Discovering the remarkable deNOx activity and anti-K poisoning of MnFeOx/H-Beta composite catalyst

Abstract

The practical application of MnFeOx catalyst is limited due to its narrow temperature window and poor resistance to alkali metal poisoning, such as K and Na. Alkali metal poisoning has always been a major factor in the deactivation of fixed-source denitration (deNOx) catalysts. Despite high activity at around 200 °C , the catalyst's susceptibility to alkali metal poisoning hinders its effectiveness. In this study, a novel MnFeOx/H-Beta composite catalyst was prepared by the simple wet impregnation method. Beta zeolite, known for its large specific surface area compared to MnFeOx, special twelve-membered ring channel, and abundant acid sites, was introduced to adjust the acid and redox active sites. This resulted in MnFeOx/H-Beta having a wider temperature window and excellent resistance to K poisoning. Notably, the NOx conversion rate exceeded 80% between 180 and 460 °C . K poisoning significantly reduces the acidity of the catalyst, as confirmed by various characterizations such as NH3-TPD and NH3 adsorption in situ DRIFTs. After K poisoning, the total acid content of MnFeOx/H-Beta decreased from 14.99 to 9.47 mmol g−1. The low acid content of MnFeOx allows the active sites to be easily covered by K, resulting in a reduction of the SCR performance, which can be attributed to the reduction of active nitrate species. The abundant acid sites of MnFeOx/H-Beta act as sacrificial sites and can coordinate with alkali metal K, thereby alleviating the poisoning of the catalyst to some extent. DFT calculations confirmed K binding to Brønsted acid sites on H-Beta zeolite, mitigating the detrimental impact of K on catalyst activity and lifetime. This research offers a pathway for designing efficient and alkali metal-resistant deNOx catalysts for real-world industrial applications.