| According to statistics, there are thousands of glass kilns and ceramic kilns in our country, most of the kiln flue gas has the characteristics of high concentration of fly ash, high content of nitrogen oxides and sulfur dioxide(from 100 to 700 mg/m3), and low gas temperature(150?300?). The traditional commercial SCR denitration catalyst is not appropriate for the needs of the industrial because of its low-temperature activity and poor resistance to sulfur. Novel catalysts have a certain low temperature activity, but its poor selectivity and not resistance to sulfur which restricte its application.Thus, in this paper, we prepared of a series of catalyst making by citric acid to screen catalyst with good sulfur tolerances and selectivity for the mid-low temperature. And using the surface area analyer (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed adsorption technique (TPD/TPR), in situ DRIFTS, to study the sulfur-resistant mechanism and the mechanism of selectity for catalyst, and we made the following conclusions:(1) Experimental result showed that Cr-Ce-Co(35:60:5)(500)2h(that means the mass ratio of Cr:Ce:Co is 35:60:5,500 represents the calcination temperature is 500?,2h represents the calcination time is 2 hours)prepared by citric acid method have the best activity. When the temperature range from 180? to 280?, over 95% NO conversion and over 80% N2 selectivity were obtained with a gas hourly space velocity of 36000 h-1, after continuous operation under the conditions of 240? for 510 minutes the activity of the catalyst is still about 90%, regenerated the catalyst by high-temperature, its activity recover to its original level.(2) Using XRD?TPR?TPD?BET?in situ DRIFTS and other characterization techniques, the results showed this is only Lewis acid sites on the catalyst surface, the reaction follows the Eley-Rideal mechanism. The addition of Co decease the oxidation of catalyst, thereby it prevent the oxidation of-NH2 to-NH and N, which improve the selectivity of the catalyst.(3) The catalyst has a complete electronic cycle of itself, the different element plays a different role in the catalytic reduction reaction, Ce element in the catalytic reaction mainly plays the role of electron transfer and activation of NH3, Cr is the active center of the catalytic reaction, Co keep the reaction toward good selectivity, therefore the catalyst have sustained activity.(4) To investigate the SO2 tolerance of the catalysts, we find that SO2 destroy the Lewis acid sites on the surface, weakened the adsorption of NH3 on the catalyst surface, but at the same time it creates new Bronsted acid sites and due to the strong acidic of SO2 also increased adsorption of NH3.(5) The XRD results showed that a novel crystal phase of CoCr2O4, XPS studies showed that the presence of CoCr2O4 crystal prevent the Cr6+ poisoned by SO2, therefor the catalyst has good activity and resistance of SO2. The presence of SO2 destroyed the Ce4+ electronic circulation while it also caused more Ce3+ and more oxygen vacancies, which increase the electron flow on the catalyst surface, Therefore, the redox reactions on catalyst surface can be continued. |
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