Exploration of surface properties of Sb-promoted copper vanadate catalysts for selective catalytic reduction of NO_X by NH₃

A way to fulfill efficient exploitation of desired catalytic nature provided by V oxide is to modify its chemical structure through the incorporation of secondary transition metal species. This paper reports the use of Cu as a modifier of high-valent V oxide (V₂O₅) to produce a class of copper vanadates and their utilization as active sites for the selective catalytic reduction of NO_X (X = 1 or 2) by NH₃ (NH₃-SCR). All catalysts contained ∼2 nm-sized copper vanadate particles highly dispersed on anatase with desired vanadate phases. The anatase-supported Cu₅V₂O₁₀ provided a greater quantity of acid sites with improved redox character than Cu₁V₂O₆, Cu₂V₂O₇, and Cu₃V₂O₈, thereby exhibiting the greatest NH₃-SCR performance under ideal reaction conditions. Anatase-supported Cu₃V₂O₈, however, was found to possess the most preferred surface properties among the catalysts post sulfation. This was evidenced by NH₃-SCR runs of the catalysts under reaction conditions with H₂O and SO₂-including stream, where all catalysts were pre-sulfated by SO₂ and O₂ at elevated temperatures. The NH₃-SCR performance of the optimum Cu₃V₂O₈ on anatase was further promoted after sulfation of the catalyst with the optimum content of Sb promoter. The Sb promoter was verified to enhance the redox feature and minimize the interactions among catalyst surfaces and SO₂/ammonium (bi)sulfates during the NH₃-SCR, as evidenced by durability experiments. While showing N₂ selectivities as ∼100% at ≤ 400 °C, the optimized Sb-promoted Cu₃V₂O₈ on anatase showed high NO_X conversions (≥ ∼85%) at ≥ 220 °C and outperformed the control vanadia-tungstate on anatase, which was used to simulate a commercial catalyst. This paper remarks the exploration of the variable structures of metal vanadates can be a good strategy to discover high-performance catalytic solids for the reduction of NO_X species.