Pt black was exposed to trans-trans-2,4-hexadiene at two different pressures at 603 K. The surface composition and valence state of carbon upon carbonization and after regeneration were monitored by XPS. Exposure to hydrocarbon 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 activity in test runs with n-hexane + H-2 was 8-12% of that of the regenerated 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 under the effect of H-2 in the test mixture was also slower in the latter case. (C) 2001 Elsevier Science B.V. All rights reserved.