PtRu Colloid Nanoparticles for CO Oxidation in Microfabricated Reactors
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Catalysis Letters Vol. 109, Nos. 1–2, June 2006 (Ó 2006) DOI: 10.1007/s10562-006-0050-x
PtRu colloid nanoparticles for CO oxidation in microfabricated reactors Asbjørn Klerke,a Souheil Saadi,b Maja Bøg Toftegaard,a Anders Theilgaard Madsen,a Jane H. Nielsen,b Søren Jensen,c Ole Hansen,b,c Claus Hviid Christensen,a and Ulrich J. Quaadeb,* a
Danish National Research Foundation’s Center for Sustainable and Green Chemistry (CSG), Department of Chemistry, Technical University of Denmark, 2800 Kgs Lyngby, Denmark b Danish National Research Foundation’s Center for Individual Nanoparticle Functionality (CINF), Department of Physics, Technical University of Denmark, 2800 Kgs Lyngby, Denmark c MIC – Department of Micro and Nanotechnology, Technical University of Denmark, 2800 Kgs Lyngby, Denmark
Received 15 December 2005; accepted 1 March 2006
The catalytic activity of PtRu colloid nanoparticles for CO oxidation is investigated in microfabricated reactors. The measured catalytic performance describes a volcano curve as a function of the Pt/Ru ratio. The apparent activation energies for the different alloy catalysts are between 21 and 117 kJ/mol, which agree well with literature. The size distribution of the colloid nanoparticles is determined from STM and TEM, from which an average size of the colloid nanoparticles of 2.2±0.5 nm is determined. KEY WORDS: CO oxidation; heterogeneous catalysis; nanoparticles; colloids; alloyed nanoparticles; platinum and ruthenium.
1. Introduction Selective CO oxidation is an important reaction when hydrogen is produced by steam-reforming of hydrocarbons for use in proton exchange membrane fuel cells (PEMFC) since the common anodic catalyst in PEMFC is severely poisoned by CO even in minute quantities [1, 2]. This deactivation of the anodic catalyst can be avoided if CO is completely oxidized to CO2 because the anode tolerance for CO2 is much higher than it is for CO. Several different catalysts have been proposed for the selective catalytic oxidation of CO, for example metal oxides [3, 4] and noble metals [5, 6] with a special emphasis on platinum and ruthenium [7–10]. This special interest in Pt and Ru has been substantiated through theoretical studies of CO desorption on platinum, ruthenium and an alloy of Pt and Ru [11–13]. The studies show that such an alloy has a significantly lower desorption energy for CO than both of the pure metals. This lower desorption energy gives the possibility of a higher catalytic activity, as CO covering the surface of the catalyst is most probably an important limiting factor for the activity. Here, we report and discuss the use of PtRu alloys for the oxidation of CO in microfabricated reactors. It is found that an easy method for preparing alloys of PtRu is to synthesize colloid nanoparticles [14]. To form these colloids, Pt4+ and Ru3+ precursors are reduced to PtRu colloids in alkaline ethylene glycol solutions where ethylene glycol acts as a reducing agent and a colloid *To whom correspondence should be addressed. E-mail: [email protected]
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