Insights into the reaction mechanism and particle size effects of CO oxidation over supported Pt nanoparticle catalysts
Insights into the reaction mechanism and particle size effects of CO oxidation over supported Pt nanoparticle catalysts
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DOI：
10.1016/j.jcat.2019.07.049
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发表时间：
2019-09-01
影响因子：
7.3
通讯作者：
Kunz, Sebastian
中科院分区：
文献类型：
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作者：
Neumann, Sarah;Gutmann, Torsten;Kunz, Sebastian
CO氧化反应是多相催化反应中研究最多的一个反应，由于其表面上的简单性和对排放控制的重要性。然而，颗粒尺寸和更具体的结构敏感性在该反应中的作用仍然是有争议的。在本研究中，胶体的“无表面活性剂”的Pt纳米粒子（NPs）的尺寸范围为1-4 nm的窄尺寸分布和控制粒度合成，随后负载在氧化铝上制备模型催化剂。在不同的反应温度下，使用粒径为1、2、3和4 nm的Pt NPs催化剂进行CO氧化。结果表明，该反应表现出强烈依赖于反应条件的颗粒尺寸效应。在170 ℃下，对于所有粒径，反应似乎在相同的动力学范围内进行，但表面归一化活性强烈依赖于粒径，直径为2 nm的纳米颗粒的活性最大。温度升高到200摄氏度导致取决于颗粒尺寸的动力学状态的变化。对于直径为1 nm的Pt NPs，观察到O-2的反应级数为1，表明O-2分子吸附并在随后的步骤中解离，这代表了Pt表面上普遍接受的机制。CO的反应级数为-1，表明在反应条件下表面被CO饱和。随着粒径的增大，O-2和CO的反应级数发生变化。对于粒径为2 nm的颗粒，温度升高也会导致O-2的反应级数为1，CO的反应级数为-1;即使在更高的温度下，3和4 nm的NP也没有显示出可以通过单一反应机制解释的明确动力学行为。相反，两个相邻的吸附CO分子之间的Boudouard反应被确定为一个重要的额外的反应途径，优先发生在大颗粒，并导致更复杂的动力学。(C)2019爱思唯尔公司All rights reserved.
CO oxidation is an extensively studied reaction in heterogeneous catalysis due to its seeming simplicity and its great importance for emission control. However, the role of particle size and more specifically structure sensitivity in this reaction is still controversial. In the present study, colloidal "surfactant-free" Pt nanoparticles (NPs) in a size regime of 1-4 nm with narrow size distribution and control over particle size were synthesized and subsequently supported on Al2O3 to prepare model catalysts. CO oxidation was performed using Pt NPs catalysts with particles sizes of 1, 2, 3, and 4 nm at different reaction temperatures. It is shown that the reaction exhibits a particle size effect that depends strongly on the reaction conditions. At 170 degrees C, the reaction seems to proceed within the same kinetic regime for all particle sizes, but the surface normalized activity depends strongly on the particle size, with maximum activity for nanoparticles 2 nm in diameter. A temperature increase to 200 degrees C leads to a change of the kinetic regime that depends on the particle size. For Pt NPs 1 nm in diameter a reaction order of 1 for O-2 was observed, indicating that O-2 adsorbs molecularly and dissociates in a following step, which represents the generally accepted mechanism on Pt surfaces. The reaction order of -1 for CO demonstrates that the surface is saturated with CO under reaction conditions. With increasing particle size, the reaction orders of O-2 and CO change. For particles 2 nm in size, an increase in temperature also results in reaction orders of 1 for O-2 and -1 for CO; NPs of 3 and 4 nm, even at higher temperatures, show no clear kinetic behavior that can be explained by a single reaction mechanism. Instead, the Boudouard reaction between two adjacent adsorbed CO molecules was identified as an important additional reaction pathway that occurs preferentially on large particles and causes more complex kinetics. (C) 2019 Elsevier Inc. All rights reserved.