Catalytic deNO x properties of novel vanadium oxide based open-framework materials

The deNOx catalytic properties of a new class of open-framework structure materials, Li6[Mn3(H2O)12V18O42(XO4)] · 24H2O (X = V, S) (1), [Fe3(H2O)12 V18O42(XO4)] · 24H2O (X = V, S) (2), [Co3(H2O)12V18O42(XO4)] · 24H2O (X = V, S) (3), and Li6[Ni3II(H2O)12V16VIV2VO42(SO4)] · 24H2O (4), have been studied. The crystal structures of these novel systems consist of three-dimensional arrays of vanadium oxide clusters {V18O42(XO4)} , as building block units, interlinked by {–O–M–O–} (M = Mn, 1; M = Fe, 2; M = Co, 3; M = Ni, 4) bridges. Their open-framework structures contain cavities, similar to those observed in conventional zeolites, which are occupied by exchangeable cations and/or readily removable water of hydration. The catalysts derived from these materials were tested for the selective catalytic reduction (SCR) of nitrogen oxides {NOx} into N2 using a hydrocarbon, propylene, as the reducing agent. The catalysts were ineffective under lean burn conditions. However, the new catalysts, especially the one derived from the cobalt derivative (3), showed intriguing deNOx activity under rich conditions. They remove up to ~ 99% of the toxic NOx emissions in 1.5% O2 with 100% selectivity to N2. The active phase of the catalysts exhibit good stability, can be readily regenerated, and are selective to the desired product-N2. The catalytic reactions occur at moderately low temperatures (400–500 °C). The catalysts were characterized by FT-IR, temperature programmed reactions (TPR and TPO), SEM, BET surface area measurements, elemental analysis, and X-ray diffraction (XRD). Additional advanced techniques were used to further characterize the catalyst phases that showed most promising deNOx activity and increased tolerance to oxygen.