Active vanadium(iv) species synthesized at low-temperature facilitate excellent performance in low-temperature NOx-catalytic removal

Abstract

Vanadium-based catalysts have been extensively used to catalyze various reactions, for example, their long-term application in the de-NO_x process. Various vanadium species dispersed on carriers with a large surface area act as catalytic active sites. However, the role of crystal V₂O₅ in the selective catalytic reduction of NO_x by NH₃ remains unclear. In this study, a series of bulk vanadium oxide catalysts were synthesized by varying the synthesis temperature, among which the catalyst with a large amount of crystalline V₂O₅ synthesized at low temperatures exhibited excellent NH₃-selective catalytic reduction (NH₃-SCR) activity at low temperatures. It was found for the first time that V⁴⁺ species in this catalyst play an important role in low-temperature NH₃-SCR, which significantly improved the catalytic performance at low temperatures. The difference in the NH₃ activation of V₂O₅ with different ratios of V⁴⁺/V⁵⁺ was investigated by NH₃ temperature-programmed desorption (TPD) and in situ diffuse reflectance Fourier transform infra-red (IR-DRIFT) tests. The difference in O₂ activation was studied by O₂-TPD and ¹⁸O₂ isotope exchange experiments. The results show that a higher proportion of V⁴⁺ is more conducive to NH₃ and O₂ activation. This discovery provides a basic understanding of chemical reactions catalyzed by metal oxides and is of great significance for the development and commercial application of NH₃-SCR catalysts.