The effects of tungsten and hydrothermal aging in promoting NH3-SCR activity on V2O5/WO3-TiO2 catalysts
Abstract
The fresh catalysts of V2O5-TiO2 (VTi) and V2O5/WO3-TiO2 (VWTi) were prepared via an impregnation method. The hydrothermal aged samples were obtained at 750 °C for 24 h under airflow with 10 vol% water vapor. Compared to the fresh catalysts, the catalytic performance of the aged catalysts (VTi-A and VWTi-A) has been significantly improved. Particularly, VWTi-A displayed the best activity over a wide temperature range (NOx conversion: >90% @ 250-550 °C). Structural characterizations indicated that the surface area of the aged catalysts was dramatically decreased, and the morphologies of catalysts also changed. The X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), and Raman results demonstrated that hydrothermal aging greatly influenced the migration and agglomeration of vanadium species. As a result, numerous active polymeric VOx species were emerged on the surface of catalysts. More importantly, XPS results revealed that more low valence vanadium species (V4+ and V3+) was produced on the VWTi-A catalysts than that of VTi-A after hydrothermal aging. These low valence vanadium species resulted in considerably higher SCR activity than the high valence vanadium species (V5+). Consequently, both polymeric surface VOx species and low valence vanadium species determined the enhanced low-temperature SCR behavior of the aged catalysts.
- Publication:
-
Applied Surface Science
- Pub Date:
- November 2018
- DOI:
- 10.1016/j.apsusc.2018.08.046
- Bibcode:
- 2018ApSS..459..639C
- Keywords:
-
- V<SUB>2</SUB>O<SUB>5</SUB>/WO<SUB>3</SUB>-TiO<SUB>2</SUB>;
- Hydrothermal treatment;
- Polymeric surface VO<SUB>x</SUB>;
- Low valence vanadium;
- NH<SUB>3</SUB>-SCR