RELATIONSHIP BETWEEN THE STATE OF PLATINUM AND RESISTANCE OF PT AL2O2CATALYSTS TO POISONING WITH SO2 IN REACTIONS OF CO WITH O-2 OR NO/

The reactions of CO oxidation and NO reduction occur on the surface of platinum particles of different types. The smallest particles are mos t efficient for NO reduction, whereas the largest particles are most a ctive in CO oxidation. Different effects of SO2 on these reactions is due to a difference in the sizes of active sites. The loss of activity in CO oxidation results from a change in the charge state of the plat inum surface atoms in the presence of SO2. The loss of activity in NO reduction is due to the dominant blocking of the small platinum partic les by the surface complexes of SO42-.