Enhanced reactivity of Pt nanoparticles supported on ceria thin films during ethylenedehydrogenation

Abstract

The adsorption and reaction of ethylene on Pt/CeO_2−x/Cu(111) model catalysts were studied by means of high resolution photoelectron spectroscopy (HR-PES) in conjunction with resonant photoemission spectroscopy (RPES). The dehydrogenation mechanism is compared to the HR-PES data obtained on a Pt(111) single crystal under identical conditions. It was found that the Pt nanoparticle system shows a substantially enhanced reactivity and several additional reaction pathways. In sharp contrast to Pt(111), partial dehydrogenation of ethylene on the supported Pt nanoparticles already starts at temperatures as low as 100 K. Similar to the single crystal surface, dehydrogenation occurs via the isomer ethylidene (CHCH₃) and then mainly viaethylidyne (CCH₃). In the temperature region between 100 and 250 K there is strong evidence for spillover of hydrocarbon fragments to the ceria support. In addition, splitting of ethylene to C₁ fragments is more facile than on Pt(111), giving rise to the formation of CH species and CO in the temperature region between 250 and 400 K. Upon further annealing, carbonaceous deposits are formed at 450 K. By heating to 700 K, these carbon deposits are completely removed from the surface by reaction with oxygen, provided by reverse spillover of oxygen from the ceria support.