The energy efficiency of heterogeneous catalytic processes may be improved by using mid-infrared light to excite gas-phase reactants during the reaction, since vibrational excitation of molecules has been shown to increase their reactivity at the gas-catalyst interface. A primary challenge for such light-enabled catalysis is the need to ensure close coupling between light-excited molecules and the catalyst throughout the reactor. Thus, it is imperative to understand how to couple infrared light efficiently to molecules near and inside catalytic material. Heterogenous catalysts are often nanoscale metal particles supported on high surface area, porous oxide materials and exhibit feature sizes across multiple scattering regimes with respect to the mid-infrared wavelength. These complex powders make a direct measurement of the scattering properties challenging. Here, we demonstrate that a combination of directional hemispherical measurements along with the in-line transmission measurement allow for a direct measurement of the scattered light signal. We implement this technique to study the scattering behavior of the catalytic support material γ-Al2O3 (with and without metal loading) between 1040 and 1220 cm-1. We first study how both the mean grain size affects the scattering behavior by comparing three different mean grain sizes spanning three orders of magnitude (2, 40, and 900 μm). Furthermore, we study how the addition of metal catalyst nanoparticles, Ru or Cu, to the support material impacts the light scattering behavior of the powder. We find that the 40 μm grain size scatters the most (up to 97% at 1220 cm-1) and that the addition of metal nanoparticles narrows the scattering angle but does not decrease the scattering efficiency. The strong scattering of the 40 μm grains make them the most ideal support material of those studied for the given spectrum because of their ability to distribute light within the reactor. Lastly, we estimate that less than 100 mW of laser power is needed to cause significant excitation for testing mid-infrared catalysis in a Harrick Praying MantisTMï diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reactor, a magnitude easily available using commercial mid-infrared lasers. Our work also provides a mid-infrared foundation for a wide range of studies of light-enabled catalysis and can be extended to other wavelengths of light or to study the scattering behavior of other complex powders in other fields, including ceramics, biomaterials, and geology.

中文翻译：

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EXPRESS：γ-Al ₂ O ₃催化粉末中的中红外散射

多相催化过程的能量效率可以通过在反应过程中使用中红外光激发气相反应物来提高，因为分子的振动激发已被证明可以增加它们在气体-催化剂界面的反应性。这种光催化的主要挑战是需要确保整个反应器中光激发分子和催化剂之间的紧密耦合。因此，必须了解如何将红外光有效地耦合到催化材料附近和内部的分子。多相催化剂通常是负载在高表面积多孔氧化物材料上的纳米级金属颗粒，并且在中红外波长的多个散射范围内表现出特征尺寸。这些复杂的粉末使散射特性的直接测量具有挑战性。在这里，我们证明了定向半球测量与在线传输测量的组合允许直接测量散射光信号。我们实施此技术来研究 1040 和 1220 cm-1 之间催化支持材料 γ-Al2O3（有和没有金属负载）的散射行为。我们首先通过比较跨越三个数量级（2、40 和 900 μm）的三种不同平均晶粒尺寸来研究平均晶粒尺寸如何影响散射行为。此外，我们研究了向载体材料中添加金属催化剂纳米粒子 Ru 或 Cu 如何影响粉末的光散射行为。我们发现 40 μm 晶粒尺寸散射最多（在 1220 cm-1 处高达 97%），并且添加金属纳米粒子会缩小散射角，但不会降低散射效率。40 μm 颗粒的强烈散射使它们成为针对给定光谱研究的那些材料中最理想的支撑材料，因为它们能够在反应器内分配光。最后，我们估计在 Harrick Praying MantisTM 漫反射红外傅里叶变换光谱 (DRIFTS) 反应器中测试中红外催化作用需要不到 100 mW 的激光功率来引起显着激发，使用商用中红外激光器很容易获得这个量级.