Probing dynamics of noble metal nanoparticles under reaction conditions

Supported noble metal nanoparticles (NPs), including Pt, Pd, and PtPd alloys on Al2O3 or CeO2, are pivotal in heterogeneous catalysis for emission control. Maximizing the economic efficiency of these costly metals necessitates catalysts with high activity over their lifetime. A primary challenge to maintaining activity is thermal deactivation via sintering. Two fundamental sintering mechanisms, namely Oswald ripening (OR) and particle migration and coalescence (PMC), have already been identified in the literature.  However, recently there has been an ongoing debate about surface vs gas-phase mediated sintering pathways [Ple-16][Oh-23]. To help address this open question we aim to capture real-time, statistically significant data to provide insights into the dynamics of chosen NP/support systems under reactive conditions on a broad micrometer scale using electron microscopy.

While in situ catalysis experiments using electron microscopy were previously carried out only in transmission electron microscopes (TEM) equipped with special holders for heating or gas experiments, allowing the study of single nanoparticles with atomic resolution, recently environmental scanning electron microscopes (ESEM) have become a popular tool to study dynamic catalytic behavior on a broader micrometer scale [Bar-19].

In this work we will introduce our novel in situ experimental setup inside an ESEM using a heating stage, capable of temperatures of up to 1000°C and a self-build gas injection system, thereby enabling the study of large populations of supported NPs and their reaction to experimental stimuli. This experimental setup coupled with an automatic post-processing routine based on computer vision algorithms allows the analysis of long time series of recorded images and permits a statistical evaluation of the NP motion trajectories, thus providing insight into the sintering behavior of these NPs as a function of temperature and gas atmosphere.

We will present the first preliminary results of our experimental setup under simplified oxidation conditions of 10mol-% O2 in N2, as well as reduction conditions of 5mol-% H2 in N2 at various temperatures for different NP/support systems. Following up from a previous study in which we analyzed the redispersion mechanism of Pt/CeO2 under alternating oxidation/reduction cycles ex situ, we will present the results of this redispersion experiment in our new ESEM setup, as well as ex situ characterization of the CeO2 support substrates used in this work [Sch-24]. In addition, we will present our data post-processing routines and discuss some challenges.

Literature

[Oh-23] J. Oh, A. Beck, E. D. Goodman, L. T. Roling, A. Boucly, L. Artiglia, F. Abild-Pedersen, J. A. Van Bokhoven, M. Cargnello, ACS Catal. 2023, 13 (3), 1812–1822. DOI: 10.1021/acscatal.2c04683.

[Bar-19] C. Barroo, Z.-J. Wang, R. Schlögl, M.-G. Willinger,  Nat. Catal. 2019, 3 (1), 30–39. DOI: 10.1038/s41929-019-0395-3.

[Ple-16] P. N. Plessow, F. Abild-Pedersen, ACS Catal. 2016, 6 (10), 7098–7108. DOI: 10.1021/acscatal.6b01646.

[Sch-24] J.-C. Schober, E. E. Beck, M.-C. Kao, M. Kohantorabi, M. Creutzburg, D. Novikov, B. Holtermann, N. Firman, L. Caulfield, E. Sauter, V. Vonk, C. Wöll, Y. Wang, H. Noei, Y. Eggeler, A. Stierle, March 26, 2024. DOI: 10.26434/chemrxiv-2024-r58cx.