A new method for preparing supported catalysts, in which Pt was distributed in locally high concentrations on the gamma-Al2O3 Support, was studied. These catalysts were compared with a conventionally prepared Pt/gamma-Al2O3 catalyst in which Pt was deposited evenly on the support. The object was to ascertain whether it is possible to prepare catalysts that retain heat released from exothermic reactions to a higher extent and thereby become more low-temperature active than a conventionally prepared catalyst. A significant improvement of the activity was observed for the catalysts prepared with locally high Pt concentrations when CO (1%, 1000 and 100 ppm) was oxidized at a constant O-2 concentration (10%). The improved activity is discussed in terms of heat transfer, mass transfer, and structure sensitivity. Differences in heat transfer appear to be the least probable reason for the enhanced activity for the catalysts with locally higher Pt concentrations, whereas structural effects also seem to be an unlikely explanation. Differences in mass transfer seem, however, to be a more likely reason for the improved activity. (C) 2003 Elsevier Inc. All rights reserved.