流化床反应器中不同Ni/Al2O3催化剂上CH4-CO2重整反应性能的比较研究

采用浸渍法、溶胶 凝胶过程与普通干燥、超临界干燥过程相结合的方法制备了三种20%的NiO-Al2O3体系催化剂，利用BET、XRD、H2 TPR、H2-TPD等方法对各催化剂样品物化性质进行了表征，并考察了催化剂在流化床反应器中CH4-CO2重整反应的催化性能。研究结果表明，经923K焙烧后气凝胶催化剂中镍与载体间作用力最强，主要为固定NiO和尖晶石NiAl2O4结构，而浸渍型催化剂和干凝胶催化剂中镍与载体间作用力较弱。三种催化剂中，气凝胶催化剂具有比表面积较大、堆密度较低、Ni还原度及分散度较高的特点。它在流化床反应器中所形成的聚团流态化状态具有较高的床层膨胀率，大量多孔疏松状的纳米颗粒聚团在床内的循环运动有效地提高了传质效率，能使得生成的沉积炭快速得到气化，从而抑制了催化剂失活；对于浸渍型催化剂和干凝胶催化剂，流化床反应器中床层膨胀率较低、颗粒循环量较少、传质效率较低，易于造成催化剂表面积炭失活。经用TG和XRD等方法对反应后催化剂分析表征，证明催化剂表面石墨碳的沉积是导致浸渍型催化剂和干凝胶催化剂失活的主要原因。

Comparative study of CH4-CO2 reforming over different Ni/Al2O3 catalysts in a fluidized bed reactor

Using incipient impregnation, sol gel method and conventional drying, and sol gel and supercritical drying techniques, three kinds of 20% Ni/Al2O3 catalysts have been prepared, the catalyst samples were characterized by means of BET, XRD, H2-TPR and H2-TPD. Catalytic performances of the different catalysts for CH4-CO2 reforming reaction were investigated in a micro fluidized bed reactor. Strong interaction between Ni species and support Al2O3 is found and NiO and spinel NiAl2O4 were formed in the aerogel catalyst, but weaker interaction is observed in the impregnation catalyst and xerogel catalyst. Among the catalysts examined, the aerogel catalyst exhibits high specific surface area, low bulk density, high Ni reduction degree and Ni dispersion degree. Excellent catalytic activity and stability were achieved via the combination of aerogel catalyst and fluidized bed reactor. The fluidization of aerogel porous agglomerates provides high bed expansion and long gas residence time, which remarkably improves the mass transfer. Thus the deposited carbon was quickly gasified and only a limited amount of carbon was formed on aerogel catalyst. For the impregnation catalyst and xerogel catalysts, low bed expansion and little particles circulation result worse efficiency of mass transfer and short gas residence time, which decrease the rate of carbon gasification, and thus result in the carbon deposition. The characterization revealed that massive graphite carbon deposition is the most important reason resulting in the deactivation of the impregnation catalyst and xerogel catalysts.