Molecular oxygen induced crystallite size effect in reduction of nitric oxide with ammonia ober supported platinum

The effect of changing platinum crystallite size from 2.7 to 15.5 nm on the specific catalytic activity in NO reduction by NH 3 , with and without added O 2 , was studied over alumina supported platinum catalysts between 423 and 473°K. In the NO‐NH 3 system both specific catalytic activity and selectivity to N 2 are independent of crystallite size. In the NO‐O 2 ‐NH 3 system the specific catalytic activity of the 15.5 nm crystallites is about six times that of the 2.7 nm crystallites. The NO reduction rate shows dependence on NO to the first power and on NH 3 to the one‐half power.