In a groundbreaking study that introduces a fresh perspective on the design of single-atom catalysts (SACs), a research team led by Prof. LU Junling from the University of Science and Technology of China has successfully applied the Frontier Molecular Orbital (FMO) theory to enhance catalytic processes. Single-atom catalysis has emerged as a powerful tool in accelerating chemical reactions due to its unique structural advantages, including maximizing the utilization of noble metals while minimizing waste. Historically, SACs have demonstrated significant potential in various fields such as environmental remediation, energy conversion and storage, and fine chemical synthesis. However, the intricate mechanisms governing their activity and stability have remained elusive.
SACs consist of isolated metal atoms, such as palladium (Pd) or platinum (Pt), dispersed on a high-surface-area solid support. This configuration allows the active metal centers to interact effectively with reactants while the support influences the electronic properties of the metals. The fundamental challenge has been to elucidate how the interactions between the metal and the support, as well as between the metal and the adsorbates, dictate the overall performance of these catalysts. For instance, the metal–adsorbate interactions are known to significantly affect the activity of the SAC, while the metal–support interactions are critical to maintaining stability under reaction conditions.
Previous attempts to understand catalytic performance have often focused on either activity or stability in isolation, overlooking their interdependence. In their recent publication in Nature, the research team innovatively bridged this gap by applying the FMO theory, a conceptual framework previously used in molecular chemistry, to the realm of heterogeneous catalysis. This theoretical approach enabled them to derive relationships between electronic structures and catalytic performance, showcasing how tunable properties of the support can be exploited to optimize SACs.
The researchers constructed a series of 34 Pd1 SACs on distinct semiconductor oxide supports that varied in size and composition. To deepen their understanding of the electronic properties at play, the team meticulously measured the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) using advanced techniques like ultraviolet–visible (UV–Vis) spectroscopy and Mott–Schottky analysis. This effort allowed them to draw concrete correlations between the size of the supporting material and its influence on the electronic characteristics of the catalyst.
In a testament to their pioneering work, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) provided visual confirmation of the atomic dispersion of Pd on metal oxide supports. These imaging techniques, complemented by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS), confirmed enhanced electronic interactions between Pd and the metal oxide supports as the particle size decreased. Such interactions are crucial because they can significantly influence the reactivity of the catalyst and contribute to the stability of the SAC under operational conditions.
The practical implications of their findings were particularly evident in the semi-hydrogenation of acetylene. The study revealed that Pd1 SACs supported on nanoscale ZnO and CoOx exhibited an astonishing 20-fold increase in activity when compared to their bulk-oxide-supported counterparts. This significant performance boost coincided with the achievement of a remarkable turnover frequency (TOF) of 25.6 min–1 at a relatively moderate reaction temperature of 80 °C, marking a new benchmark for Pd1 SACs. Furthermore, this catalyst demonstrated stellar stability over a continuous 100-hour reaction period without any signs of coke formation or metal aggregation.
An essential aspect of the work was the correlation drawn between the catalyst’s intrinsic activities and the properties of Pd1 in the SACs. Interestingly, it was discovered that the activities of Pd1/MOx catalysts did not correlate directly with the charge states of Pd, which is a deviation from conventional wisdom. Instead, the activities manifested a linear scaling relationship with the LUMO positions of the n- and p-type oxide supports. This revelation underscores the influential role that the electronic structure of the supports plays in dictating the performance of SACs.
Delving deeper into the underlying mechanisms, the researchers employed theoretical calculations to dissect the interactions between metals and supports. They found that reducing the size of ZnO influences its LUMO level and widens the bandgap. This elevation in the LUMO of the support reduces the energy gap with the HOMO of Pd1 atoms, facilitating stronger orbital hybridization between Pd1 and the support. Such hybridization not only enhances stability but also strengthens the Pd1–adsorbate interactions, resulting in improved catalytic activity.
Ultimately, this research stands as a significant step forward in the quest for a unified theoretical framework that harmonizes the relationships between activity and stability in SACs. By providing direct experimental validation of the FMO theory in heterogeneous catalytic systems, the findings serve as a blueprint for future research and development of SACs. Importantly, the work also proposes a novel strategy for high-throughput screening of suitable metal-support combinations, harnessing the power of artificial intelligence to streamline and expedite the discovery of efficient catalytic systems.
This study invites a new era of design principles in catalyst engineering, favoring methodologies that prioritize a comprehensive understanding of electronic interactions at the atomic level. It propels the scientific community closer to the goal of developing catalysts that not only achieve high activity but also possess exceptional stability and durability, paving the way for advancements across various industrial processes.
As catalytic technologies continue to evolve in complexities and applications, this groundbreaking work highlights the crucial connections between theoretical insights and practical catalytic outcomes. The implications of these findings extend beyond the laboratory, offering transformative potential in fields ranging from renewable energy production to novel materials synthesis. It is a clear indication that the intersection of quantum chemistry and catalysis will play an increasingly pivotal role in addressing some of the world’s most pressing energy and environmental challenges.
Strong collaborations across institutions and disciplines will be essential as we seek to exploit the full potential of SACs, culminating in innovative designs that align with sustainable practices while driving technological progress in catalytic applications.
In conclusion, the integration of FMO theory within the study of single-atom catalysis marks a pivotal advancement in catalyst design and optimization, presenting new opportunities for research and technological innovation poised to reshape the landscape of chemical processes in the years to come.
Subject of Research: Single-atom catalysts (SACs) and their electronic interactions
Article Title: Metal–support frontier orbital interactions in single-atom catalysis
News Publication Date: April 2, 2025
Web References: Nature Article
References: DOI: 10.1038/s41586-025-08747-z
Image Credits: Credit: Image by Prof. LU et al.
Keywords
Single-atom catalysis, Frontier Molecular Orbital theory, Heterogeneous catalysis, Palladium catalysts, Semiconductor oxide supports, Catalytic activity, Electronic interactions, Stability, Hydrogenation reactions.
