Rhodium has been replaced in a synergistic Pt-Rh/gamma-Al2O3 catalyst for the reduction of NO with H-2 with a less expensive transition metal (Co). Performance in activity and selectivity was still better than Pt alone, thus synergy was again obtained. The nanoparticles in the Pt-Co catalyst were designed and tailored to mimic the microstructure of the synergistic Pt-Rh nanoparticles.