Enhanced Low Temperature NO x Reduction Performance Over Bimetallic Pt/Rh–BaO Lean NO x Trap Catalysts

Abstract

The overall NSR operation was tested over a bimetallic Pt/Rh–BaO lean NOx trap (LNT) catalyst in the range of 473–673 K with simulated diesel exhausts and compared to monometallic 1 wt% Pt/BaO/γ-Al2O3 and 0.5 wt% Rh/BaO/γ-Al2O3 samples. The results showed the beneficial effect of the simultaneous presence of 0.5 wt% Pt and 0.25 wt% Rh on the catalytic performance under lean-burn conditions at low temperatures. It was observed that both Pt/BaO/γ-Al2O3 and Rh/BaO/γ-Al2O3, which both were mildly aged, have limited NOx reduction capacity at 473 K. However, combining Pt and Rh in the NOx storage catalyst assisted the NOx reduction process to occur at lower temperatures (473 K). One possible reason could be that the combined Pt and Rh sample was more resistant to aging. In addition, the NO2-TPD data showed that the presence of Rh into the Pt/BaO/γ-Al2O3 system has a considerable effect on the spill-over process of NOx, accelerating the release of NOx at lower temperatures. These results were in a good agreement with the observed higher rate of oxygen release of the bimetallic Pt/Rh catalyst, leaving a significant number of noble metal sites available for adsorption at lower temperatures than that of the monometallic Pt sample. The superior NSR performance of the bimetallic Pt/Rh/BaO/γ-Al2O3 catalyst under lean-burn conditions suggested the existence of synergetic promotion effect between the Pt and Rh components, increasing the NOx reduction efficiency in comparison with that of the monometallic Pt and Rh–BaO LNT catalysts.