Nitrogen oxides (NOx) are one of the important root causes of smog and ozone pollution, and are important precursors of the main atmospheric pollutants PM2.5 and ozone e (Zhang et al., 2020; Yang et al., 2018). Its main sources are caused by emissions from motor vehicle exhaust, coal-fired power plants, and industrial sources (steel, coking, cement, glass, and ceramics), among which industrial source emissions are the main source of atmospheric NOx (Ashraf et al., 2019; Agbo et al., 2021; Dadi et al., 2021). In recent years, although motor vehicle exhaust and NOx emissions from coal-fired power plants have been well controlled and reduced, industrial source NOx emissions have not been effectively controlled (Ma et al., 2018).
SCR (Selective Catalytic Reduction) technology initially used a precious metal platinum catalyst to treat NOx (Zhao et al., 2020). Although it can solve practical industrial problems, the cost of the catalyst is high and a large number of by-products of ammonium nitrate will be generated in the active temperature range (Vogel et al., 2020; Li et al., 2020; Chen et al., 2014). The highly active commercial SCR catalyst developed and improved afterwards has been effectively used in industrial production. However, the flue gas temperature in the non-electric power industry is low, so the existing mature SCR denitration technology cannot fully control NOx (Zhang et al., 2021; Jaegers et al., 2019).
At present, the industrial flue gas denitration catalysts that are commercially used are mainly vanadium-titanium type, because they have higher NH3-SCR catalytic activity at 280–450℃, and the catalysts have higher toxicity and poor sulfur resistance (Theofanidis et al., 2018; Jablonska et al., 2018; Jogi et al., 2018). It is urgent to find a catalyst with low temperature activity, weak catalyst toxicity and sulfur resistance to replace the commercial vanadium titanium catalyst. The Mn-based catalyst has a wide distribution of valence states of active components, and manganese between different valence states can be converted to each other to produce redox, which can make NH3 selectively reduce NO and promote the SCR reaction (Abazari et al., 2021; Schroeder et al., 2020). However, SO2 in the flue gas will also poison the Mn-based catalyst and has not been applied in industry. When the multi-metal oxide catalyst shows more excellent low temperature activity, it also has certain sulfur resistance and longer service life (Italiano et al., 2016; Lei et al., 2020; Wang et al., 2018).
The active components dispersed on the surface of the carrier can optimize the performance of the catalyst (Wahiduzzaman et al., 2018; Tamura et al., 2018). The catalysts used in practice all have a certain shape, such as plate, honeycomb, spherical, etc. The shaped carrier will significantly improve the performance of the catalyst (Jun et al., 2020). Due to the relatively small amount of industrial flue gas in the non-power industry, the demand for plate and honeycomb catalysts is relatively small. For the demand for denitration technology and catalysts in glass furnaces, cement and other industries, the use of small catalysts can achieve energy saving and emission reduction and reduce the cost of investment (Chen et al., 2020; Faizullina et al., 2020). At present, industrially prepared denitration catalyst carriers mostly use industrially prepared oxides such as SiO2, TiO2 and Al2O3, etc., which is also an expensive investment for small enterprises (Abdelhamid et al., 2019; Chen et al., 2017). Therefore, choosing a carrier with low cost and wide source is essential to promote the full implementation of denitration technology in small industries (Han et al., 2019; Sun et al., 2018).
Lag is a by-product of the blast furnace ironmaking process. In the ironmaking process, iron oxide is reduced to metallic iron at high temperatures. Impurities such as silica and alumina in the iron ore react with lime to form a melt with silicate and aluminosilicate as the main components. After being quenched into a loose, porous granular material, it is called blast furnace slag (BFS). It is waste slag discharged during blast furnace smelting, and its output accounts for 30–50% of pig iron output. A large amount of slag is produced every year. Without proper treatment, the residual products occupy a large amount of high-quality land resources, which will not only cause environmental pollution, but also cause serious waste of resources (Rahman et al., 2019; Selvamani et al., 2017). However, because the current slag is mainly based on the preparation of cement or vitreous, it is a waste of resources for the slag to be rich in elements. With the research and understanding of the performance of slag, people began to study and use slag in multiple directions. For the cement manufacturing industry and the glass furnace industry, blast furnace slag is one of the important raw materials used, coupled with the company's demand for denitration catalysts, so this article selects solid waste blast furnace slag as the carrier of denitration catalysts (Veerapandian et al., 2019; Vita et al., 2018).
In this paper, it is proposed to prepare denitration catalyst carrier with blast furnace slag, and load another active assistant on the basis of Mn based blast furnace slag at the same time. The modification of Mn based blast furnace slag can improve the denitration performance and obtain better sulfur resistance performance at the same time. It can not only expand the use of blast furnace slag, but also meet the needs of relevant enterprises to meet the emission reduction standards, so as to achieve the purpose of combining the utilization of solid waste resources with the control of air pollution.