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Nox storage and reduction over CE-ZR mixed oxide supported catalysts

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2009
Çağlar, Başar
NOx storage and reduction activities of Pt/BaO/CexZr1-xO2 (x= 1, 0.75, 0.5, 0.25, 0) catalysts were investigated by transient reaction analysis and Diffuse Reflectance Infrared Fourier Tramsform Spectroscopy (DRIFTS). Pt/BaO/Al2O3 catalyst was used as reference catalyst. Ce-Zr mixed oxides were synthesized by means of Pechini Method. Pechini method is a sol-gel like method based on mixing the related mixed oxide precursors with an α-hydroxy carboxylic acid. 10% BaO (w/w) and 1% Pt (w/w) were deposited on synthesized mixed oxide and reference alumina support via incipient wetness impregnation. Prepared catalysts were characterized by BET, XRD and in-situ DRIFTS. Pt/BaO/CexZr1-xO2 catalysts (x= 0.75, 0.5, 0.25) exhibited higher surface than pure ceria and zirconia supported catalysts and highest surface was observed for Pt/BaO/Ce0.5Zr0.5O2. The reducibility of catalysts was tested by Temperature Programmed Reduction (TPR). It was observed that the reducibility of Pt/BaO/CexZr1-xO2 catalysts increases with incorporation of Zr into ceria lattice. Pt/BaO/Ce0.25Zr0.75O2 showed the highest reducibility. The Pt dispersions of catalysts were determined by CO chemisorption. The highest Pt disperison was observed in the presence of Pt/BaO/Ce0.5Zr0.5O2 catalyst. NOx storage and reduction efficiency of the catalysts were determined by transient reaction analysis in a home-built setup at 350oC. The reaction results revealed that all catalysts exhibit similar NOX storage and reduction performance. The NOX storage performances of all catalysts were differentiated via in-situ DRIFTS analysis. Pt/BaO/CexZr1-xO2 (x= 0.75, 0.5, 0.25) catalysts revealed higher performance than the ceria and zirconia supported catalysts. Pt/BaO/Ce0.5Zr0.5O2 catalyst absorbed highest amount of NO on the surface in the form of nitrate. The reduction behaviours of catalysts also were investigated by in-situ DRIFTS. It was observed that nitrates and nitrites were completely removed from the surface after reduction by H2 at 300oC.