on powdered samples.
Recently, Libuda et al.16 and Gassmann et al. have shown that
ultrathin films of highly ordered γ-Al can be grown on
substrates of NiAl(110) and NiAl(100). Using their methods,
essentially single crystalline films of γ-Al can be prepared
17
spectrometry (LD-FTMS) to study the chemistry of 1,3-butadiene
adsorbed on these ultrathin films of non-hydroxylated and
2 3
O
hydroxylated γ-Al
demonstration of the generation of highly characterized hydroxyl
species on structurally characterized ultrathin films of γ-Al
2 3
O . To our knowledge, this is the first
2
O
3
which are 10-15 Å in thickness. Such ultrathin films are
sufficiently thin to allow characterization by conventional surface
electron spectroscopies and electron diffraction without complica-
tions due to charging which occur when working with bulk
samples of such electrically insulating materials.
2 3
O
and the first observation of the dramatic differences in surface
chemistry which can be caused by surface hydroxyls on these
ultrathin films. 1,3-Butadiene has recently been added to the
California Air Toxics list as the cause of increases in leukemia
16
We have extended the methods of Libuda et al., and
17
and certain types of cancers which can result from chronic
Gassmann et al. to prepare not only highly characterized surfaces
of γ-Al , but also to prepare hydroxylated γ-Al ultrathin
exposure.1
8,19
The chemistry of 1,3-butadiene on the surfaces of
2
O
3
2 3
O
Al O particulates, which are known to exist in the troposphere,
2
3
films. These films can be characterized by low energy electron
diffraction (LEED) for structure, Auger electron spectroscopy
is one piece of the development of a complete picture of the
eventual fate of butadiene which is emitted by industrial sources.
Figure 1 shows the vibrational spectrum (HREELS) of a
γ-Al O ultrathin film with a hydroxylated surface which was
2 3
grown on a NiAl(100) substrate. This spectrum was obtained
with an LK 2000 HREELS spectrometer in an ion-pumped
(AES) for elemental composition, and high-resolution electron
energy loss spectroscopy (HREELS) for vibrational spectra. We
report here the use of laser desorption Fourier transform mass
(
1) Crowell, J. E.; Chen, J. G.; Yates, J. T., Jr. Surf. Sci. 1986, 165, 37.
2) Chen, J. G.; Crowell, J. E.; Yates, J. T., Jr. Phys. ReV. B 1986, 33,
(
-10
ultrahigh vacuum chamber with a base pressure of 1 × 10
1
436.
-
1
(
3) Street, S. C.; Guo, Q.; Xu, C.; Goodman, D. W. J. Phys. Chem. 1996,
Torr. The vibrational modes at 899, 702, 592, and 416 cm are
the γ-Al O phonons. The mode at 1797 cm , and the low
2 3
1
00, 17599.
-1
(
(
(
(
4) Wu, M.-C.; Goodman, D. W. J. Phys. Chem. 1994, 98, 9874.
5) Goodman, D. W. J. Vac. Sci. Technol. A 1996, 14, 1526.
6) Wu, Y.; Garfunkel, E.; Madey, T. E. Surf. Sci. 1996, 365, 337.
7) Wu, Y.; Garfunkel, E.; Madey, T. E. J. Vac. Sci. Technol. A 1996, 14,
-1
-1
intensity modes at ∼1500 cm and ∼1100 cm are combination
modes of the phonons. The narrow widths of the phonon peaks
are limited by the spectrometer resolution in these experiments
and are indicative of the highly ordered nature of the oxide film.
The mode at 3675 cm shown in the inset of Figure 1 is the OH
stretching mode of the surface hydroxyl groups. This mode is
extremely narrow when compared to the corresponding OH
2
554.
(
8) Beebe, T. P., Jr.; Crowell, J. E.; Yates, J. T., Jr. J. Chem. Phys. 1990,
-
1
9
2, 5519.
(
9) Ballinger, T. H.; Yates, J. T., Jr. Langmuir 1991, 7, 3041.
(
10) Ballinger, T. H.; Smith, R. S.; Colson, S. D.; Yates, J. T., Jr. Langmuir
1
992, 8, 2473.
2 3
stretching mode seen for hydroxyl groups on Al O powdered
(
(
(
(
11) Coustet, V.; Jupille, J. Surf. Sci. 1994, 307-309, 1161.
12) Kn o¨ zinger, H. Angew. Chem., Int. Ed. Engl. 1968, 7, 791.
13) Liu, X.; Truitt, R. E. J. Am. Chem. Soc. 1997, 119, 9856.
14) Fleisch, T. H.; Meyers, B. L.; Hall, J. B.; Ott, G. L. J. Catal. 1984,
samples.13 The OH stretching mode frequency which we observe
is characteristic of isolated OH groups on the surface which are
bonded to three Al sites.20 Identical spectra can be obtained by
8
6, 147.
15) Baker, B. G.; Jasieniak, M. In Surface Science. Principles and current
(
applications.; MacDonald, R. J., Taglauer, E. C., Eds.; Springer-Verlag: Berlin,
996.
16) Libuda, J.; Winkelmann, F.; B a¨ umer, M.; Freund, H.-J.; Bertrams,
T.; Neddermeyer, H.; M u¨ ller, K. Surf. Sci. 1994, 318, 61.
17) Gassmann, P.; Franchy, R.; Ibach, H. Surf. Sci. 1994, 319, 95.
(18) Ward, E. M.; Fajen, J. M.; Ruder, A. M.; Rinsky, R. A.; Halperin, W.
E.; Fessler-Flesch, C. A. Toxicology 1996, 113, 157.
1
(
(19) Macaluso, M.; Larson, R.; Delzell, E.; Sathiakumar, N.; Hovinga, M.;
Julian, J.; Muir, D.; Cole, P. Toxicology 1996, 113, 190.
(
(20) Kn o¨ zinger, H.; Ratnasamy, P. Catal. ReV.-Sci. Eng. 1978, 17, 31.
1
0.1021/ja982449m CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/09/1998