The Catalyst Review January 2025 - 14

Experimental Abstracts
Tailoring the Electronic Metal-Support Interactions in Supported Silver Catalysts
through AI modification for Efficient Ethylene Epoxidation
Metal-modified catalysts are commanding considerable attention
because of their enhanced geometric and electronic structures
and outstanding catalytic performances. Herein, the authors provide
an example of the effectiveness of such materials by making
use of the silver-catalyzed ethylene epoxidation as a case study.
Although silver (Ag) possesses the necessary active sites for conducting
this reaction, catalyst activity is usually sacrificed to obtain
high ethylene oxide (EO) selectivity. To overcome this challenge,
the authors developed an aluminum-modified manganese
dioxide-supported silver catalyst (Ag/Al-MnO2), which achieved
remarkable results: near-complete ethylene conversion
(approximately 100%) with 90% ethylene oxide selectivity
under mild conditions of 170°C and atmospheric pressure.
In addition to optimizing reaction conditions, these
workers
also employed structural characterization techniques and
DFT calculations to explain the behavior of their new catalyst.
The results of this investigation should assist in designing
advanced supported metal catalysts with high activity
and selectivity in heterogeneous selective oxidation reactions.
Figure 1. a) Schematic illustration of Ag/Al−MnO2 synthesis,
b,c) SEM images, d) HRTEM image and corresponding
energy-dispersive X-ray elemental.
mapping of Ag/Al−MnO2.
The authors prepared the Ag/Al-MnO2 catalyst using a systematic three-step procedure (Figure 1). Initially, they created the
aluminum-modified manganese dioxide support using a straightforward one-pot hydrothermal synthesis technique. Next,
they adsorbed silver precursors onto the support, and finally, they transformed the adsorbed silver diammine complex into
silver particles through a pyrolysis process. Experimental characterization of this catalyst showed that the Al modification
negligibly affected the geometric structure of Ag while changing its electronic properties. These electronic metal-support
interactions (EMSIs) can tailor the unoccupied 3d state of Ag, stabilize the Ag+ component, enhance the adsorption of ethylene
and oxygen to form an oxametallacycle (OMC) intermediate for EO production, and inhibit the C-Obond cleavage to
form acetaldehyde. As revealed by 'CANES and in situ XPS data, significantly more significant depletion occurred in the 3d
states of Ag in Ag/Al-MnO2 compared with those in Ag/MnO2, promoting significant activity and selectivity enhancement.
To better understand the origin of the enhanced catalytic performance for ethylene epoxidation resulting from the
introduction of Al into MnO2, density
functional
theory (DFT) calculations
were employed to investigate the
activation barriers for the formation of EO
using Ag/Al-MnO2 and Ag/MnO2 (Figure
2). The researchers discovered that the
electronic metal-support interactions modify
the silver catalyst's unoccupied 3d orbital,
facilitating rapid formation of the oxametallacycle
intermediate and reducing ethylene
oxide product adsorption. This modification
significantly enhances the ethylene oxide
formation rate, explaining
catalytic performance between the Ag/AlMnO2
and Ag/MnO2 catalysts. Yang H, Li G,
Liu Q, et al. (2024) Angew. Chem. Int. Ed., doi.
org/10.1002/anie.202400627
the distinct
Figure 2. a) The d orbital PDOS of Ag center for Ag/Al−MnO2 and Ag/MnO2
calculated by HSE06. b) Isostructural charge density difference plots of Ag/Al−
MnO2 and Ag/MnO2, yellow and cyan regions represent electron accumulation and
depletion, the isosurface is set to 0.004 e/Å³. Calculated free energy profiles for the
epoxidation of ethylene on c) Ag/Al−MnO2 and d) Ag/MnO2.
14
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The Catalyst Review January 2025

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