ROLES OF SUPPORTS, PT LOADING AND PT DISPERSION IN THE OXIDATION OF NO TO NO2 AND OF SO2 TO SO3

Three types of platinum catalysts, Pt/SiO2, Pt/gamma-Al2O3 and Pt/ZrO2 were examined for the oxidation of NO to NO2 and of SO2 to SO3. The a ctivity order for both oxidation reactions was found to be: Pt/SiO2 > Pt/gamma-Al2O3 > Pt/ZrO2. The effect of Pt loading and Pt dispersion o n the catalytic activity and selectivity was examined. Over Pt/SiO2, t he specific activities were found to be strongly size-dependent, the l arger Pt particles exhibiting higher specific activity than the smalle r ones. Over the Pt/gamma-Al2O3 catalysts, however, the size-dependenc e appeared to be much less significant than that of the Pt/SiO2 cataly sts. The results for Pt/ZrO2 catalysts, however, showed that the speci fic activities for both reactions were most probably size-independent. The catalytic selectivity for the oxidation of NO relative to that of SO2 appeared to be size-independent for all the catalysts, The intera ction of NO, NO2 and SO2 with the catalysts and the effect of the supp ort on the interaction were investigated using TPD technique.