用传统的等体积浸渍法或蒸发法制备了Ni/La_2O_3/γ-Al_2O_3与Ni/La_2O_3/α-Al_2O_3催化剂,在没有稀释气体的条件下进行了甲烷干重整反应.采用H_2程序升温还原、N_2吸附脱附、X射线衍射、透射电子显微镜、热重-差示扫描热量以及程序升温加氢等手段对新鲜的与反应后的催化剂以及沉积的碳进行了表征.结果表明,催化剂上有四种含碳物种,以三种形态存在,即无定形碳(聚合态)、丝状碳或石墨碳.这些催化剂上积炭的数量与种类各不相同,依赖于催化剂中金属Ni颗粒的大小与载体的织构特性.丝状碳的形成及其形貌与金属Ni颗粒的大小有着密切的联系.Ni颗粒小于15nm时能抑制丝状碳的形成与沉积.减少积炭的数量,同时能产生较多的活性C_a物种,从而在一定程度上导致催化剂具有较好的活性与稳定性.%Ni/La_2O_3/γ-Al_2O_3 and Ni/La_2O_3/α-Al_2O_3 catalysts were prepared by the incipient wetness impregnation and evaporation methods. Their catalytic properties for the dry reforming of methane without a diluting gas were studied. The fresh and used catalysts and deposited carbon were characterized by H_2 temperature-programmed reduction, N_2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, thermogravimetry coupled to differential scanning calorimetry, and temperature-programmed hydrogenation. The results showed that there were four carbon species that existed as three types, namely, amorphous (polymeric), filamentous, and graphitic carbon. The amount and type of carbon species on the catalysts depended on the size of Ni particles and texture of the support. The formation and morphology of filamentous carbon were clearly related to the size of Ni particles. Ni particles less than 15 nm suppressed the formation and deposition of filamentous carbons, decreased the amount of carbon deposition, and had more active C_α species, resulting in a better activity and higher stability of the catalysts.
展开▼
