A study on the catalytic synergism between K and Pd in Co3Al(O) hydrotalcite-derived oxide catalysts used for soot combustion

The K/Co3-xPdxAl(O) (x=0 or 0.02) and K/Pd/Co3Al(O) catalysts promoted by K and Pd were synthesized by using pH constant co-precipitation and successive impregnation methods through the precursors of hydrotalcites. The physicochemical properties of these catalysts were systematically characterized by XRD, EXAFS, XANES, XPS, HRTEM, H-2-TPR, soot-TPR and in situ FT-IR. It is found that the catalyst K/Pd/Co3Al(O) prepared by successive impregnation displays the lowest characteristic temperatures including the initial and final combustion temperatures (T-i and T-f). The coexistence of K and Pd in K/Pd/Co3Al(O) or K/Co3-xPdxAl(O) can improve both the reducibility and the oxidizabilily of the catalysts, generating a prominent catalytic synergism on soot oxidation. K-Co-O and K-Pd-O have been identified as the main active phases in the catalysts simultaneously promoted by K and Pd. Based on the results of in-situ FT-IR three potential reaction pathways for soot combustion have been revealed, namely the direct soot oxidation, nitrate enhanced soot oxidation and NO2-assisted soot oxidation. As compared with the conventional Pd/Al2O3 catalyst, the as-prepared K/Pd/Co3Al(O) catalyst possesses much higher thermal stability. (C) 2015 Elsevier Ltd. All rights reserved.