The role of copper in the enhanced performance of W/Ti catalysts for low-temperature selective catalytic reduction

Abstract

The influence of copper (Cu) on the performance of a selective catalytic reduction (SCR) WOx/TiO2 catalyst was investigated. The properties of the catalysts were investigated by Brunauer-Emmett-Teller (BET) analysis, Raman spectroscopy, temperature programmed desorption (TPD), temperature programmed reduction (TPR), in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTs), and X-ray photoelectron spectroscopy (XPS). The addition of Cu led to an interaction between the octahedral WOx species in W/TiO2 catalysts, which increased the redox capacities of the catalysts, thereby enhancing the low-temperature performance of the catalysts at ≤350 °C. In contrast, the addition of Cu above certain content (~1.0 wt%) resulted in the generation of polymerized or bulk CuOx, which inhibited the enhancement of low-temperature performance. Furthermore, the increased capacity for oxidation resulted in increased rates of NH3 oxidation, which reduced the performance of the catalyst in the high-temperature region at temperatures exceeding 500 °C. The adsorption characteristics of the W-Cu/TiO2 catalyst following the addition of Cu exhibited a decrease in Brønsted-acid sites while an increase in Lewis-acid sites. Moreover, by inhibiting the production of adsorption NOx species, such as monodentate nitrate, while inducing physical adsorption of NOx, resulted in the generation of NO2(ad), thereby promoting the ‘Fast SCR’ on the catalyst.