NH₃-SCR of NO with novel active, supported vanadium-containing Keggin-type heteropolyacid catalysts

Supported vanadium-substituted Keggin polyoxometalates (POMs) were applied as catalysts for the selective catalytic reduction of NO using NH3 as reductant (NH3-SCR). Interestingly, HPA-3 (H6PV3Mo9O40) was found to be the most active catalytic species, and TiO2 (anatase) the most promoting support for the SCR reaction in the temperature range 200-350 C. Moreover, 10 wt.% HPA 3 loading was found to be optimum resulting in nearly complete NO conversion at 350 °C. Characterization by several techniques, including N2-physisorption, NH3-TPD, FTIR, XPS and TEM showed distinctive structural HPA-3 support interactions explaining the beneficial interplay between both parts for the SCR reaction. Furthermore, different catalytically active surface species were identified at various reaction temperatures and SCR conditions by in-situ EPR spectroscopy. The study introduces a novel type of heterogeneous supported vanadium-based NH3-SCR catalysts comprising redox-active POMs, which so far mainly have been applied for homogeneously catalyzed reactions.