Colloidally Engineered Pd and Pt Catalysts Distinguish Surface- and Vapor-Mediated Deactivation Mechanisms
Colloidally Engineered Pd and Pt Catalysts Distinguish Surface- and Vapor-Mediated Deactivation Mechanisms
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DOI：
10.1021/acscatal.2c04683
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发表时间：
2023-01
期刊：
影响因子：
12.9
通讯作者：
Jinwon Oh;A. Beck;E. Goodman;Luke T. Roling;A. Boucly;L. Artiglia;F. Abild-Pedersen;J. V. van Bokhoven;M. Cargnello
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作者：
Jinwon Oh;A. Beck;E. Goodman;Luke T. Roling;A. Boucly;L. Artiglia;F. Abild-Pedersen;J. V. van Bokhoven;M. Cargnello
贵金属基催化剂因其高活性和稳定性而广泛应用。然而，随着时间的推移，它们会不可逆转地恶化，尤其是在高温应用中。在这些条件下，烧结是失活的主要原因，了解烧结是如何发生的，可以减轻这些有害的过程。先前的研究成功地区分了两种基本的烧结模式，即颗粒迁移和聚结（PMC）和奥斯特瓦尔德成熟（OR）。然而，表面和蒸汽介导的奥斯特瓦尔德成熟过程之间的差异尚未得到证实，尽管它是调整金属/载体相互作用和稳定催化剂的关键信息。在这里，我们证明了表面和蒸汽介导的成熟发生在两种不同的温度下，并且使用由胶体纳米晶体制备的Pt和Pd催化剂作为前驱体有一些重叠。通过将两种金属纳米晶体共浸渍在同一颗粒的氧化铝载体上，或者通过物理混合两种不同金属催化剂的粉末，我们调整了纳米和微米之间的金属间颗粒距离。然后，我们使用甲烷完全氧化作为报告反应，在纯Pd上以较高的速率发生，在合金Pd/Pt催化剂上以较低的速率发生，以跟踪系统中Pt的运动。在不同的温度下老化催化剂，我们发现Pt最初是通过表面介导的成熟烧结到~ 750℃，但在800℃以上的温度下，由pt2蒸汽介导的成熟成为主要的烧结机制。这项工作证明了胶体催化剂如何允许对支持系统的工作和失活机制有独特的见解。
Noble metal-based catalysts are ubiquitous because of their high activity and stability. However, they irreversibly deteriorate over time especially in high-temperature applications. In these conditions, sintering is the main reason for deactivation, and understanding how sintering occurs gives the opportunity to mitigate these detrimental processes. Previous studies successfully distinguished between two fundamental sintering modes, namely, particle migration and coalescence (PMC) and Ostwald ripening (OR). However, differentiation between surface- and vapor-mediated Ostwald ripening processes has not been demonstrated yet, even though it is crucial information to tune metal/support interactions and stabilize catalysts. Here, we demonstrate that surface- and vapor-mediated ripening occur in two distinct regimes of temperature with some overlap using Pt and Pd catalysts prepared from colloidal nanocrystals as precursors. By either co-impregnating the two metal nanocrystals on the same grain of alumina support or by physically mixing powders of the two distinct metal catalysts, we tune the intermetal particle distance between nanometers and micrometers. We then use methane complete oxidation as a reporter reaction that occurs at higher rates on pure Pd and lower rates on alloyed Pd/Pt catalysts to trace the movement of Pt in the system. Aging the catalysts at different temperatures allows us to reveal that Pt initially sinters by surface-mediated ripening until ∼750 °C, but at temperatures above 800 °C, vapor-mediated ripening by PtO2becomes the main sintering mechanism. This work demonstrates how colloidal catalysts allow unique insights into the working and deactivation mechanisms of supported systems.