Thermal stability and catalytic activity of flame-made silica–vanadia–tungsten oxide–titania

Vanadia (0.9 or 2 wt.%) and silica (0–5 wt.%) doping of flame-made tungsten oxide–titania nanostructured catalyst powders (anatase, 100 m2/g, 10 wt.% WO3) is investigated. The effect of dopants on structural and chemical properties of these powders were analyzed by nitrogen adsorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and Raman spectroscopy. After calcination for 20 h at 700 °C in air, the thermally most stable composite powder conserved its specific surface area (SSA) to 90 m2/g and its anatase content to 96 wt.%. Tungsten oxide and vanadia form thin polymeric layers (∼1 nm) on the surface of the titania support. Adding silica improves the thermal and crystal stability of the catalysts even at higher reactor temperatures. As a result both NO conversion and the rate of selective catalytic reduction (SCR) with NH3 were increased.