Jie Xiangyu, Chen Roujia, Biddle Tara, Slocombe Daniel R, Dilworth Jonathan Robin, Xiao Tiancun, Edwards Peter P
Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
School of Engineering, Cardiff University, Queen's Buildings, The Parade, Cardiff CF24 3AA, United Kingdom.
Chem Mater. 2022 May 24;34(10):4682-4693. doi: 10.1021/acs.chemmater.2c00630. Epub 2022 May 13.
Knowledge of the electromagnetic microwave radiation-solid matter interaction and ensuing mechanisms at active catalytic sites will enable a deeper understanding of microwave-initiated chemical interactions and processes, and will lead to further optimization of this class of heterogeneous catalysis. Here, we study the fundamental mechanism of the interaction between microwave radiation and solid Fe catalysts and the deep dehydrogenation of a model hydrocarbon, hexadecane. We find that the size-dependent electronic transition of particulate Fe metal from a microwave "reflector" to a microwave "absorber" lies at the heart of efficient metal catalysis in these heterogeneous processes. In this regard, the optimal particle size of a Fe metal catalyst for highly effective microwave-initiated dehydrogenation reactions is approximately 80-120 nm, and the catalytic performance is strongly dependent on the ratio of the mean radius of Fe particles to the microwave skin depth (/δ) at the operating frequency. Importantly, the particle size of selected Fe catalysts will ultimately affect the basic heating properties of the catalysts and decisively influence their catalytic performance under microwave initiation. In addition, we have found that when two or more materials-present as a mechanical mixture-are simultaneously exposed to microwave irradiation, each constituent material will respond to the microwaves independently. Thus, the interaction between the two materials has been found to have synergistic effects, subsequently contributing to heating and improving the overall catalytic performance.
了解电磁微波辐射与固体物质在活性催化位点的相互作用及后续机制，将有助于更深入地理解微波引发的化学相互作用和过程，并将推动这类多相催化的进一步优化。在此，我们研究了微波辐射与固体铁催化剂之间相互作用的基本机制以及模型烃十六烷的深度脱氢反应。我们发现，在这些多相过程中，颗粒状铁金属从微波“反射体”到微波“吸收体”的尺寸依赖性电子跃迁是高效金属催化的核心。在这方面，用于高效微波引发脱氢反应的铁金属催化剂的最佳粒径约为80 - 120纳米，催化性能强烈依赖于铁颗粒的平均半径与工作频率下微波趋肤深度（/δ）的比值。重要的是，所选铁催化剂的粒径最终会影响催化剂的基本加热特性，并决定性地影响其在微波引发下的催化性能。此外，我们发现当两种或更多种以机械混合物形式存在的材料同时受到微波辐射时，每种组成材料会独立地对微波作出响应。因此，已发现这两种材料之间的相互作用具有协同效应，随后有助于加热并提高整体催化性能。
