Operando Studies of Aerosol-Assisted Sol-Gel Catalyst Synthesis via Combined Optical Trapping and Raman Spectroscopy
Operando Studies of Aerosol-Assisted Sol-Gel Catalyst Synthesis via Combined Optical Trapping and Raman Spectroscopy
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DOI：
10.1021/acs.jpcc.1c07517
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发表时间：
2021-10-13
影响因子：
3.7
通讯作者：
McGregor, James
中科院分区：
文献类型：
--
作者：
Davies, Gareth;Driver, Justin;McGregor, James
对气溶胶辅助溶胶-凝胶（AASG）合成催化剂的初始阶段发生的化学转化有了新的认识。这是通过光阱和拉曼光谱的组合应用实现的。AASG是一种新兴的催化剂制造技术，与传统方法相比具有许多优点，包括能够获得独特的催化剂形态。然而，在合成过程中发生的过程很大程度上是从体相分析推断，由于在流管内移动的气溶胶进行原位或操作性测量的挑战。在此，这些障碍通过对限制在光学陷阱内的单个气溶胶液滴的拉曼光谱询问来克服，光学陷阱充当沿着流管移动的颗粒的直接模拟物。这些研究代表了AASG合成的第一个操作性研究。已经研究了Ni/Al 2 O3催化剂的合成，其中对前体合成溶液的每种组分进行光谱询问，在可能的情况下，直到并包括含有催化剂合成所需的所有组分的混合物。拉曼光谱证实了在气溶胶内形成稳定的自组装宏观结构，并提供了对反应机制的直接见解。至关重要的是，获得的证据允许替代的反应途径被假定在密闭的环境中的气溶胶液滴相比，体相合成。在气溶胶中镍不存在，但含有所有其他成分，等温室温研究表明，形成稳定的，但不活泼的液滴类似于1 μ m，这被认为是含有胶束型结构。在加热时，观察到在高于类似于56 ℃的温度下实现初始凝胶化转变。值得注意的是，从加热的气溶胶中观察到对应于C-H伸缩（乙醇）的光谱强度几乎没有损失，这意味着蒸发不是反应的先决条件。当镍存在于合成溶液中时，在室温下发生反应性转变，提出产生连续的Al-O-Ni-NO3结构;在升高的温度下发生更快速的转变。这些结果提供了AASG期间气溶胶内发生的过程的第一个直接证据，并为这项技术的机理理解提供了新的思路。因此，这有助于设计新的合成方法，从而生产具有增强性能的催化剂和其他材料。
New insights have been gained into chemical transformations occurring in the initial stages of aerosol-assisted sol-gel (AASG) synthesis of catalysts. This has been achieved through the combined application of optical trapping and Raman spectroscopy. AASG is an emerging technology in catalyst manufacturing that presents numerous advantages over conventional approaches, including the ability to access unique catalyst morphologies. However, the processes occurring during synthesis are largely inferred from bulk-phase analyses due to challenges in conducting in situ or operando measurements on moving aerosols within a flow tube. Herein, these obstacles are overcome through Raman spectroscopic interrogation of a single aerosol droplet constrained within an optical trap, which acts as a direct analogue for a particle moving along a flow tube. These studies represent the first operando investigations of AASG synthesis. The synthesis of Ni/Al2O3 catalysts has been studied, with spectroscopic interrogation conducted on each component of the precursor synthesis solution, where possible, up to and including a mixture containing all components necessary for catalyst synthesis. Raman spectroscopy confirms the formation of stable self-assembled macrostructures within the aerosol and provides direct insights into the reaction mechanisms. Crucially, evidence was obtained allowing alternative reaction pathways to be postulated within the confined environment of an aerosol droplet in comparison to bulk-phase syntheses. In aerosols where nickel was not present, but contained all other components, isothermal room-temperature studies showed the formation of stable but unreactive droplets of similar to 1 mu m, which were proposed to contain micelle-type structures. Upon heating, initial gelation transformations were seen to be achieved at temperatures higher than similar to 56 degrees C. Notably, little loss of spectral intensity corresponding to the C-H stretch (ethanol) was observed from the heated aerosol, implying that evaporation is not a prerequisite for the reaction. When nickel is present in the synthesis solution reactive transformations occur at room temperature, proposed to result in a continuous Al-O-Ni-NO3 structure; a more rapid transformation takes place at elevated temperatures. These results provide the first direct evidence of the processes occurring within aerosols during AASG and shed new light on the mechanistic understanding of this technology. This therefore facilitates the design of new synthetic approaches and hence the production of catalysts and other materials with enhanced properties.