AVS 45th International Symposium
    Applied Surface Science Division Monday Sessions
       Session AS-MoP

Paper AS-MoP11
X-ray Photoelectron Spectroscopy of Ru@sub 3@(CO)@sub 9@(MeCN)@sub 3@ Modified Platinum Surfaces

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Aspects of Applied Surface Science Poster Session
Presenter: C.R. Cabrera, University of Puerto Rico
Authors: C.R. Cabrera, University of Puerto Rico
E.R. Fachini, University of Puerto Rico
Correspondent: Click to Email
The ability to tailor surfaces is important in electrocatalysis. Furthermore, the interest in obtaining clean energetic systems has driven an additional effort on developing novel catalysts for fuel cells. An extensive study is being made with bimetallic Pt/Ru catalyst for methanol oxidation. This is because it combines the ability of platinum to oxidize methanol and the capacity of ruthenium to decrease the CO poisoning of the electrode surface. Different methods have been proposed to achieve the most economical way to prepare bimetallic catalyst. In the present work, we present a way to modify Pt surfaces with a Ru cluster by using surface organometallic coordination. The cluster used in our experiment is Ru@sub 3@(CO)@sub 9@(MeCN)@sub 3@ (1 mmol in CH@sub 2@C@sub l2@) (I). This cluster was used to modify a platinum foil (99.9%). The cluster (I) was sinthetized from Ru@sub 3@(CO)@sub 12@ (II) following a procedure presented by Aime et al..@footnote 1@ The purity and characterization of the product was confirmed by IR. The modified cluster (I) adsorbs on Pt surface, however, the original cluster, Ru@sub 3@(CO)@sub 12@, was unable to coordinate. The amount of platinum oxides on the surface did not seem change the amount of adsorption of the clusters, even when the platinum surface had a complete oxide layer. The platinum oxide was obtained by electrochemical procedures@footnote 2@ and the amount of oxides was quantified by XPS. Despite of this, a very clean surface (certified by hydrogen adsorption on a CV of H@sub 2@SO@sub 4@ (0.5M)) was required to obtain good reproducibility on the adsorption of (I). After this, a reductive treatment was made by exposing the modified surface a H2 atmosphere: 400@super o@C at 15 min. was enough for the total reduction of the cluster to metallic Ru , either on a platinum surface or in crystalline form (this finding was confirmed by absence of CO and CN stretches in IR measurements). The presence of ruthenium at the platinum surface and its chemical environment was monitored very carefully by XPS analysis. This is necessary because Ru 3d peak overlaps with C 1s transition and is the unique signal for Ru chemical analysis by XPS.@footnote 3@ The binding energy of Ru were 281.7 ± 0.1 eV (cluster on Pt surface) and 280.3 ± 0.2 eV (Ru peak after H@sub 2@ reduction and corresponds to metallic Ru). No peak for Ru oxides was observed. The platinum presented peaks at 71.1 ± 0.2 eV (metallic Pt without Pt oxides), 71.9 ± 0.3 eV (metallic Pt when Pt oxides were present) and a single peak for Pt oxide at 74.7 eV. Just one peak for metallic platinum appeared after the reduction with H@sub 2@. The migration of the Ru atoms into Pt substrate was minimum or inexcistant because with a slight sputtering with Ar was able to eliminate the Ru XPS peak. @FootnoteText@ @footnote 1@ S. Aime, W. Dastr, R. Gobetto, J. Krause, L. Violano, Inorg. Chim. Acta, 235, 357 (1995). @footnote 2@ J.S. Hammond, N. Winograd, J. Electroanal. Chem. 78, 55 (1977). @footnote 3@ J.R. Felthouse, P.B. Framdorf, R.M. Friedman, C.L. Schoesser, J. Catal. 157, 421 (1991).