A series of platinum catalysts supported on gamma-alumina and prepared by using a wet impregnation procedure were characterized by hydrogen temperature-programmed desorption and steady-state CO-NO reaction tests. The impregnant pH was the crucial variable in the generation of five catalysts of 0.75-0.87% Pt load at initial pH from 2.15 to 4.65. The impregnant pH showed a clear impact on both hydrogen uptake and catalytic performance. The catalysts prepared under acidic conditions demonstrated a higher catalytic activity than those prepared under basic conditions, while hydrogen adsorption levels were of the same order of magnitude. Activation energies for the CO-NO reaction were found to depend on impregnant pH.