Wang Hongjing, Teng Yonghong, Radhakrishnan Logudurai, Nemoto Yoshihiro, Imura Masataka, Shimakawa Yuichi, Yamauchi Yusuke
World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
J Nanosci Nanotechnol. 2011 May;11(5):3843-50. doi: 10.1166/jnn.2011.3836.
Mesoporous Co3O4 particles are prepared by using mesoporous silica KIT-6 (with double gyroid Ia-3d symmetry) as a hard-template and Co(No3)2 x 6H2O as an inorganic precursor. In the former section, we investigate the effect of the calcination temperatures at which the Co salts are converted into Co3O4 inside the mesopores on the textural parameters of the products. The results of N2 adsorption-desorption analysis indicates that the calcination temperatures do not obviously affect the textural parameters such as the surface areas and pore volumes. However, when the calcination temperature reaches 800 degrees C, the mesostructural ordering is dramatically decreased, resulting in the reduction of the surface areas and pore volumes. After 800 degrees C calcination, the formation of large Co3O4 grains is partially confirmed on the particle surface by SEM observation. The grain size is much larger than the mesopore size of the original KIT-6, meaning the crystal growth is continuously occurred by breaking the rigid silica frameworks. In the latter section, we discuss the effect of the calcination temperatures and textural parameters on the catalytic activity for CO oxidation by both steady state and kinetic measurements. All mesoporous Co3O4 particles show a high catalytic activity, for example, -72 degrees C for sample calcined at 450 degrees C. Only 10 degrees C difference in T50 (the temperature of 50% conversion of CO) is found between the samples with the highest and lowest catalytic activity. The values of activation energy (Ea) and pre-exponential factor (A) per unit area are almost the same between two samples calcined at 450 degrees C and 800 degrees C. It is demonstrated that calcination process can not alter the essential catalytic property of mesoporous Co3O4 particles.
介孔Co3O4颗粒是通过使用介孔二氧化硅KIT-6（具有双螺旋体Ia-3d对称性）作为硬模板和Co(No3)2·6H2O作为无机前驱体制备的。在前一部分中，我们研究了介孔内Co盐转化为Co3O4时的煅烧温度对产物结构参数的影响。N2吸附-脱附分析结果表明，煅烧温度对表面积和孔体积等结构参数没有明显影响。然而，当煅烧温度达到800℃时，介观结构有序度急剧下降，导致表面积和孔体积减小。在800℃煅烧后，通过扫描电子显微镜观察在颗粒表面部分确认了大的Co3O4晶粒的形成。晶粒尺寸远大于原始KIT-6的介孔尺寸，这意味着通过破坏刚性二氧化硅骨架，晶体生长持续发生。在后一部分中，我们通过稳态和动力学测量讨论了煅烧温度和结构参数对CO氧化催化活性的影响。所有介孔Co3O4颗粒都表现出高催化活性，例如，450℃煅烧的样品为-72℃。催化活性最高和最低的样品之间的T50（CO转化率为50%时的温度）仅相差10℃。在450℃和800℃煅烧的两个样品之间，单位面积的活化能（Ea）和指前因子（A）值几乎相同。结果表明，煅烧过程不会改变介孔Co3O4颗粒的基本催化性能。
