Foam/fiber-structured catalysts: non-dip-coating fabrication strategy and applications in heterogeneous catalysis
Foam/fiber-structured catalysts: non-dip-coating fabrication strategy and applications in heterogeneous catalysis
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DOI：
10.1007/s11434-016-1074-2
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发表时间：
2016-04
期刊：
影响因子：
18.9
通讯作者：
Guofeng Zhao;Ye Liu;Yong Lu
中科院分区：
文献类型：
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作者：
Guofeng Zhao;Ye Liu;Yong Lu
结构化催化剂和反应器(SCR)的开发和使用是克服传统固定床反应器的主要缺陷的一种很有前途的策略，这是由于流体力学的改善和强化传热传质相结合而引起的，因此成为多相催化领域的研究热点。其中最典型的可控硅催化剂之一是陶瓷蜂窝催化剂，广泛应用于汽车排放控制和电站氮氧化物减排。这种蜂窝催化剂包括数千个直径为毫米的开口平行通道(以提供高空隙分数，以便在高流速下通过催化剂床层的低压降)，并在通道壁上涂有微米厚度的催化涂层(由于气体扩散距离较短，从而改善了传质)。多年来，这种类型的SCR还发现了其他应用，如催化燃烧、部分氧化和液态加氢[1，2]。然而，使用整体蜂窝仍然具有挑战性，因为它们的传热相对较低，并且缺乏径向混合，这一点应该改进以用于内/外热和/或高通量反应[1]。在过去的十年中，金属纤维/泡沫塑料载体吸引了越来越多的兴趣[3]。除了典型的陶瓷蜂窝催化剂的高空隙率和内扩散外，它们独特的三维(3D)网络和开放结构以及高导热系数和机械强度使径向混合产生的反应物具有低压降、高传质/热传递，特别是高接触效率(图1)。此外，它们的金属特性具有独特的形状因素，在填充结构化反应堆时，在几何外观上提供了极大的灵活性。这些特性对于非常快速和受热/质传递控制的反应特别有利(图1)[4，5]。然而，纤维/泡沫塑料载体的催化功能化仍然具有挑战性，因为传统的涂层技术存在涂层不均匀和剥落以及粘结剂污染的问题。近年来，一系列有效、高效的非浸渍涂层方法被开发出来，用于纤维/泡沫结构的催化功能化。
Development and use of the structured catalysts and reactors (SCRs) is a promising strategy to overcome the major drawbacks encountered in the traditional packed-bed reactor due to improved hydrodynamics in the combination with enhanced heat/mass transfer, thus being a hot topic in the heterogeneous catalysis. One of the most typical SCRs is the ceramic honeycomb catalyst extensively applied in the control of automotive emissions and the reduction of nitrogen oxides from power stations. Such honeycomb catalyst consists of thousands of opening parallel channels in millimetric diameter (to offer high void fractions for low pressure drop at high flow rates through the catalyst bed) with catalytic washcoat in micrometric thickness on the channel walls (to improve mass transfer due to the short gas diffusion distance). Over the years, this type of SCRs has found other applications, such as catalytic combustion, partial oxidations and liquid-phase hydrogenations [1, 2]. However, using monolithic honeycomb still remains challenging because of their relatively lower heat transfer and the lack of radial mixing, which should be improved for the endo-/exo-thermic and/or high-throughput reactions [1]. Metal fiber/foam-based supports have attracted everincreasing interest within the last decade [3]. Besides the high voidage and internal-diffusion as typically in ceramic honeycomb catalysts, their unique three-dimensional (3D) network and open structure as well as high thermal conductivity and mechanical strength allow low pressure drop, high mass/heat transfer and especially high contacting efficiency of reactants resulted from the radial mixing (Fig. 1). Moreover, their metallic feature has unique form factors that provide a great flexibility in geometric appearance when filling up the structured reactors. These characteristics are particularly beneficial for very fast and heat/mass-transfer-controlled reactions (Fig. 1)[4, 5]. However, catalytic functionalization of the fiber/foambased supports remains challenging because the conventional washcoating technique suffers from nonuniformity and exfoliation of coatings as well as binder contamination. Recently, a series of effective and efficient non-dip-coating methods has been developed for catalytic functionalization of the fiber/foam structures.