Influence mechanism of Pd, Pt, Rh/γ-Al2O3 on NH3 formation for NO reduction by CO

The byproducts of NO reduction by CO have attracted great interest in the three-way catalysts, but the influence of active components (Pd, Pt, and Rh) on the formation mechanism is still elusive. Herein, Pd/, Pt/, and Rh/Al2O3 were prepared for investigating the NH3 formation during NO reduction by CO under wet conditions. The strongest metal-support interaction in Rh/Al2O3 is attributed to the highest interfacial Rh–O–Al bond from the results of XAFS and NMR. The smallest particle size and highest redox property on Rh/Al2O3 led to the highest NH3 yield below 300 °C. Pt/Al2O3 produced more NH3 than Pd/Al2O3 above 350 °C because of robust response to lattice oxygen reacted with NO and reduction by CO. The optimal strategy for minimizing byproducts on the premise of preserving three-way catalyst performance was the PtRh/γ-Al2O3 where the molar ratio of Pt: Rh was 9:1.