Generation of NH 3 Selective Catalytic Reduction Active Catalysts from Decomposition of Supported FeVO 4

The effect of catalyst loading, composition, and calcination temperature on NH 3 selective catalytic reduction (SCR) activity was investigated for metal vanadates of the type Fe x Al 1–x VO 4 (0 ≤ x ≤ 1, MeVO 4 ) supported on TiO 2 –WO 3 –SiO 2 (TWS). The optimized catalyst (4.5 wt % FeVO 4 /TWS calcined at 650 °C) showed an enhanced NO x reduction activity compared to the reference material 2.3 wt % V 2 O 5 /TWS. An activation effect was observed above a calcination at 600 °C and was investigated by means of X-ray diffraction, Brunauer–Emmett–Teller, diffuse reflectance infrared Fourier transform, and X-ray absorption near edge structure analyses. It was shown that the activation is due to the decomposition of FeVO 4 . VO x species disperse and migrate to the support material, while the iron species sinter to Fe 2 O 3 particles. We provide strong evidence that the active species responsible for NH 3 –SCR in a FeVO 4 /TWS catalyst is not FeVO 4 but VO x species that possess a similar coordination environment to the VO x species on conventional V-based catalysts. Due to the remarkable effect of the activation upon calcination, a very active and thermally stable SCR catalyst up to 700 °C was obtained.