甲烷干重整催化剂Ni/Al2O3表面积炭表征与分析

用蒸发法制备了Ni/Al2O3催化剂及浸渍法制备了Ni/α-Al2O3和Ni/γ-Al2O3催化剂, 并与商品天然气水蒸气重整催化剂Z118Y一起进行了甲烷干重整实验, 考察了各催化剂上表面积炭行为. 通过H2程序升温还原(H2-TPR)、BET(Brunauer-Emmett-Teller)比表面积分析、X射线衍射(XRD)、透射电镜(TEM)、热重-差式扫描量热(TG-DSC)、程序升温氢化(TPH)等表征手段对催化剂表面沉积炭的特性进行了表征. 结果表明, 各催化剂上至少存在三种形式的碳物种: 无定形碳、丝状碳及石墨碳. 由于载体性质不同, 各催化剂上沉积炭的种类及其含量有所差别. Z118Y、Ni/Al2O3及Ni/α-Al2O3催化剂上主要沉积丝状炭, 而Ni/γ-Al2O3催化剂上则主要是石墨碳. Ni/γ-Al2O3催化剂中金属Ni颗粒较小(小于15 nm)、粒径分布范围较窄、分散性较好, 能减少催化剂表面炭的沉积, 有效地抑制丝状碳的生长.

Characterization and Analysis of Carbon Deposited on the Surface of Ni/Al2O3 Catalyst for Methane Dry Reforming

Ni/Al2O3 catalyst was prepared by evaporation method. Ni/α-Al2O3 and Ni/γ-Al2O3 catalysts were prepared using traditional incipient wetness impregnation. Dry reforming of methane over the prepared catalysts and the commercial catalyst Z118Y for steam reforming of natural gas was investigated. Properties of the carbon species deposited on the surface of the catalysts were characterized by H2-temperature programmed reduction (H2-TPR), Brunauer-Emmett-Teller (BET) specific surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry-differential scanning calorimetry (TG-DSC), and temperature programmed hydrogenation (TPH). The results showed that there are three main carbon species on the surface of the catalysts, namely amorphous, filamentous, and graphitic carbon. In addition, the content of carbon deposited on these catalysts varied because of different structures and properties of alumina. Filamentous carbon (namely carbon nanotubes) was the main species deposited on catalysts Z118Y, Ni/Al2O3, and Ni/α-Al2O3 while the graphitic carbon species was dominant on the Ni/γ-Al2O3 catalyst. Furthermore, the particle size of nickel on the Ni/γ-Al2O3 catalyst was small (less than 15 nm) and narrowly distributed while it also showed a high dispersion of metallic nickel on the support. It is recognized that the high dispersion of nickel particles would not only decrease the deposition of carbon on the surface of the catalyst but also depress the growth of filamentous carbon effectively.