Abstract Nanosized palladium (Pd)-based catalysts are widely used in the direct hydrogen peroxide (H 2 O 2 ) synthesis from H 2 and O 2 , while its selectivity and yield remain inferior because of the O-O bond cleavage from both the reactant O 2 and the produced H 2 O 2 , which is assumed to have originated from various O 2 adsorption configurations on the Pd nanoparticles. Herein, single Pd atom catalyst with high activity and selectivity is reported. Density functional theory calculations certify that the O-O bond breaking is significantly inhibited on the single Pd atom and the O 2 is easier to be activated to form *OOH, which is a key intermediate for H 2 O 2 synthesis; in addition, H 2 O 2 degradation is shut down. Here, we show single Pd atom catalyst displays a remarkable H 2 O 2 yield of 115 mol/g Pd /h and H 2 O 2 selectivity higher than 99%; while the concentration of H 2 O 2 reaches 1.07 wt.% in a batch. 

/pdf/high-activity-and-selectivity-of-single-palladium-atom-for-1mxbvq9w.pdf

High activity and selectivity of single palladium atom for oxygen hydrogenation to H_2O_2

Single-atom catalytic sites may have existed in all supported transition metal catalysts since their first application. Yet, interest in the design of single-atom heterogeneous catalysts (SACs) only really grew when advances in transmission electron microscopy (TEM) permitted direct confirmation of metal site isolation. While atomic-resolution imaging remains a central characterization tool, poor statistical significance, reproducibility, and interoperability limit its scope for deriving robust characteristics about these frontier catalytic materials. Here, we introduce a customized deep-learning method for automated atom detection in image analysis, a rate-limiting step toward high-throughput TEM. Platinum atoms stabilized on a functionalized carbon support with a challenging irregular three-dimensional morphology serve as a practically relevant test system with promising scope in thermo- and electrochemical applications. The model detects over 20,000 atomic positions for the statistical analysis of important properties for establishing structure-performance relations over nanostructured catalysts, like the surface density, proximity, clustering extent, and dispersion uniformity of supported metal species. Good performance obtained on direct application of the model to an iron SAC based on carbon nitride demonstrates its generalizability for single-atom detection on carbon-related materials. The approach establishes a route to integrate artificial intelligence into routine TEM workflows. It accelerates image processing times by orders of magnitude and reduces human bias by providing an uncertainty analysis that is not readily quantifiable in manual atom identification, improving standardization and scalability.

/pdf/automated-image-analysis-for-single-atom-detection-in-1koldd3o.pdf

Automated Image Analysis for Single-Atom Detection in Catalytic Materials by Transmission Electron Microscopy.

Nanocrystals are of great importance in material sciences and industry. Engineering nanocrystals with desired structures and properties is no doubt one of the most important challenges in the field, which requires deep insight into atomic-scale dynamics of nanocrystals during the process. The rapid developments of in-situ transmission electron microscopy (TEM), especially environmental TEM have revealed insights into nanocrystals to digest. According to the considerable progress based on in-situ electron microscopy, we will give a comprehensive review on nanocrystal dynamics from three aspects: nucleation and growth, structure evolution, and dynamics in reaction conditions. In the nucleation and growth part, we organize existing nucleation theories and growth pathways based on liquid and gas-solid phases. In the structure evolution part, we focus on in-depth mechanistic understanding of the evolution, including defects, phase, and disorder/order transitions. In the part of dynamics in reaction conditions, we discuss solid-solid and gas-solid interfaces of nanocrystals in atmosphere and correlate the structure-property relationship. Even though impressive progress has been made, additional efforts are required to develop the integrated and operando TEM methodologies for unveiling nanocrystal dynamics with high spatial, energy, and temporal resolutions. This article is protected by copyright. All rights reserved.

Atomic-Scale Structure Dynamics of Nanocrystals Revealed by In-Situ and Environmental Transmission Electron Microscopy.

Single-atom heterogeneous catalysts for sustainable organic synthesis

Abstract Aiming at knowledge‐driven design of novel metal–ceria catalysts for automotive exhaust abatement, current efforts mostly pertain to the synthesis and understanding of well‐defined systems. In contrast, technical catalysts are often heterogeneous in their metal speciation. Here, we unveiled rich structural dynamics of a conventional impregnated Pd/CeO2 catalyst during CO oxidation. In situ X‐ray photoelectron spectroscopy and operando X‐ray absorption spectroscopy revealed the presence of metallic and oxidic Pd states during the reaction. Using transient operando infrared spectroscopy, we probed the nature and reactivity of the surface intermediates involved in CO oxidation. We found that while low‐temperature activity is associated with sub‐oxidized and interfacial Pd sites, the reaction at elevated temperatures involves metallic Pd. These results highlight the utility of the multi‐technique operando approach for establishing structure–activity relationships of technical catalysts.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/anie.202200434

Operando Spectroscopy Unveils the Catalytic Role of Different Palladium Oxidation States in CO Oxidation on Pd/CeO2 Catalysts

Atom dispersion in metal supported catalysts is vital as it structurally accounts for their catalytic performances. Since practical catalysts normally present structural diversity, such as the coexistence of single atoms, clusters, and particles, traditional spectroscopy methods including chemisorption, titration, and X-ray absorption, however, provide only an averaged description about the atom dispersion but are not able to distinguish localized structural divergence. In this work, through developing a methodology of electron-microscopy-based atom recognition statistics (EMARS), catalyst dispersion has been redefined at atomic precision in real space via the statistically counting 18 000+ Pt atoms for a Pt/Al2O3 industrial reforming catalyst. The EMARS results combined with in situ microscopy evidence disclose that the activity for aromatics production quantitatively correlates with the density of Pt single-atoms, while Pt clusters contribute no direct activity but could kinetically transform into single-atoms when being heated under an oxidative atmosphere. Compared to EMARS, the traditional hydrogen-oxygen titration method is found to induce serious bias in the Pt dispersion in reference to actual activity. This distinctive capability of EMARS for metal dispersion quantification offers a possibility of directly identifying the catalysis roles of different metal species in a practical catalyst via atom-resolved statistics.

Identify the Activity Origin of Pt Single-Atom Catalyst via Atom-by-Atom Counting.

Insights into the Active Sites of Al2O3-Supported NiMo Catalysts in the Hydrodenitrification Reaction

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Identify the Activity Origin of Pt Single-Atom Catalyst via Atom-by-Atom Counting.

Insights into the Active Sites of Al2O3-Supported NiMo Catalysts in the Hydrodenitrification Reaction