Single-atom catalysts (SACs), characterized by exceptionally high atom efficiency, have garnered significant attention across various catalytic reactions. Recent studies have showcased SACs with robust capabilities for precise catalysis, specifically targeting reactions along designated pathways. This review focuses on the advances in the precise activation and reconstruction of chemical bonds on SACs, including precise activation of C–O and C–H bonds and selective couplings involving C–C and C–N bonds. Our discussion begins with a thorough exploration of the factors that render SACs skilled in precise catalytic processes, encompassing the narrow d-band electronic state of single atom site resulting in the adsorption tendency, isolate site resulting in unique adsorption structure, and synergy effect of a single atom site with its neighbors. Subsequently, we elaborate on the applications of SACs in electrocatalysis and thermocatalysis including four prominent reactions, namely, electrochemical CO2 reduction, urea electrochemical synthesis, CO2 hydrogenation, and CH4 activation. Then the concept of rational design of SACs for precisely controlling reaction pathways is discussed from the aspects of pore structure design, support-metal strong interaction, and support hydrophilic/hydrophobic. Finally, we summarize the challenges encountered by SACs in the field of precise catalytic processes and outline prospects for their further development in this domain.
The precise engineering of surface active sites is deemed as an efficient protocol for regulating surfaces and catalytic properties of catalysts. Defect engineering is the most feasible option to modulate the surface active sites of catalysts. Creating specific active sites on the catalyst allows precise modulation of its electronic structure and physicochemical characteristics. Here, we outlined the engineering of several types of defects, including vacancy defects, void defects, dopant-related defects, and defect-based single atomic sites. An overview of progress in fabricating structural defects on catalysts via de novo synthesis or post-synthetic modification was provided. Then, the applications of the well-designed defective catalysts in energy conversion and environmental remediation were carefully elucidated. Finally, current challenges in the precise construction of active defect sites on the catalyst and future perspectives for the development directions of precisely controlled synthesis of defective catalysts were also proposed.
As an important technology in fine chemical production, the selective hydrogenation of α,β-unsaturated aldehydes has attracted much attention in recent years. In the process of α,β-unsaturated aldehyde hydrogenation, a conjugated system is formed between >C=C< and >C=O, leading to hydrogenation at both ends of the conjugated system, which competes with each other and results in more complex products. Therefore, improving the reaction selectivity is also difficult in industrial fields. Recently, many researchers have reported that surface-active sites on catalysts play a crucial role in α,β-unsaturated aldehyde hydrogenation. This review attempts to summarize recent advances in understanding the effects of surface-active sites (SASs) over metal catalysts for enhancing the process of hydrogenation. The construction strategies and roles of SASs for hydrogenation catalysts are summarized. Particular attention has been given to the adsorption configuration and transformation mechanism of α,β-unsaturated aldehydes on catalysts, which contributes to understanding the relationship between SASs and hydrogenation activity. In addition, recent advances in metal-supported catalysts for the selective hydrogenation of α,β-unsaturated aldehydes to understand the role of SASs in hydrogenation are briefly reviewed. Finally, the opportunities and challenges will be highlighted for the future development of the precise construction of SASs.
Decalin is considered as an important compound of high-energy-density endothermic fuel, which is an ideal on-board coolant for thermal management of advanced aircraft. However, decalin contains two isomers with a tunable composition, and their effects on the pyrolysis performance, such as the heat sink and coking tendency have not been demonstrated. Herein, we investigated the pyrolysis of decalin isomers, i.e., cis-decalin, trans-decalin and their mixtures (denoted as mix-decalin), in order to clarify the effects of the cis-/trans-structures on the pyrolysis performance of decalin fuels. The pyrolysis results confirmed that conversion of the tested fuels (600–725 °C, 4 MPa) decreased in the order cis-decalin > mix-decalin > trans-decalin. Detailed analyses of the pyrolysis products were used to compare the product distributions from cis-decalin, mix-decalin and trans-decalin, and the yields of some typical components (such as cyclohexene, 1-methylcyclohexene, benzene and toluene) showed significant differences, which could be ascribed to deeper cracking of cis-decalin. Additionally, the heat sinks and coking tendencies of the decalins decreased in the order cis-decalin > mix-decalin > trans-decalin. This work demonstrates the relationship between the cis/trans structures and the pyrolysis performance of decalin, which provides a better understanding of the structure-activity relationships of endothermic hydrocarbon fuels.
