Deactivation\nMechanism of Multipoisons in Cement Furnace\nFlue Gas on Selective Catalytic Reduction Catalysts

Abstract

Increasing numbers of cement furnaces\nhave applied selective catalytic\nreduction (SCR) units for advanced treatment of NO in the flue gas.\nHowever, the SCR catalysts may face various poisons, such as acidic,\nalkaline, and heavy metal species, in the fly ash. In this work, we\nstudied the deactivation mechanisms of multipoisons (Ca, Pb, and S)\non the CeO₂–WO₃/TiO₂ catalyst,\nusing the <i>in situ</i> diffuse reflectance infrared Fourier\ntransform spectroscopy method. Calcium promoted the conversion of\nCe­(III) to Ce­(IV) and, thus, (i) suppressed the redox cycle, (ii)\ndecreased the NO adsorption (monodentate NO₃^– and bridged NO₂^–), and (iii) enriched\nthe Lewis acid sites. Pb­(IV) blocked Ce₂(WO₄)₃, aggravating the electronegativity of W⁶⁺, which inhibited (i) the binding stability of tungsten and ammonia\nspecies, (ii) bridged NO₃^– (bonded to\ntungsten), and (iii) the Brønsted acid sites. The multipoisoning\nprocesses enriched O^2– by repairing partial surface\noxygen defects, which suppressed O₂^2– and O^–. Sulfur occupied the surface base sites\nand formed PbSO₄ after Ce₂(WO₄)₃ was saturated.