Deactivation Mechanism of Multipoisons in Cement Furnace Flue Gas on Selective Catalytic Reduction Catalysts

Abstract

Increasing numbers of cement furnaces have applied selective catalytic reduction (SCR) units for advanced treatment of NO in the flue gas. However, the SCR catalysts may face various poisons, such as acidic, alkaline, and heavy metal species, in the fly ash. In this work, we studied the deactivation mechanisms of multipoisons (Ca, Pb, and S) on the CeO₂-WO₃/TiO₂ catalyst, using the in situ diffuse reflectance infrared Fourier transform spectroscopy method. Calcium promoted the conversion of Ce(III) to Ce(IV) and, thus, (i) suppressed the redox cycle, (ii) decreased the NO adsorption (monodentate NO₃^- and bridged NO₂^-), and (iii) enriched the Lewis acid sites. Pb(IV) blocked Ce₂(WO₄)₃, aggravating the electronegativity of W⁶⁺, which inhibited (i) the binding stability of tungsten and ammonia species, (ii) bridged NO₃^- (bonded to tungsten), and (iii) the Brønsted acid sites. The multipoisoning processes enriched O^2- by repairing partial surface oxygen defects, which suppressed O₂^2- and O^-. Sulfur occupied the surface base sites and formed PbSO₄ after Ce₂(WO₄)₃ was saturated.