Lanthanum-promoted copper-based hydrotalcites derived mixed oxides for NO_x adsorption, soot combustion and simultaneous NO_x-soot removal

摘要

La-promoted Cu-based hydrotalcites derived mixed oxides were prepared and their catalytic activities for NO_x adsorption, soot oxidation, and simultaneous NO_x-soot removal were investigated. The catalysts were characterized by XRD, DTG, BET, FTIR, H2-TPR, TPD and TPO techniques. The oxides catalysts exhibited mesoporous properties with specific surface area of 45-160 m~2/g. The incorporation of La and Cu decreased the amount of basic sites due to the large decrease in surface areas. Under O_2 atmosphere, La incorporation is dominant for soot oxidation activity, while Cu favors high selectivity to CO_2 formation. A synergetic effect between La and Cu for catalyzed soot oxidation lies in the improved redox property and suitable basicity. The presence of NO in O_2 significantly promoted soot oxidation on the catalysts with the ignition temperature decreased to about 300 C. In O_2/NO atmosphere, NO_2 acts as an intermediate which oxidizes soot to CO_2 at a lower temperature with itself reduced to NO or N_2, contributing to the high catalytic performance in simultaneous removal of NO_x, and soot.