The catalytic performance of Pt impregnated MCM-41 and SBA-15 in selective catalytic reduction of NOx

This study compared the de-NOx performance and surface physical properties of Pt (1.0 wt.%)-impregnated MCM-41(meso-pore) and SBA-15 (meso- and micro-pores) with different frameworks. In the de-NOx reaction, NO reduction occurred from 150 °C with the combustion of a reducing reagent (propylene) in Pt/SBA-15 while it appeared from 200 °C in Pt/MCM-41. The level of conversion reached 80% at 200 °C in the case of Pt/MCM-41 but was decreased rapidly with increasing reaction temperature. Although the level of NO conversion was higher in Pt/SBA-15 (100% conversion) at the lower temperature of 150 °C, it decreased slightly to 83% above 200 °C, which was maintained up to 600 °C. This result was attributed to the differences in the structural dimension between Pt/MCM-41 and Pt/SBA-15 and the adsorption abilities of the reducing agent and NO, as well as the different Pt active species over MCM-41 and SBA-15. The adsorption abilities of NO and the reducing agent (propylene) were definitely higher on Pt/SBA-15 than those on Pt/MCM-41, and was maintained at high temperatures on Pt/SBA-15. XPS suggested that Pt, PtO, and PtO2 play a role as the active species on both catalysts. However, the Pt to PtO2 ratio was larger on SBA-15 than on MCM-41. The in situ IR spectra suggested that the de-NOx reaction in Pt impregnated in both catalysts progressed by partial oxidation, resulting in the production of NO2, ONO, and NCO as intermediates but the de-NOx reaction was more active on Pt/SBA-15 than on Pt/MCM-41.