Design Strategies for P-Containing Fuels Adaptable CeO_2-MoO_3 Catalysts for DeNO_x: Significance of Phosphorus Resistance and N_2 Selectivity

摘要

Phosphorus compounds from flue gas have a significant deactivation effect on selective catalytic reduction (SCR) DeNO_x catalysts. In this work, the effects of phosphorus over three catalysts (CeO_2, CeO_2-MoO_3, and V_2O_5-MoO_3/ TiO_2) for NH_3-SCR were studied, and characterizations were performed aiming at a better understanding of the behavior and poisoning mechanism of phosphorus over SCR catalysts. The CeO_2-MoO_3 catalyst showed much better catalytic behavior with respect to resistance to phosphorus and N_2 selectivity compared with V_2O_5-MoO_3/TiO_2 catalyst With addition of 1.3 wt % P, the SCR activity of V_2O_5-MoO_3/TiO_2 decreased dramatically at low temperature due to the impairment of redox property for NO oxidation; meanwhile, the activity over CeO_2 and CeO_2-MoO_3 catalysts was improved. The superior NO oxidation activity contributes to the activity over P-poisoned CeO_2 catalyst. The increased surface area and abundant acidity sites contribute to excellent activity over CeO_2-MoO_3 catalyst As the content of P increased to 3.9 wt %, the redox cycle over CeO_2 catalyst (2CeO_2 (←→) Ce_2O_3 + O~*) was destroyed as phosphate accumulated, leading to the decline of SCR activity; whereas, more than 80% NO_x, conversion and superior N_2 selectivity were obtained over CeO_2-MoO_3 at T ＞ 300 ℃. The effect of phosphorus was correlated with the redox properties of SCR catalyst for NH3 and NO oxidation. A spillover effect that phosphate transfers from Ce to Mo in calcination was proposed.