Radiotracer and thermal desorption studies of dehydrogenation and atmospheric hydrogenation of organic fragments obtained from [ 14C]ethylene chemisorbed over Pt(111) surfaces

Abstract

The energetics and reversibility of ethylene sequential dehydrogenation on the (111) platinum single crystal surface has been investigated at 300–600 K using thermal desorption spectroscopy and a carbon-14 radiotracer technique. Ethylidyne species produced by [ 14C]C 2H 4 chemisorption at 300–400 K were stable with respect to hydrogenation at room temperature. However, at atmospheric hydrogen pressure and temperatures above 350 K, ethylidyne species were easily eliminated from the platinum surface by hydrogenation. For [ 14C]C 2H 4 adsorption temperatures above 450 K, radiotracer studies revealed the presence of both “active” and “inactive” forms of partially dehydrogenated carbonaceous deposits on the platinum surface which differ greatly in their reactivity for hydrogenation and hydrogen transfer with unlabeled hydrocarbons. The inactive fraction increased with increasing adsorption temperature as the surface species became more hydrogen deficient. Removal of the active 14C-containing species by hydrogen transfer occurred readily.