Improvement of DeNO x catalytic activity of nanosized mixed oxides of La, Sr and Co by Ag doping

Abstract

Single phase perovskites, such as LaCoO 3 and La 1−x Sr x CoO 3, exhibit catalytic activity only in oxidation reactions. However, a mixture of La 1−x Sr x CoO 3, SrCoO x and Co 3 O 4 oxides presents both oxidation and reduction properties in the DeNO x reaction. To improve DeNO x activity, we have added 1–2 wt% of Ag to a mixture of nanosized oxides of La, Sr and Co. These mixtures (with and without Ag) were prepared by the sol–gel method using citric acid as the solvent. Two kinds of mixtures, A=La 1−x Sr x CoO 3+Co 3 O 4+SrCoO x and B=A+Ag, were characterized by x-ray diffraction (XRD) analysis, field emission scanning electron microscope (FESEM) and energy dispersive x-ray spectroscopy (EDS). Their catalytic activity was studied by temperature programmed surface reaction (TPSR). The results showed that (i) for catalyst A, the total C 3 H 6-conversion temperature is in the range 210–500 °C, while for catalyst B that is 200–400 °C; (ii) the mixed oxide A exhibits a weak DeNO x activity, while the silver doping leads to a remarkable increase in the NO x -conversion from 29.4% (in the absence of Ag) to 82.4% at low temperature 220 °C in the lean burn condition.