2
3
4
5
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Na cations are present, the total number of protons and the
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product distribution from aromatics to propene. Thus, the
total amount of hydrogen that must be removed from the
surface is much less to form propene than to form a more
unsaturated benzene molecule. Hydrogen selectivities are
similar in all Zn catalysts, but the excess hydrogen that must
be disposed as aromatics are produced in Zn/H-ZSM5 and
Zn/Na-ZSM5 (2.04 wt.%) leads to the unselective removal of
hydrogen, as methane and ethane (Table 2). The propane rate
does not increase linearly with Zn loading in Zn/Na-ZSM5
because less active Zn species are formed and because the
sample contains a higher proton concentration. The higher
proton site density leads to higher propene aromatization
rates, which leads to more H-atoms to be disposed, causing
Zn/Na-ZSM5 to resemble Zn/H-ZSM5.
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2
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3
8
2
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5. Acknowledgements
This work was supported by the National Science Foundation
(CTS-96-13632) and by start-up funds provided by the Uni-
versity of California. X-ray absorption data were collected at
Stanford Synchrotron Radiation Laboratory (SSRL), which is
operated by the Department of Energy (DOE), Office of Basic
Energy Sciences, under contract DE-ACO3-76SF00515. The
authors acknowledge Dr George D. Meitzner (Edge Analyti-
cal, Inc.) for helpful discussions and expert technical assistance
in the analysis of X-ray absorption data.
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