Vanadium-bearing steel slag catalysts for the selective catalytic reduction of NOx by NH3

Abstract

Selective catalytic reduction technology is the most commonly used method for NO_x control, but the preparation process of the catalysts is complicated and the preparation cost is high. In this study, a novel low-cost catalyst for selective catalytic reduction of nitrogen oxides was prepared by treating vanadium-bearing steel slag with calcination modification and sulfuric acid modification. The activity test results show that the calcination modification can slightly improve the high-temperature activity of the catalysts. Among acid-modified catalysts, sulfuric acid modification can greatly improve the denitration activity of the catalyst, and calcination of the catalyst before sulfuric acid modification can obtain a higher activity denitration catalyst. The NO_x removal efficiency of the VSS-C-S catalyst reached 82.4% at 250 °C. In addition, the catalyst modified with sulfuric acid after calcination has better water and sulfur resistance and regeneration performance. In the case of high water vapor and sulfur dioxide concentration, its denitration efficiency is 62.5%. The characterization results show that both calcination modification and sulfuric acid modification can promote the formation of α-Fe₂O₃, but calcination modification reduces the specific surface area and redox capacity of the catalysts. The sulfuric acid modification can form a new pore structure and a large number of sulfate species on the catalyst surface, and improve the existing state of vanadium species in the catalysts. The specific surface area of the VSS-C-S catalyst is 43.90 m² g⁻¹. Meanwhile, the adsorbed oxygen content of the VSS-C-S catalyst is 24% higher than that of the VSS-S-5 catalyst. It shows that the modification effect of sulfuric acid can be better exerted by calcination first and then modification with sulfuric acid. The results of in situ DRIFTS experiments show that the NH₃-SCR reaction of the calcined modified catalyst mainly follows the L–H mechanism. The NH₃-SCR reaction of sulfuric acid-modified catalysts mainly follows the E–R mechanism. The active sites on the VSS-C-S catalyst surface adsorb a large amount of NH₃ species and activate them as NH₂ active intermediates, which directly react with gaseous NO. Therefore, the catalyst modified with sulfuric acid after calcination has higher activity. The work provides a novel idea for reducing catalysts cost and promoting cleaner production.