Effect of chromium oxide as active site over TiO2-PILC for selective catalytic oxidation of NO

This study introduced TiO₂-pillared clays (TiO₂-PILC) as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350°C, the NO conversion was 61% under conditions of GHSV = 23600 hr⁻¹. The BET data showed that the support particles had a mesoporous structure. H₂-TPR showed that Cr(10)TiP (10 wt.% Cr doping on TiO₂-PILC) clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO + O₂ adsorption, the intensity of evolution of superoxide ions (O₂⁻) increased. The content of Cr³⁺ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr³⁺ increased to 50.28%. Additionally, O_α/O_β increased markedly through the oxidation process. The NO conversion decreased when SO₂ was added into the system, but when the SO₂ was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO₄²⁻.