Operando X‐ray Powder Diffraction Study of Mechanochemical Activation Tested for the CO Oxidation over Au@Fe₂O₃as Model Reaction

Abstract

Mechanochemistry has proven to be an excellent green synthesis method for preparing organic, pharmaceutical, and inorganic materials. Mechanocatalysis, inducing a catalytic reaction by mechanical forces, is an emerging field because neither external temperature nor pressure inputs are required. Previous studies reported enhanced catalytic activity during the mechanical treatment of supported gold catalysts for CO oxidation. So far, the processes inside the milling vessel during mechanocatalysis could not be monitored. In this work, the results of high-energy operando X-ray powder diffraction experiments and online gas analysis will be reported. A specific milling setup with a custom-made vessel and gas dosing system was developed. To prove the feasibility of the experimental setup for operando diffraction studies during mechanocatalysis, the CO oxidation with Au@Fe 2 O 3 as a catalyst was selected as a well-known model reaction. The operando studies enabled monitoring morphology changes of the support as well as changes in the crystallite size of the gold catalyst. The change of the crystal size is directly correlated to changes in the active surface area and thus to the CO 2 yield. The studies confirm the successful implementation of the operando setup, and its potential to be applied to other catalytic reactions.

Solid-State Oxidation of Alcohols in Gold-Coated Milling Vessels via Direct Mechanocatalysis

“…[1,5,14,15] Both monometallic and bimetallic nanoparticles, particularly Au-Pd [4,5,16] on oxide supports, have been identified as exceptionally effective. [1,5,8,17] While gold-based catalysts are versatile in facilitating a range of oxidative [6,7,[18][19][20][21][22] and reductive [23,24] reactions, their application in both heterogeneous and homogeneous catalysis presents significant limitations. These include the need for high pressures or temperatures, which can negatively impact temperaturesensitive substrates, and the ongoing challenge of catalyst separation and recycling.…”

“…[34] Coating steel milling vessels with a robust, thin layer of gold, facilitated the reaction to run with soft polymer milling balls with no abrasion. Intriguingly, gold as a catalyst has seldom been employed in mechanochemistry, and where used, then only in nanoparticle form [19,20,24,36] . In this study, we introduce a pioneering approach to alcohol oxidation, employing elemental gold as a catalyst, uniquely applied as a coating on a milling tool.…”

Solid‐State Oxidation of Alcohols in Gold‐Coated Milling Vessels via Direct Mechanocatalysis

“…[1,5,14,15] Both monometallic and bimetallic nanoparticles, particularly Au-Pd [4,5,16] on oxide supports, have been identified as exceptionally effective. [1,5,8,17] While gold-based catalysts are versatile in facilitating a range of oxidative [6,7,[18][19][20][21][22] and reductive [23,24] reactions, their application in both heterogeneous and homogeneous catalysis presents significant limitations. These include the need for high pressures or temperatures, which can negatively impact temperature-sensitive substrates, and the ongoing challenge of catalyst separation and recycling.…”

“…Intriguingly, gold as a catalyst has seldom been employed in mechanochemistry, and where used, then only in nanoparticle form. [19,20,24,36] In this study, we introduce a pioneering approach to alcohol oxidation, employing elemental gold as a catalyst, uniquely applied as a coating on a milling tool. This innovation marks the first application of bulk gold as a direct mechanocatalyst, distinguished by its mild operating conditions and the catalyst's reusability (Figure 1).…”

Mechanocatalysis: Simple and Rapid Mechanochemical Synthesis of Ammonia in Hydrogen, Nitrogen, and Water System

“…[37] Chen et al proposed that a high-temperature process can be converted into an easily scalable solid-state synthesis by a low-temperature mechanochemical synthesis [(NiMgCuZnCo)O and Pt/Ru-(NiMgCuZnCo)O]. [25] The majority of mechanochemical transformations performed through ball milling techniques involve reactions of liquids and solids, but the quantity of mechanochemical reactions with gaseous products is increasing such as CH 4 , [38] CO, [31] CO 2 , [39][40][41] NH 3 , [1,14,15] and so forth.…”