Size-selected Pt Nanoparticles Synthesized via Micelle Encapsulation: Effect of Pretreatment and Oxidation State on the
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Size-selected Pt Nanoparticles Synthesized via Micelle Encapsulation: Effect of Pretreatment and Oxidation State on the Activity for Methanol Decomposition and Oxidation Jason R. Croy Æ S. Mostafa Æ H. Heinrich Æ B. Roldan Cuenya
Received: 28 April 2009 / Accepted: 26 May 2009 / Published online: 10 June 2009 Ó Springer Science+Business Media, LLC 2009
Abstract The effect of pretreatment conditions on the oxidation state and activity of micelle-synthesized Pt nanoparticles supported on ZrO2 was studied for methanol decomposition and oxidation reactions. An O2-pretreatment is observed to be effective for producing clean, stable, and active nanoparticles. Pt-oxide species formed during such pretreatments were found to have little influence in methanol decomposition reactions due to their tendency to reduce. However, these same species are stable during methanol oxidation and appear to take part in a Mars-van Krevelen-type of process, in which bound-oxygen (nanoparticle shell) may be replenished with oxygen from the gas phase. Keywords Pt nanoparticles Micelles Methanol decomposition Methanol oxidation Pt oxide PtO PtO2 ZrO2 XPS TEM AFM Mass spectrometry Packed-bed reactor
J. R. Croy S. Mostafa H. Heinrich B. R. Cuenya (&) Department of Physics, University of Central Florida, Orlando, FL 32816, USA e-mail: [email protected] S. Mostafa B. R. Cuenya Department of Civil and Environmental Engineering, University of Central Florida, Orlando, FL 32816, USA H. Heinrich Center of Advanced Materials Processing and Characterization, University of Central Florida, Orlando, FL 32816, USA B. R. Cuenya Nanoscience and Technology Center, University of Central Florida, Orlando, FL 32816, USA
1 Introduction In the last two decades it has become evident that highly dispersed metal nanoparticles (NPs) supported on oxides display unique catalytic properties. Novel geometric as well as electronic effects present in small particles (\10 nm) give rise to the intriguing physical and chemical properties of these systems [1–5]. Furthermore, interaction of the NPs with the support oxide may be significant and likewise contribute to the observed catalytic performance [6–16]. However, one of the major challenges in working with such catalysts is the difficulty in producing highly dispersed NPs with controllable size and spatial distributions. This becomes important in light of the fact that NP size can influence activity [17–20] and selectivity [3] as well as the stability of some metal-oxide species [4, 17, 21, 22], which might themselves present enhanced chemical reactivities [23]. In addition, the favorable reduction of surface energy by an increase in NP size (i.e., thermal sintering) must be minimized during catalysts preparation and subsequent exposure to chemical reactants [24]. This minimization may be facilitated by proper choice of support [7, 25, 26], and/or interparticle distances when using planar substrates [27]. An additional concern is the cleanliness of the catalytically active component (e.
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