Pt black was exposed to trans-trans-2,4-hexadiene at two different pressure
s at 603 K. The surface composition and valence state of carbon upon carbon
ization and after regeneration were monitored by XPS. Exposure to hydrocarb
on brought about mainly accumulation of contiguous carbon: graphite as well
as CxHy polymers. Less than half of this carbon was removed by O-2 and H-2
. "Atomic C" was more abundant after regeneration. The residual catalytic a
ctivity in test runs with n-hexane + H-2 was 8-12% of that of the regenerat
ed catalyst. Slightly more graphite and/or polymeric carbon after exposure
at higher hexadiene pressure caused a more severe deactivation, manifesting
itself mainly in shifting the selectivities. Partial self-regeneration und
er the effect of H-2 in the test mixture was also slower in the latter case
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