| A series of experimental gamma-alumina (a-Al2O3) supported monometallic platinum (Pt), monometallic palladium (Pd), and bimetallic Pt-Pd catalysts were synthesized. The activities of these catalysts for nitrogen monoxide (NO) reduction by hydrogen (H2) were tested. The uncalcined catalysts were more active than their corresponding calcined catalysts. The uncalcined Pd-rich bimetallic catalysts were found to be synergistic and more active than pure Pt catalysts. The average particle sizes of all these catalysts were smaller than 3.5 nm, except that of the calcined Pd-rich catalyst. Nanoparticles observed in calcined catalysts were smaller than those in uncalcined catalysts. Sizes of nanoparticles in pure Pt and Pt-rich catalysts displayed normal distribution, while sizes of nanoparticles in pure Pd and Pd-rich catalysts displayed bimodal distribution. The various catalytic activities of these catalysts are explained by the differences in the sizes and surface compositions of nanoparticles formed in these catalysts. |
