Strong Size Effects in Supported Ionic Nanoparticles: Tailoring the Stability of NO x Storage Catalysts
- PDF / 767,570 Bytes
- 8 Pages / 595.276 x 790.866 pts Page_size
- 57 Downloads / 161 Views
Strong Size Effects in Supported Ionic Nanoparticles: Tailoring the Stability of NOx Storage Catalysts Aine Desikusumastuti Æ Mathias Laurin Æ Markus Happel Æ Zhihui Qin Æ Shamil Shaikhutdinov Æ Jo¨rg Libuda
Received: 7 August 2007 / Accepted: 2 November 2007 / Published online: 20 November 2007 Ó Springer Science+Business Media, LLC 2007
Abstract Based on a well-defined model-catalyst approach, we study the particle size dependent properties of NOx storage materials. The single-crystal based model systems are prepared on an ordered Al2O3 film, on which BaO nanoparticles are grown under ultrahigh-vacuum (UVH) conditions. Particle size and density are characterized by scanning tunneling microscopy (STM). The interaction with NO2 is probed by molecular beam (MB) methods in combination with time-resolved IR reflection absorption spectroscopy (TR-IRAS). It is found that both, the stability and the formation kinetics of alumina supported barium nitrate nanoparticles show a strong dependence on particle size. Very small BaO particles are rapidly converted into nitrates, however, the resulting aggregates exhibit a strongly reduced thermal stability. Surface and bulk nitrate and nitrate features are identified by means of vibrational spectroscopy. It is concluded that the size dependencies are related to the formation and decomposition of surface-related BaNOx species the decomposition temperature of which can be tuned over an exceptionally large temperature interval. It is suggested that the stability of these surface NOx species is strongly modified by the underlying support. A. Desikusumastuti M. Laurin M. Happel J. Libuda (&) Lehrstuhl fu¨r Physikalische Chemie II, Universita¨t ErlangenNu¨rnberg, Egerlandstr. 3, 91058 Erlangen, Germany e-mail: [email protected] Present Address: M. Laurin Research Centre for Spectrochemistry, The University of Tokyo, Hongo, Tokyo 113-0033, Japan Z. Qin S. Shaikhutdinov Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
Keywords Supported model catalysts NSR catalysts Barium oxide Nitrogen dioxide Particle size effects IR reflection absorption spectroscopy Scanning tunneling microscopy
Tailoring selectivity and activity of catalyst materials by controlled nanostructuring is a future vision in heterogeneous catalysis. At the purely empirical level, catalyst structures are optimized by varying preparation procedures and conditions, however, from a fundamental point of view, the underlying effects, which control the reaction kinetics and, therefore, the catalytic performance are poorly understood [1, 2]. It is well accepted that for many catalytic reaction systems the size of the catalysts particles is a critical parameter. Traditionally, size effects have been mainly discussed in connection with catalytically active metal particles (see e.g. [3, 4]). In recent works, ionic nanoparticles (mainly oxides) also showed pronounced size dependent effects as well, although the physical origins of these effects may be entirely d
Data Loading...
