MnO_x负载量对MnO_x/Ce_(0.7)Zr_(0.2)La_(0.1)O_2-Al_2O_3催化剂上碳烟燃烧性能的影响

Influence of MnO_x Loading on Activity of MnO_x/Ce_(0.7)Zr_(0.2)La_(0.1)O_2-Al_2O_3 Catalyst for Catalytic Combustion of Diesel Soot

采用等体积浸渍法制备了一系列不同MnOx含量的MnOx/Ce0.7Zr0.2La0.1O2-Al2O3(Ce0.7Zr0.2La0.1O2/Al2O3质量比=1)催化剂,并用X射线衍射、低温N2吸附-脱附、X射线光电子能谱、O2程序升温脱附和H2程序升温还原等手段对催化剂进行了表征,考察了催化剂催化柴油车排放碳烟颗粒物燃烧的反应性能.结果表明,催化剂表面吸附的活性氧物种和MnOx的低温区还原性能是决定催化剂活性的两大关键因素.当MnOx负载量为5%时,催化反应所需的活性氧减少,因而活性降低;但MnOx负载量增至10%时,催化剂中Mn物种的可还原量提高,从而增加其活性;增至20%时,MnOx与表面吸附氧物种的可还原量间达平衡最佳值,活性最佳,碳烟起燃温度比无催化剂时降低了179oC;负载量达30%后,由于载体表面吸附氧物种数量的降低和还原峰温的上升使催化剂活性下降.

A series of MnOx/Ce0.7Zr0.2La0.1O2-Al2O3 supported catalysts with the Ce0.7Zr0.2La0.1O2：Al2O3 mass ratio of 1：1 and different MnOx loadings were prepared by the incipient wetness method. The catalysts were characterized by X-ray diffraction, low temperature N2 adsorption-desorption, X-ray photoelectron spectroscopy, O2 temperature-programmed desorption, and H2 temperature-programmed reduction. The catalytic performance of these catalysts for the combustion of diesel soot was investigated. It is found that surface-adsorbed active oxygen species and low-temperature reducibility of MnOx are the determinants of catalytic activity. When the MnOx loading is 5%, the catalyst activity decreases owing to the loss of active oxygen species, which are necessary for the catalytic combustion. When the MnOx loading is in- creased to 10%, the catalyst activity is dramatically increased because of the enhanced reducible manganese species. Interestingly, the optimal values for reducible manganese species and surface-adsorbed oxygen species can be achieved in the catalyst with 20% MnOx, and so the catalyst exhibits the best catalytic activity, giving a light-off temperature about 179 oC lower than that of the non-catalytic soot combustion. With a further addition of MnOx species up to 30%, its catalytic activity is deteriorated mainly due to the decrease in surface-trapped oxygen species and upper shift of the reduction temperature.