The Synthesis, Characterization And SCR Performance Of CuFe₂O₄ Catalyst

Nitrogen oxides (NOX) are one of the important atmospheric pollutants. The iron-based spinel and ZSM-5, SBA-15 molecular sieve supported catalyst have attracted a great deal of concern because of its high catalytic activity in the SCR reaction.In this paper, unsupported CuFe2O4 catalyst and supported Fe-CuOx/ZSM-5, CuFe2O4/SBA-15 catalysts were prepared, and the NH3-SCR performance of these catalysts was tested in a fixed-bed reactor. XRD, SEM, TEM, TPD, XPS and other characterization methods were used to characterize the structure and properties of catalysts.The experiment results showed that, catalyst prepared by PS spheres, processed by ammonium oxalate had a higher NOX conversion of 85% range from 240 to 330 than other samples mainly due to its rough surface. XRD showed that CuFe2O4 prepared by different methods had high crystallinity, diffraction peaks of Fe2O3 also can be detected. TEM micrographs indicated that the prepared samples exhibited hollow spherical structure.For Fe-CuOx/ZSM-5 catalyst, the NOx conversion over sample (Fe:Cu= 2:1) reached 98% within the temperature range from 180 to 360℃. Ultrasonic impregnation can promote active component to highly disperse into the channel of ZSM-5, thus diffraction peaks of CuFe2O4 can not be observed by XRD until the loading reached 25%. XPS results showed, catalyst contained the maximum chemisorbed oxygen when the molar ratio of iron and copper was 2:1. In situ DRIFTS results revealed that catalyst had oxidation activity against NO and NH3 under oxygen-free condition due to action of chemisorbed oxygen. XPS analysis were used to deeply study the properties of chemisorbed oxygen and its influence on SCR activities, in situ DRIFTS was used to study adsorption and reaction of NO and NH3 on the catalyst, and reaction model was obtained based on it.Fe-SBA-15 samples exhibited relatively higher NOx conversion than SBA-15, the introduction of Al results in the generation of Bronsted acid site, further improving the SCR performance, with about 100% conversion at 480℃. Both small angle XRD and TEM results indicated that all the samples exhibited well-ordered mesoporous structure. Sulfur doped CuFe2O4/Al-Fe-SBA-15 catalyst demonstrated superior resistance to SO2. IR results showed that sulfur incorporated into the catalyst will generate sulfate or bisulfate, XPS of S 2p confirmed the sulfur had two valence states of S2" and S6+.