Mn-Fe-Ce multiple oxides with Al2O3 coating supported onto honeycomb cordierite monoliths for NO catalytic oxidation

Abstract

Mn-Fe-Ce multiple oxides with Al2O3 coating supported over honeycomb cordierite monoliths including Mn-Fe-CeOx/Al2O3/HCM and Mn-Fe-CeOx-Al2O3/HCM were optimized and compared for the catalytic oxidation of NO. The addition of Al2O3-coatings increased the specific surface area for more loadings of active components and also making the distribution of active species more uniform. Pseudo-boehmite as coating showed a better enhancement on NO oxidation than nano-Al2O3 coating directly. Whatever Mn-Fe-CeOx/Al2O3/HCM prepared by sol-gel and impregnation methods or Mn-Fe-CeOx-Al2O3/HCM prepared by slurry coating of co-precipitated Mn-Fe-CeOx powders and pseudo-boehmite binders onto HCM, the optimized doping amounts of Mn-Fe-CeOx was 15 wt. % with 10 wt. % Al2O3 for good activity than the impregnated Mn-Fe-CeOx/HCM without Al2O3-coatings. H2-TPR, SEM, XPS, NO + O2-TPD and DRIFTS characterizations showed that the promoted catalytic oxidation activity of NO-to-NO2 via the intermediate nitrate-species over Mn-Fe-CeOx/Al2O3/HCM and Mn-Fe-CeOx-Al2O3/HCM were benefited from more surface concentrations of active oxygen, efficient synergetic interaction between Fe and Mn ions (Fe2+ + Mn4+ ↔ Mn3+ + Fe3+) and high oxidizing ability accelerated by high Ce4+/Ce3+ ratio. Mn-Fe-CeOx-Al2O3/HCM catalyst have the potential advantages of good catalytic activity (74.4 % NO conversion at 250 °C) and appropriate production process (3−4 days of preparation period), which also gave the moderate shedding rate with the shedding modes of internal spalling and interface spalling than Mn-Fe-CeOx/Al2O3/HCM sample.