Probing the Thermal Stability of (3‐Mercaptopropyl)‐trimethoxysilane‐Protected Au₂₅ Clusters by In Situ Transmission Electron Microscopy

Abstract

High‐surface‐area gold catalysts are promising catalysts for a number of selective oxidation and reduction reactions but typically suffer catalyst deactivation at higher temperatures. The major reason for catalyst deactivation is sintering, which can be triggered via two mechanisms: particle migration and coalescence, and Ostwald ripening. Herein, a direct method to synthesize Au25 clusters stabilized with 3‐mercaptopropyltrimethoxysilane (MPTS) ligands is discussed. The sintering of Au25(MPTS)18 clusters on mesoporous silica (SBA‐15) is monitored by using an environmental in situ transmission electron microscopy (TEM) technique. Results show that agglomeration of smaller particles is accelerated by increased mobility of particles during heat treatment, while growth of immobile particles occurs via diffusion of atomic species from smaller particles. The mobility of the Au clusters can be alleviated by fabricating overlayers of silica around the clusters. The resulting materials show tremendous sinter‐resistance at temperatures up to 650 °C as shown by in situ TEM and extended X‐ray absorption fine structure analysis.

Taking a different road: following Ag25 and Au25 cluster activation via in situ differential pair distribution function analysis

“…As reported elsewhere for a similar Au system, the consequence of ligand desorption is particle migration and coalescence, which then leads to Au particle growth at higher temperatures. 55 For calcination temperatures of 100 1C and beyond, the Au-S peak and Au-Au cluster peaks observed for intact Au 25 (SR) 18 À clusters disappear, with consequent emergence of peaks at 2.83 Å, 4.02 Å, 4.89 Å, 5.64 Å, 6.33 Å, 6.92 Å, 7.51 Å, 8.48 Å, etc., which are consistent with Au-Au distances observed for a fcc Au system (for a simulated Au fcc PDF, see Fig. S5(a), ESI †).…”

“…23,53 What is rather crucial is the differences in structural behavior of these metal clusters, especially at relatively high temperatures when the complete deprotection 54 Moreover, we have previously shown via in situ HRTEM studies that deprotected metal clusters migrate on supports and then agglomerate to form bigger particles. 55 Fig. 3 presents the TEM images of as-prepared and thermally activated Ag clusters on alumina supports at different temperatures.…”

“…54 Moreover, we have previously shown via in situ HRTEM studies that deprotected metal clusters migrate on supports and then agglomerate to form bigger particles. 55…”

Thermodynamically and Kinetically Stabilized Pt Clusters Against Sintering on CeO2 Nanofibers Through Enclosing CeO2 Nanocubes

“…To dynamically understand the anti‐sintering mechanism, in situ electron microscopy is employed as a reliable observation tool for directly tracking the change of both metal and support in real‐time. [ 30 ] As shown in Figure A and Figure S8 (Supporting Information), the in situ heating experiment was conducted on Pt@ m ‐CeO 2 nanofibers. The corresponding HAADF‐STEM images were collected sequentially.…”

Following the temperature-induced activation of carbon-supported trigonal Pd3 nanoclusters for catalysis

“…[16][17][18] A major challenge during the thermal activation of NCs is temperature-driven sintering and/or oxidation of metal particles, which can also lead to changes in the catalytic behaviour of the catalyst. [19][20][21][22] Ostwald ripening and/or particle migration and coalescence are responsible for the sintering of the catalytic system, which causes size growth and deactivation of the catalytically active sites. 20 In the case of oxidation, surface oxidation may lead to passivation of the metal surface, and eventually deactivation of the catalyst.…”