NO-CO reaction kinetics on Pd/MgO model catalysts: morphology and support effects

Citation
L. Piccolo et Cr. Henry, NO-CO reaction kinetics on Pd/MgO model catalysts: morphology and support effects, J MOL CAT A, 167(1-2), 2001, pp. 181-190
Citations number
32
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
ISSN journal
13811169 → ACNP
Volume
167
Issue
1-2
Year of publication
2001
Pages
181 - 190
Database
ISI
SICI code
1381-1169(20010220)167:1-2<181:NRKOPM>2.0.ZU;2-F
Abstract
The NO-CO reaction kinetics has been studied on Pd/MgO (1 0 0) model cataly sts at low pressure by a pulsed molecular beam technique. The model catalys ts have been prepared by epitaxial growth of metal clusters in UHV on cleav ed MgO single crystals. Three samples with mean clusters sizes of 2.8, 6.9 and 15.6 nm have been studied. The reaction products are mainly N-2 and CO2 . The steady-state reaction rate has been measured between 150 and 400 degr eesC at low pressures (10(-9)-10(-6) Torr). The rate limiting step for the reaction is the dissociation of NO at low temperature and the adsorption of CO at high temperature. The reaction probability of NO has been accurately determined, taking into account the reverse spillover of NO from the MgO s upport towards the Pd particles. It is shown that in these conditions the t urnover number is not an appropriate parameter to determine the intrinsic e ffect of particle size. The intrinsic activity depends not only on particle size but also on particle shape. The medium sized particles exhibiting mai nly (1 1 1) facets are found to be more active. The largest particles, whic h exhibit principally (1 0 0) facets, are less active. (C) 2001 Elsevier Sc ience B.V. All rights reserved.