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

Single phase perovskites, such as LaCoO3 and La1−xSrxCoO3, exhibit catalytic activity only in oxidation reactions. However, a mixture of La1−xSrxCoO3, SrCoOx and Co3O4 oxides presents both oxidation and reduction properties in the DeNOx reaction. To improve DeNOx 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=La1−xSrxCoO3+Co3O4+SrCoOx 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 C3H6-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 DeNOx activity, while the silver doping leads to a remarkable increase in the NOx-conversion from 29.4% (in the absence of Ag) to 82.4% at low temperature 220 °C in the lean burn condition.