Support Dependence of MeOH Decomposition Over Size-Selected Pt Nanoparticles
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Support Dependence of MeOH Decomposition Over Size-Selected Pt Nanoparticles Jason R. Croy Æ Simon Mostafa Æ Jing Liu Æ Yongho Sohn Æ Helge Heinrich Æ Beatriz Roldan Cuenya
Received: 1 July 2007 / Accepted: 30 July 2007 / Published online: 15 August 2007 Ó Springer Science+Business Media, LLC 2007
Abstract We present here the decomposition of methanol over Pt nanoparticles supported on a series of oxide powders. The samples tested may be roughly grouped in two categories consisting of large (*15–18 nm) and small (*8–9 nm) Pt particles deposited on reducible (CeO2, TiO2) and non-reducible (SiO2, ZrO2, Al2O3) supports. The smallest particles (*8 nm), deposited on ZrO2, were found to be cationic and the most active for the decomposition of methanol. Furthermore, the stability of metallic Pt and its oxides was observed to be dependent on the choice of support. In all Pt containing samples the reaction proceeds via he direct decomposition of methanol, as no significant amounts of by-products were detected in the experimental range of 100–300 °C. Keywords Pt nanoparticles Oxide supports Methanol CeO2 TiO2 ZrO2 SiO2 Al2O3 XPS AFM TEM Mass flow reactor
1 Introduction Methanol (MeOH) as a chemical commodity has become a staple of the modern world. Consequently, the synthesis of MeOH has long been an important topic and there is today a preferred catalytic system in wide-spread industrial use (Cu/ZnO/Al2O3) [1]. In the reverse direction, the 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] J. Liu Y. Sohn H. Heinrich Center of Advanced Materials Processing and Characterization, University of Central Florida, Orlando, FL 32816, USA
decomposition of MeOH has increased in significance due to its applicability as a storage fuel for hydrogen and subsequent use in fuel cells. In addition, methanol’s adaptability to the existing infrastructure (i.e. as a liquid fuel) makes the direct methanol fuel cell (DMFC) an attractive technology for transportation applications [2]. There are several decomposition processes currently in use and under study including direct decomposition, steam reforming, and oxidation [3]. These processes require the use of metallic nanoparticle catalysts such as Cu, Pt, and Pd supported on various oxides [4]. However, because a fundamental knowledge of these processes is still lacking, MeOH decomposition and combustion are still subjects of intense studies [5], as is the interaction of MeOH with surfaces relevant to electro-oxidation for fuel cell technologies [6–10]. There is a current debate in the literature on whether metallic Pt or Pt oxides are the most catalytically active species. As an example, PtO2(1 1 0) surfaces have been found more reactive than metallic Pt for CO oxidation [11]. Dam al. [12] have shown that Pt dissolution in fuel cells reaches a saturation level due to the presence of a protective platinum oxide layer, and Hull et al. [13] showed enhanced
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