Ni / Al2O3催化剂在近室温下的等离子体增强氨合成催化作用：深入了解催化剂表面对反应机理的重要性。,ACS Catalysis

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Ni / Al2O3催化剂在近室温下的等离子体增强氨合成催化作用：深入了解催化剂表面对反应机理的重要性。
ACS Catalysis ( IF 11.3 ) Pub Date : 2019-10-18 , DOI: 10.1021/acscatal.9b02538
Yaolin Wang ₁ , Michael Craven ₁ , Xiaotong Yu ₁ , Jia Ding ₂ , Paul Bryant ₁ , Jun Huang ₂ , Xin Tu ₁

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对等离子体-催化剂相互作用和反应机理的更好的基本了解对于优化通过等离子体催化合成氨的催化剂的设计至关重要。在这项工作中，我们报告了一种混合等离子体增强的催化工艺，该工艺在接近室温（约35°C）的条件下，通过过渡金属催化剂（M / Al2O3，M = Fe，Ni，Cu）直接由N2和H2合成氨）和大气压。反应是在特别设计的同轴电介质阻挡放电（DBD）等离子体反应器中进行的，使用水作为接地电极，该反应器可以冷却并保持反应在室温附近。水电极的透明性使整个等离子体放电区域的操作光学诊断（增强的电荷耦合器件（ICCD）成像和光学发射光谱）得以进行，而无需改变反应堆的运行，这在使用同轴反应堆时经常需要带有不透明的接地电极。与没有催化剂的NH3的等离子体合成相比，等离子体催化显着提高了NH3的合成速率和能效。不同的过渡金属催化剂对放电物的物理性能的影响可以忽略不计，这表明在氨的等离子体催化合成中，由催化剂表面化学性质提供的催化作用比催化剂的物理作用更占优势。使用Ni / Al2O3作为等离子体催化剂，可获得最高的NH3合成速率，为471μmolg-1 h-1，这比仅使用等离子体获得的NH3合成速率高100％。Al 2 O 3的表面上存在过渡金属（例如，Ni）比仅Al 2 O 3或等离子体提供更均匀的等离子体放电，并提高了平均电子能。通过操作性等离子体诊断结合使用N2物理吸附测量，X射线光电子能谱（XPS），X射线衍射（XRD），高分辨率透射电子显微镜对催化剂进行全面表征，研究了等离子体催化氨合成的机理。（HRTEM），NH3温度程序解吸（TPD）和N2-TPD。使用XPS在废催化剂的表面上检测到四种形式的NH x吸附物种（x = 0、1、2和3）。

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Plasma-Enhanced Catalytic Synthesis of Ammonia over a Ni/Al2O3 Catalyst at Near-Room Temperature: Insights into the Importance of the Catalyst Surface on the Reaction Mechanism.

A better fundamental understanding of the plasma-catalyst interaction and the reaction mechanism is vital for optimizing the design of catalysts for ammonia synthesis by plasma-catalysis. In this work, we report on a hybrid plasma-enhanced catalytic process for the synthesis of ammonia directly from N2 and H2 over transition metal catalysts (M/Al2O3, M = Fe, Ni, Cu) at near room temperature (∼35 °C) and atmospheric pressure. Reactions were conducted in a specially designed coaxial dielectric barrier discharge (DBD) plasma reactor using water as a ground electrode, which could cool and maintain the reaction at near-room temperature. The transparency of the water electrode enabled operando optical diagnostics (intensified charge-coupled device (ICCD) imaging and optical emission spectroscopy) of the full plasma discharge area to be conducted without altering the operation of the reactor, as is often needed when using coaxial reactors with opaque ground electrodes. Compared to plasma synthesis of NH3 without a catalyst, plasma-catalysis significantly enhanced the NH3 synthesis rate and energy efficiency. The effect of different transition metal catalysts on the physical properties of the discharge is negligible, which suggests that the catalytic effects provided by the chemistry of the catalyst surface are dominant over the physical effects of the catalysts in the plasma-catalytic synthesis of ammonia. The highest NH3 synthesis rate of 471 μmol g-1 h-1 was achieved using Ni/Al2O3 as a catalyst with plasma, which is 100% higher than that obtained using plasma only. The presence of a transition metal (e.g., Ni) on the surface of Al2O3 provided a more uniform plasma discharge than Al2O3 or plasma only, and enhanced the mean electron energy. The mechanism of plasma-catalytic ammonia synthesis has been investigated through operando plasma diagnostics combined with comprehensive characterization of the catalysts using N2 physisorption measurements, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), NH3-temperature-programmed desorption (TPD), and N2-TPD. Four forms of adsorbed NH x (x = 0, 1, 2, and 3) species were detected on the surfaces of the spent catalysts using XPS. It was found that metal sites and weak acid sites could enhance the production of NH3 via formation of NH2 intermediates on the surface.

更新日期：2019-11-01

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