Metal dispersion of CeO2-ZrO2 supported platinum catalysts measured by H2 or CO chemisorption

The platinum dispersion has been determined by chemisorption of H-2 and CO on a series of ceria-zirconia supported catalysts covering the full range of composition between ceria and zirconia. The quantities were measured by volumetric techniques and by FTIR spectroscopy. Reduction and measurement temperatures were studied in order to fix a specific H-2 chemisorption protocol. The latter is based on the use of double isotherm of hydrogen adsorption at 195 K, this low temperature being required to suppress the hydrogen spillover on the support. The irreversible adsorption measured either at saturation or by extrapolation to zero pressure leads to the most reliable dispersion values, in agreement with those deduced from CO chemisorption at room temperature followed by FTIR spectroscopy, technique which allows to discriminate the adsorption on the platinum surface from that on the ceria-zirconia support. By applying these two methods, it was found that, after reduction at 473 K, platinum dispersion is always higher on the mixed oxides than on the pure ceria or zirconia supports. It was nearly constant at 60-65% for a wide range of composition of the mixed oxide between Ce0.15Zr0.85 and Ce0.68Zr0.32. (C) 2003 Elsevier B.V. All rights reserved.