Shape dependence of support for NOx storage and reduction catalysts

Pt/BaO/Al 2 O 3 catalysts with different BaO loadings prepared from Al 2 O 3 nanorods (Pt/BaO/Al 2 O 3 -nr) and irregular Al 2 O 3 nanoparticles (Pt/BaO/Al 2 O 3 -np) were investigated for NO x storage and reduction (NSR). The Pt/BaO/Al 2 O 3 materials derived from Al 2 O 3 nanorods always exhibited much higher NO x storage capacity (NSC) over the whole temperature range of 100–400°C than the corresponding Pt/BaO/Al 2 O 3 -np samples containing the same BaO loading, giving the maximum NSC value of 966.9 μmol/g cat at 400°C, 1.4 times higher than that of Pt/BaO/Al 2 O 3 -np. Higher catalytic performance of nanorod-supported NSR samples was also observed during lean-rich cyclic conditions (90 sec vs. 5 sec), giving more than 98% NO x conversion at 300–450°C over the Pt/BaO/Al 2 O 3 -nr sample with 15% BaO loading. To reveal this dependence on the shape of the support during the NSR process, a series of characterization techniques including the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H 2 temperature programmed reduction (H 2 -TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were also conducted. It was found that intimate contact of Ba–Al and Ba–Pt sites was achieved over the Pt/BaO/Al 2 O 3 surface when using Al 2 O 3 -nr as a support. This strong interaction among the multi-components of Pt/BaO/Al 2 O 3 -nr thus triggered the formation of surface nitrite and nitrate during the lean period, and also accelerated the reverse spillover of ad-NO x species onto the Pt surface, enhancing their reduction and leading to high NSR performance.