Institute of Applied and Physical Chemistry, University of Bremen, Germany; Center for Environmental Research and Sustainable Technology and MAPEX Center for Materials and Processes, University of Bremen, Germany.
Institute of Chemistry, Carl v. Ossietzky University of Oldenburg, Germany.
J Colloid Interface Sci. 2016 Sep 1;477:64-73. doi: 10.1016/j.jcis.2016.05.006. Epub 2016 May 10.
The application of catalytically coated metallic foams in catalytic processes has a high potential for exothermic catalytic reactions such as CO2 methanation or Fischer-Tropsch synthesis due to good heat conductivity, improved turbulent flow properties and high catalyst efficiencies. But the preparation of homogenous catalyst coats without pore blocking is challenging with conventional wash coating techniques. Here, we report on a stable and additive free colloidal CoAlOOH suspension (sol) for the preparation of catalytically active Co/Al2O3 xerogel catalysts and coatings. Powders with 18wt% Co3O4 prepared from this additive free synthesis route show a catalytic activity in Fischer-Tropsch synthesis and CO2 methanation which is similar to a catalyst prepared by incipient wetness impregnation (IWI) after activating the material under flowing hydrogen at 430°C. Yet, the xerogel catalyst exhibits a much higher thermal stability as compared to the IWI catalyst, as demonstrated in catalytic tests after different heat agings between 430°C and 580°C. It was also found that the addition of polyethylene glycol (PEG) to the sol influences the catalytic properties of the formed xerogels negatively. Only non-reducible cobalt spinels were formed from a CoAlOOH sol with 20wt% PEG. Metallic foams with pores sizes between 450 and 1200μm were coated with the additive free CoAlOOH sol, which resulted in homogenous xerogel layers. First catalytic tests of the coated metal foams (1200μm) showed good performance in CO2 methanation.
催化涂层金属泡沫在催化过程中的应用对于放热催化反应（如 CO2 甲烷化或费托合成）具有很高的潜力，因为其具有良好的导热性、改善的湍流流动特性和高催化剂效率。但是，使用传统的洗涤涂层技术，在没有堵塞孔的情况下制备均匀的催化剂涂层是具有挑战性的。在这里，我们报告了一种稳定的、无添加剂的胶体 CoAlOOH 悬浮液（溶胶），用于制备催化活性 Co/Al2O3 气凝胶催化剂和涂层。由无添加剂合成路线制备的 18wt% Co3O4 粉末在费托合成和 CO2 甲烷化中的催化活性与在 430°C 下在流动氢气中活化后用初始润湿浸渍（IWI）制备的催化剂相当。然而，与 IWI 催化剂相比，气凝胶催化剂表现出更高的热稳定性，这在 430°C 和 580°C 之间进行不同热老化后的催化测试中得到了证明。还发现，向溶胶中添加聚乙二醇（PEG）会对形成的气凝胶的催化性能产生负面影响。只有在添加 20wt%PEG 的 CoAlOOH 溶胶中才会形成不可还原的钴尖晶石。孔径为 450 至 1200μm 的金属泡沫用无添加剂的 CoAlOOH 溶胶进行了涂层处理，从而形成了均匀的气凝胶层。涂覆金属泡沫（1200μm）的首次催化测试表明在 CO2 甲烷化中表现出良好的性能。
