Monolayer Perovskite Nanosheets as a Support of Platinum for Selective Catalytic Reduction of NO _x with H ₂

Selective catalytic reduction with H 2 (H 2 -SCR) is one of the most promising techniques to suppress NO x emission from hydrogen combustion engines under lean-burn conditions. Various Na 0.5 La 0.5 B 2 O 7 -type perovskite nanosheets ( B 2 = Ta 2, NbTa, Ti 0.1 Nb 0.9 Ta 0.9 W 0.1, Ti 0.2 Nb 0.8 Ta 0.8 W 0.2, and Ti 0.3 Nb 0.7 Ta 0.7 W 0.3; thickness: 1.3–1.5 nm) derived from Aurivillius-phase layered perovskites were prepared as support materials for Pt for selective catalytic NO x reduction under NO–H 2 –O 2 conditions. The 0.3 wt % Pt/Na 0.5 La 0.5 Ti 0.2 Nb 0.8 Ta 0.8 W 0.2 O 7 2– nanosheet showed the highest H 2 -SCR activity: 82% NO conversion and 76% N 2 selectivity at 150 °C. Although the Pt-loaded non-nanosheet perovskite supports─specifically, 0.3 wt % Pt/NaTaO 3 and Na 0.5 Ca 0.5 Ti 0.5 Nb 0.25 Ta 0.25 O 3 ─showed 60–76% NO conversion, severe N 2 O generation occurred at 150–250 °C (27–39% N 2 selectivity). An in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) study revealed that the NO conversion on Pt/Na 0.5 La 0.5 NbTaO 7 2– nanosheets proceeded via the NO oxidation mechanism. Monodentate, chelating bidentate, and bridging bidentate nitrate species were detected on Pt/Na 0.5 La 0.5 NbTaO 7 2– nanosheets, whereas only chelating bidentate nitrate was detected on Pt/NaTaO 3 . The time course of the DRIFTS spectra indicated that the bridging bidentate nitrate was the most active intermediate on Pt/Na 0.5 La 0.5 NbTaO 7 2– nanosheets, whereas chelating bidentate nitrate was inactive.