Characterization and activity of V2O5-CeO2/TiO2-ZrO2 catalysts for NH3-selective catalytic reduction of NOx

Abstract

A series of V2O5-xCeO2/TiO2-ZrO2 (Ti-Zr) catalysts with different CeO2 loadings (x = molar ratio of Ce/Ti-Zr) were prepared, and their catalytic performance for the selective catalytic reduction (SCR) of NOx by NH3 was investigated in the presence of SO2 and H2O. The physicochemical properties of the catalysts were characterized by N2 sorption analysis, high-resolution transmission electron microscopy, X-ray diffraction, H2-temperature-programmed reduction, NH3-temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The presence of CeO2 in the catalysts led to higher conversion of NOx within a wider operating temperature range. V2O5-xCeO2/Ti-Zr catalyst (x = 0.2) exhibited the highest activity. Higher loadings of CeO2 adversely affected the NOx conversion at higher temperatures. The characterization results revealed that CeO2 was amorphous and highly dispersed over the Ti-Zr support. The catalysts featured single-crystal electron diffraction features. The presence of CeO2 significantly increased the reduction ability of the catalysts, and low V2O5 loadings were beneficial to the low-temperature SCR. V2O5/TiO2 catalyst exhibited medium-to-strong and strong acid desorption of NH3, whereas V2O5/Ti-Zr featured weak acid sites onto which desorption of NH3 occurred. The presence of CeO2 could increase the amount of both the Brönsted and Lewis acid sites, which were expected to play a key role in the excellent SCR activity. In contrast, the presence of V2O5 reduced the amount of Brönsted acid sites. All V2O5-CeO2/Ti-Zr catalysts exhibited poor stability and weak resistance to H2O poisoning but high resistance to SO2. However, the original catalytic activity of V2O5-xCeO2/Ti-Zr (x = 0.3) could be fully restored following poisoning with SO2 and H2O. For the poisoned catalysts, the formation of Ce(SO4)2 led to the decreased catalytic performance at the intermediate temperatures, which increased at the higher temperatures because of the presence of V2O5.