Monolayer Perovskite Nanosheets as a Support of Platinum for Selective Catalytic Reduction of NO _<i>x</i> with H ₂

Selective catalytic reduction with H2 (H2-SCR) is one of the most promising techniques to suppress NOx emission from hydrogen combustion engines under lean-burn conditions. Various Na0.5La0.5B2O7-type perovskite nanosheets (B2 = Ta2, NbTa, Ti0.1Nb0.9Ta0.9W0.1, Ti0.2Nb0.8Ta0.8W0.2, and Ti0.3Nb0.7Ta0.7W0.3; thickness: 1.3–1.5 nm) derived from Aurivillius-phase layered perovskites were prepared as support materials for Pt for selective catalytic NOx reduction under NO–H2–O2 conditions. The 0.3 wt % Pt/Na0.5La0.5Ti0.2Nb0.8Ta0.8W0.2O72– nanosheet showed the highest H2-SCR activity: 82% NO conversion and 76% N2 selectivity at 150 °C. Although the Pt-loaded non-nanosheet perovskite supports─specifically, 0.3 wt % Pt/NaTaO3 and Na0.5Ca0.5Ti0.5Nb0.25Ta0.25O3─showed 60–76% NO conversion, severe N2O generation occurred at 150–250 °C (27–39% N2 selectivity). An in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) study revealed that the NO conversion on Pt/Na0.5La0.5NbTaO72– nanosheets proceeded via the NO oxidation mechanism. Monodentate, chelating bidentate, and bridging bidentate nitrate species were detected on Pt/Na0.5La0.5NbTaO72– nanosheets, whereas only chelating bidentate nitrate was detected on Pt/NaTaO3. The time course of the DRIFTS spectra indicated that the bridging bidentate nitrate was the most active intermediate on Pt/Na0.5La0.5NbTaO72– nanosheets, whereas chelating bidentate nitrate was inactive.