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

Abstract

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.