Insight into the Alkali Resistance Mechanism of CoMnHPMo Catalyst for NH₃ Selective Catalytic Reduction of NO

Abstract

The existence of alkali metals in flue gases originating from stationary sources can result in catalyst deactivation in the low-temperature selective catalytic reduction (SCR) of nitrogen oxides (NO _x). It is widely accepted that alkali metal poisoning causes damage to the acidic sites of catalysts. Therefore, in this study, a series of CoMn catalysts doped with heteropolyacids (HPAs) were prepared using the coprecipitation method. Among these, CoMnHPMo exhibited superior catalytic performance for SCR and over 95% NO _x conversion at 150–300 ℃. Moreover, it exhibited excellent catalytic activity and stability after alkali poisoning, demonstrating outstanding alkali metal resistance. The characterization indicated that HPMo increased the specific surface area of the catalyst, which provided abundant adsorption sites for NO _x and NH₃. Comparing catalysts before and after poisoning, CoMnHPMo enhanced its alkali metal resistance by sacrificing Brønsted acid sites to protect its Lewis acid sites. In situ DRIFTS was used to study the reaction pathways of the catalysts. The results showed that CoMnHPMo maintained high NH₃ adsorption capacity after K poisoning and then reacted rapidly with NO intermediates to ensure that the active sites were not covered. Consequently, SCR performance was ensured even after alkali metal poisoning. In summary, this research proposed a simple method for the design of an alkali-resistant NH₃-SCR catalyst with high activity at low temperatures.

Keywords

NH₃-SCR; Alkali resistance; Phosphomolybdic acid; CoMn

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