Effect of Potassium on the Performance of a CuSO₄/TiO₂ Catalyst Used in the Selective Catalytic Reduction of NO_<i>x</i> by NH₃

Abstract

Owing to its renewability, abundance, and low environmental impact, biomass is considered to be a viable eco-friendly fuel. Various biofuelfired 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), H2temperature 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 °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 Brønsted 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 Brønsted acid sites of the catalyst, and then gaseous NO and O2 reacted with the adsorbed NH3/NH4+ 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.

Formaldehyde Ambient-Temperature Decomposition over Pd/Mn3O4–MnO Driven by Active Sites’ Self-Tandem Catalysis

“…The oxidation of HCHO typically involves overcoming the energy barrier of two major rate-determining steps: the formation of formate species (HCHO → HCOO – ) and their subsequent decomposition (HCOO – → H 2 CO 3 → CO 2 ). − Considerable efforts have been devoted to addressing both steps simultaneously, through the enhancement of oxygen activation, − regulation of oxygen vacancy − and metal–support interaction, − as well as other related strategies. − However, a more profound understanding is still imperative for the rational design of HCHO oxidation catalysts with enhanced intrinsic activity and reduced noble metal loading. Intrinsically, different materials exhibit varying catalytic abilities for each reaction step.…”