Catalytic reduction of NO by CO over supported Pd catalysts: effect of the thermal treatments

The catalytic activity of Pd(7%)/Al2O3, Pd(7%)/La2O3-Al2O3, Pd(0.5%)/(20%)CeTbOx/La2O3-Al2O3 and Pd(0.5%)/(40%)CeTbOx/La2O3-Al2O3 catalysts was studied using the reduction of NO by CO at 200°C, employing the pulse technique. Test of temperature programmed reduction (TPR) were carried out on the catalysts after being submitted to different thermal treatments and further reaction. TPR results showed the presence of different sizes of Pd particles. Appreciable changes over the reducible superficial species were reported when the catalysts were subjected to different thermal treatments. Catalysts were active for the NO reduction; however, in all cases low yield of nitrogen was obtained. Pd(7%)/La2O3-Al2O3 catalyst presented the highest conversion under the different reaction conditions, indicating that high palladium loading and a textural promoter (La2O3) favor the reduction of NO by CO. The initial injection of CO or NO and the thermal treatments caused a significant difference in the conversion, affecting the nature of the reducible superficial species. The CO saturation followed by the NO injection enhanced the catalytic activity. The reduction at 300°C and further reaction was the treatment that generated a more active surface.