Impact of the modification of carbon-supported, Pt-based catalysts by irreversibly adsorbed Sn, Ru and Rh on ethanol oxidation

Abstract

The oxidation of ethanol was studied at Snad-, Ruad- and Rhad-modified and unmodified PtC, Pt3Sn/C and Pt3Ru2/C catalysts. Potentiodynamic, quasi-steady-state and chronoamperometric measurements were used to investtigate the activity and stability of the catalysts. Irreversible adsorption of a small amount of each of the adatoms (≈10 % surface coverage) enhanced the activity of the Pt/C and Pt3Sn/C catalysts. The onset potential was shifted by ≈50 mV towards lower values and the current densities over the whole studied potential region were up to two times higher with respect to the unmodified catalysts. On the other hand, the addition of Snad or Rhad slightly increased the activity of Pt3Ru2/C, while the presence of Ruad decreased its activity for ethanol oxidation. The catalytic action of Snad and Ruad was associated mostly with their ability to adsorb oxygen-containing species at lower potentials than Pt, permitting a bifunctional mechanism to proceed. Rhad also acted on the C-C bond breaking activation as well as source of oxygen containing species, increasing in this way the activity of the modified surfaces for ethanol oxidation.

Oksidacija etanola je ispitivana na Pt/C, Pt3Sn/C i Pt3Ru2/C katalizatorima modifikovanim ireverizibilno adsorbovanim Snad, Ruad i Rhad adatomima. Njihova aktivnost i stabilnost ispitivana je potenciodinamičkim, hronoamperometrijskim i kvazi-stacionarnim merenjima. Dobijeni rezultati su pokazali da mala količina ireverzibilno adsorbovanih adatoma (10 %) povećava aktivnost Pt/C i Pt3Sn/C katalizatora. Početak reakcije je pomeren ka negativnijim vrednostima za ≈50 mV i dobijene su oko dva puta veće gustine struje u poređenju sa nemodifikovanim katalizatorima. Dodatak Snad ili Rhad malo povećava aktivnost Pt3Ru2/C katalizatora, dok dodatak Ruad smanjuje njegovu aktivnost za oksidaciju etanola. Katalitička aktivnost adatoma Sn i Ru se uglavnom vezuje sa njihovom sposobnošću da adsorbuju OH čestice na nižim potencijalima od Pt i na taj način poboljšavaju bifunkcionalni mehanizam reakcije. Povećana aktivnost katalizatora modifikovanih adatomima Rh može se objasniti lakšim kidanjem C-C veze u etanolu, kao i povećanom količinom OHad čestica na Rh mestima.