Effect of Potassium on the Performance of a CuSO4/TiO2 Catalyst Used in the Selective Catalytic Reduction of NOx by NH3

Owing to its renewability, abundance, and low environmental impact, biomass is considered to be a viable eco-friendly fuel. Various biofuel-fired power plants have been built worldwide to reduce carbon emissions. Potassium (K) is a typical impurity in the flue gas from biofuel combustion that can deactivate the catalyst used in the selective catalytic reduction of NOx by ammonia (NH3-SCR). CuSO4/TiO2, with excellent sulfur dioxide tolerance, is thought to be a promising vanadium-free catalyst for NH3-SCR; however, the influence of K on the CuSO4/TiO2 catalyst is still unknown. Therefore, in this study, the effect of K on the NH3-SCR performance of CuSO4/TiO2 were investigated and compared with the effect on the performance of the commercial V2O5-WO3/TiO2 (VWTi) catalyst. K-poisoned catalysts were prepared via wet impregnation using potassium acetate as the K source. Nitrogen (N2) adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3-temperature programmed desorption (NH3-TPD), H2-temperature programmed reduction (H2-TPR), and in situ diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) were used to characterize the prepared catalysts. The NOx conversion over CuSO4/TiO2 with 1.0% (w) K was 92.1% (at 350 degrees C), which was higher than the conversion (75.1%) achieved over the commercial VWTi catalyst with the same K content. The XRD, XPS, and H2-TPR results suggested that K reacted with the CuSO4 in the CuSO4/TiO2 catalyst to form CuO and K2SO4. The presence of CuO enhanced the oxidation of NH3 to N2O, NO, and NO2 during NH3-SCR, thereby decreasing the NOx conversion and N2 selectivity over CuSO4/TiO2. Moreover, based on the results from NH3-TPD and in situ DRIFTS of NH3 adsorption, it can be concluded that the Bronsted acid sites (S-OH) were poisoned by K, which restrained the adsorption of NH3 on CuSO4/TiO2. Additionally, the high K content altered the pore structure of the catalyst, leading to a decrease in the specific surface area. However, according to the in situ DRIFTS results, NH3-SCR over K-poisoned CuSO4/TiO2 still followed the Eley-Rideal mechanism: First, NH3 was adsorbed on the Lewis and Bronsted acid sites of the catalyst, and then gaseous NO and O2 reacted with the adsorbed NH3/NHa on the acid sites, resulting in the formation of N2 and H2O. Notably, the abundance of acid sites and surface-adsorbed oxygen species on CuSO4/TiO2 could be the main reason for its higher resistance to K-poisoning. In conclusion, our current findings suggested that CuSO4/TiO2 might be a suitable NH3-SCR catalyst for use in the flue gas streams from biofuel-fired power plants.