A series of CuSO 4 /TiO 2 catalysts were prepared using a wet impregnation method. The activity of each sample in the selective catalytic reduction of NO by NH 3 (NH 3 -SCR) was determined. The effects of SO 2 and H 2 O, and their combined effect, on the activity were examined at 340 °C for 24 h. The catalysts were characterized using N 2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction of H 2 (H 2 -TPR), temperature-programmed desorption of NH 3 (NH 3 -TPD), and in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS). The CuSO 4 /TiO 2 catalysts had good activities, with low production of N 2 O above 340 °C. SO 2 or a combination of SO 2 and H 2 O had little effect on the activity, and H 2 O caused only a slight decrease in activity during the experimental period. The NH 3 -TPD and H 2 -TPR results showed that CuSO 4 increased the amounts of acid sites and adsorbed oxygen on the catalyst. In situ DRIFTS showed that the NH 3 -SCR reaction on the CuSO 4 /TiO 2 catalysts followed an Eley–Rideal mechanism. The reaction of gaseous NO with NH 3 adsorbed on Lewis acid sites to form N 2 and H 2 O could be the main reaction pathway, and oxygen adsorption might favor this process.
Yanke Yu,Desheng Wei,Zhaojian Tong,Jinxiu Wang,Jinsheng Chen,Chi He
Ammonia (NH 3 ) is a critical component causing environmental problems like haze and water pollution. Selective catalytic oxidation of ammonia (NH 3 -SCO) to N 2 and H 2 O is a promising method to abate NH 3 emission. However, inferior SO 2 tolerance is still a tremendous challenge to be conquered for present NH 3 -SCO catalysts regarding practical applications. Application of materials which was difficult to be sulfated by SO 2 should be an effective way to solve this problem. Here, a ReO x -CuSO 4 /TiO 2 catalyst which coupled the advantages of ReO x (Rhenium oxides, supplying highly active adsorbed surface oxygen enhancing NH 3 -SCO reaction) and CuSO 4 (providing Brønsted acid sites inhibiting the formation of N 2 O) was rationally fabricated. Results indicated that ReO x -CuSO 4 /TiO 2 catalyst exhibited excellent catalytic performance in NH 3 -SCO with almost 100% of NH 3 oxidized at 300 °C (N 2 selectivity as high as 96%). Crucially, the composite catalyst exhibited incredible activity and stability under harsh reaction conditions toward SO 2 (600 ppm) and H 2 O (4.0 vol%) owing to the superior inhibition capability for SO 2 adsorption. In situ DRIFTS, in situ Raman and in situ XPS demonstrated that the NH 3 -SCO reaction over ReO x -CuSO 4 /TiO 2 catalyst mainly obeyed a N 2 H 4 reaction mechanism and oxidation–reduction circle between Re 7+ and Re 6+ played a vital role. Moreover, SO 2 would not affect this reaction mechanism on ReO x -CuSO 4 /TiO 2 catalyst. The knowledge and understanding reported could provide critical insights for the design and optimization of efficient materials for industrial NH 3 oxidative elimination.
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