Revealing the deactivation mechanism of Ca poisoning on V-W-Ti catalysts in cement kilns

Abstract

Currently, Ca poisoning of the SCR catalyst was the main cause of deactivation in cement kilns. The mechanism of calcium poisoning is rarely studied. In this paper, a series of Ca poisoned V2O5-WO3/TiO2 catalysts were simulated and studied in detailed. As the NH3-SCR results showed, the NO conversion of Fresh VWT was 97.6 % at 280 °C, and decreased to 65 % when 5 % CaO was added. As the CaO content continued to increase, the NO conversion of the catalysts decreased gradually and the catalysts showed worse H2O and SO2 resistance. For a detailed understanding of the poisoning mechanism, the fresh and poisoning VWT were analyzed by using XRD, Raman, XPS, H2-TPR, NH3-TPD and in-situ DRIFTs. It was discovered that CaO not only reacted with SO2 to form CaSO4, which blocked the partial active sites, but also destroyed the dispersion of WO3 and formed CaWO4. The presence of CaWO4 could reduce the amount of medium strong and strong acids, thus inhibiting the SCR process. In-situ DRIFTs experiments showed that less nitrate intermediates were produced on 5 % CaO VWT, making it difficult to perform “fast SCR” reaction.