Study On CeO₂-loaded Heteropolyacid For Selective Catalytic Reduction Of NO With NH₃

NOx is one of the main air pollutants in China where selective catalytic reduction (SCR) has been considered as one of the most effective routes for stationary sourced NOx removal. Commercialized SCR catalysts (e.g. WO3-V2O5/T1O2and MoO3-V2O5/TiO2) are designed to be operated under a high operation temperature range (generally at350-450℃). This leads them have to be located between air preheater and fuel economizer, hence increasing extra equipment retrofit. Meanwhile, the flue gas temperature for lots of industrial boilers and furnaces was lower than the temperature window of commercialized SCR catalysts. As such, highly active SCR catalysts that could be operated at low temperature have recently attracted tremendous attentions.Here, we used a facile dry-mixing route for the syntheses of a series of phosphotungstic acid supported ceria (CeO2/HPW) SCR catalysts. Owe to the synergistic effect of the strong acid of HPW and the excellent redox property of CeO2, the developed CeO2/HPW catalysts had revealed remarkable SCR catalytic performance in the temperature range below300℃.In this paper, we firstly investigated the effect of CeO2loading amounts on the SCR performance of the CeO2/HPW catalysts. Experimental results revealed that the catalyst with CeO2loading of mass fraction at50%possessed the highest SCR activity, where more than90%NO conversion could be achieved in the temperature range of230-300℃for this catalyst. Moreover, high temperature calcinations at300℃and350℃on the50%CeO2/HPW catalyst would further bring an obvious enhancement in SCR acitivity, revealing more than90%NO conversion at the temperature of ca.200℃.Then, we investigated the SCR reaction mechanism of the50%CeO2/HPW catalyst by means of in situ FTIR technique. Experimental results revealed that the NO has formed NO2and nitrite intermediates over the catalyst surface during the SCR reaction, where the former had greatly increased the SCR reaction rate, hence yielding remarkable low temperature SCR activity for the catalyst. It was also found that the NH3was adsorbed on both Lewis and Br(?)nsted sites of the50%CeO2/HPW catalyst, both of which had participated into the SCR reaction.Finally, we investigated the thermal stability and potassium and sulfur poisoning resistances of the50%CeO2/HPW catalyst. Experimental results revealed that the catalyst had satisfying thermal stability where it could retain100%NO conversion within the testing at300℃for168h. After subjected to K and SO2poisoning resistance measurements, it was found that the50%CeO2/HPW catalyst had excellent anti alkali-metal poisoning ability but with relatively poor SO2poisoning resistance, which hence needs further improvements.