Ethene adsorption, dehydrogenation and reaction with Pd(110): Pd as a carbon 'sponge'

Michael Bowker*, Chris Morgan, Neil Perkins, Richard Holroyd, Elodie Fourre, Federico Grillo, Alexander MacDowall

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

52 Citations (Scopus)

Abstract

The interaction of ethene with the Pd(110) surface has been investigated, mainly with a view to understanding the dehydrogenation reactions of the molecule and mainly using a molecular beam reactor. Ethene adsorbs with a high probability over the temperature range 130 to 800 K with the low-coverage sticking probability dropping from 0.8 at 130 K to 0.35 at 800 K. The adsorption is of the precursor type, with a weakly held form of ethene being the intermediate between the gas phase and strong chemisorption. Dehydrogenation begins at ∼300 K and is fast above 350 K. If adsorption is carried out at temperatures up to ∼380 K, adsorption saturates after about 0.25 monolayer have adsorbed, but above ∼450 K, adsorption continues at a high rate with continuous hydrogen evolution and C deposition onto the surface. It appears that, in the intermediate temperature range, the carbonaceous species formed is located in the top layer and thus interferes with adsorption, whereas the C goes subsurface above 450 K, the adsorption is almost unaffected, and the C signal is significantly attenuated in XPS. However, the deposited carbon can easily be removed again by reaction with oxygen, thus implying that the carbon remains in the selvedge, that is, in the immediate subsurface region probably consisting of a few atomic layers. No well-ordered structures are identified in either LEED or STM, though some evidence of a c(2×2) structure can be seen. The Pd surface, at least above 450 K, appears to act as a "sponge" for carbon atoms, and this effect is also seen for the adsorption of other hydrocarbons such as acetaldehyde and acetic acid.

Original languageEnglish
Pages (from-to)2377-2386
Number of pages10
JournalJournal of Physical Chemistry B
Volume109
Issue number6
DOIs
Publication statusPublished - 17 Feb 2005

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