Investigation of the selective catalytic reduction of NO with NH3 over the WO3/Ce0.68Zr0.32O2 catalyst: the role of H2O in SO2 inhibition

The effect of H2O and SO2 on the selective catalytic reduction of NOx by NH3 (NH3-SCR) over WO3/Ce0.68Zr0.32O2 at 250 degrees C was systematically investigated using various characterization techniques. NH3-SCR activity revealed that H2O in the reaction gas had little impact on the NOx conversion at 250 degrees C, whereas, the presence of SO2 slowly decreased the NOx conversion from 99.6% to 85.0% in 40 h. Particularly, the NOx conversion linearly declined to 75% with the co-existence of SO2 and H2O in 16 h. Thus, the presence of H2O obviously accelerated the deactivation of WO3/Ce0.68Zr0.32O2 compared with only the presence of SO2 under NH3-SCR conditions. Nevertheless, the above deactivation resulting from SO2 and H2O could be mostly eliminated by thermal treatment. The characterization via XRD, NO/CO2-TPD, XPS, H-2-TPR, OSC and ex/in situ DRIFT demonstrated that (NH4)(2)SO4 and Ce-2(SO4)(3) were deposited on the surface of the sulfated catalysts, which decreased the number of active sites and weakened the redox properties of WO3/Ce0.68Zr0.32O2; thus, resulting in the deactivation of the WO3/Ce0.68Zr0.32O2 catalyst. Importantly, the presence of H2O accelerated the generation of sulfates on the surface of WO3/Ce0.68Zr0.32O2, which led to the serious deactivation of the catalyst in the presence of both H2O and SO2. As a result, the Langmuir-Hinshelwood route of NH3-SCR over the catalyst was disrupted due to the shielding of sulfate species.