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首页> 外文期刊>Catalysts >Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors
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Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors

机译：共组装的载体催化剂：通过组合流动和辐射诱导的共组装的纳米反应器合成具有分层孔的纳米结构的载体催化剂

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A novel generic method of silica supported catalyst system generation from a fluid state is presented. The technique is based on the combined flow and radiation (such as microwave, thermal or UV) induced co-assembly of the support and catalyst precursors forming nano-reactors, followed by catalyst precursor decomposition. The transformation from the precursor to supported catalyst oxide state can be controlled from a few seconds to several minutes. The resulting nano-structured micro-porous silica supported catalyst system has a surface area approaching 300 m 2 /g and X-ray Diffraction (XRD)-based catalyst size controlled in the range of 1–10 nm in which the catalyst structure appears as lamellar sheets sandwiched between the catalyst support. These catalyst characteristics are dependent primarily on the processing history as well as the catalyst (Fe, Co and Ni studied) when the catalyst/support molar ratio is typically 0.1–2. In addition, Ca, Mn and Cu were used as co-catalysts with Fe and Co in the evaluation of the mechanism of catalyst generation. Based on extensive XRD, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies, the micro- and nano-structure of the catalyst system were evaluated. It was found that the catalyst and silica support form extensive 0.6–2 nm thick lamellar sheets of 10–100 nm planar dimensions. In these lamellae, the alternate silica support and catalyst layer appear in the form of a bar-code structure. When these lamellae structures pack, they form the walls of a micro-porous catalyst system which typically has a density of 0.2 g/cm 3 . A tentative mechanism of catalyst nano-structure formation is provided based on the rheology and fluid mechanics of the catalyst/support precursor fluid as well as co-assembly nano-reactor formation during processing. In order to achieve these structures and characteristics, catalyst support must be in the form of silane coated silica nano-particles dispersed in water which also contains the catalyst precursor nitrate salt. This support-catalyst precursor fluid must have a sufficiently low viscosity but high elastic modulus (high extensional viscosity) to form films and bubbles when exposed to processing energy sources such as microwave, thermal, ultra-sound or UV-radiation or their combination. The micro-to-nano structures of the catalyst system are essentially formed at an early stage of energy input. It is shown that the primary particles of silica are transformed to a proto-silica particle state and form lamellar structures with the catalyst precursor. While the nano-structure is forming, water is evaporated leaving a highly porous solid support-catalyst precursor which then undergoes decomposition to form a silica-catalyst oxide system. The final catalyst system is obtained after catalyst oxide reduction. Although the XRD-based catalyst size changes slightly during the subsequent heat treatments, the nano-structure of the catalyst system remains substantially unaltered as evaluated through TEM images. However, if the catalyst preparation is carried out without film formation, the XRD-based catalyst size increases substantially by a factor of 2–8, with no significant alteration in surface area.
机译：提出了一种从流态生成二氧化硅负载的催化剂体系的新通用方法。该技术基于载体和催化剂前体形成纳米反应器的载体和催化剂前体的组合的流动和辐射（例如微波，热或UV）诱导的共组装，然后催化剂前体分解。从前体到负载的催化剂氧化物状态的转变可以控制在几秒钟到几分钟。所得的纳米结构微孔二氧化硅负载型催化剂体系的表面积接近300 m 2 / g，基于X射线衍射（XRD）的催化剂尺寸控制在1-10 nm范围内，其中催化剂结构为层状片夹在催化剂载体之间。当催化剂/载体的摩尔比通常为0.1–2时，这些催化剂的特性主要取决于加工历史以及催化剂（研究的Fe，Co和Ni）。此外，在评估催化剂生成机理时，将Ca，Mn和Cu与Fe和Co用作助催化剂。基于广泛的XRD，扫描电子显微镜（SEM）和透射电子显微镜（TEM）研究，对催化剂体系的微观和纳米结构进行了评估。结果发现，催化剂和二氧化硅载体形成了平面尺寸为10–100 nm的宽泛的0.6–2 nm厚片状片。在这些薄片中，交替的二氧化硅载体和催化剂层以条形码结构的形式出现。当这些片状结构堆积时，它们形成微孔催化剂体系的壁，该微孔催化剂体系的密度通常为0.2g / cm 3。基于催化剂/载体前体流体的流变学和流体力学以及在加工过程中共组装纳米反应器的形成，提供了催化剂纳米结构形成的初步机理。为了获得这些结构和特性，催化剂载体必须为分散在水中的硅烷涂覆的二氧化硅纳米颗粒的形式，所述二氧化硅还包含催化剂前体硝酸盐。该载体催化剂前体流体必须具有足够低的粘度，但必须具有足够高的弹性模量（高拉伸粘度），才能在暴露于诸如微波，热，超声或紫外线辐射等处理能源的环境下形成膜和气泡。催化剂体系的微纳结构基本上是在能量输入的早期阶段形成的。结果表明，二氧化硅的初级颗粒转变为原硅颗粒状态，并与催化剂前体形成层状结构。当形成纳米结构时，水被蒸发，留下高度多孔的固体载体-催化剂前体，然后其分解以形成二氧化硅-催化剂氧化物体系。在催化剂氧化物还原之后获得最终的催化剂体系。尽管基于XRD的催化剂尺寸在随后的热处理过程中略有变化，但通过TEM图像评估，催化剂体系的纳米结构基本上保持不变。但是，如果催化剂制备没有成膜，则基于XRD的催化剂尺寸将增加2-8倍，而表面积没有明显变化。

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