Rational construction of thermally stable single atom catalysts: From atomic structure to practical applications

Efficient catalytic oxidation of formaldehyde by defective g-C3N4-anchored single-atom Pt: A DFT study

Indoor volatile formaldehyde is a serious health hazard. The development of low-temperature and efficient nonhomogeneous oxidation catalysts is crucial for protecting human health and the environment but is also quite challenging. Single-atom catalysts (SACs) with active centers and coordination environments that are precisely tunable at the atomic level exhibit excellent catalytic activity in many catalytic fields. Among two-dimensional materials, the nonmagnetic monolayer material g-C3N4 may be a good platform for loading single atoms. In this study, the effect of nitrogen defect formation on the charge distribution of g-C3N4 is discussed in detail using density functional theory (DFT) calculations. The effect of nitrogen defects on the activated molecular oxygen of Pt/C3N4 was systematically revealed by DFT calculations in combination with molecular orbital theory. Two typical reaction mechanisms for the catalytic oxidation of formaldehyde were proposed based on the Eley-Rideal (E-R) mechanism. Pt/C3N4-V3N was more advantageous for path 1, as determined by the activation energy barrier of the rate-determining step and product desorption. Finally, the active centers and chemical structures of Pt/C3N4 and Pt/C3N4-V3N were verified to have good stability at 375 K by determination of the migration energy barriers and ab initio molecular dynamics simulations. Therefore, the formation of N defects can effectively anchor single-atom Pt and provide additional active sites, which in turn activate molecular oxygen to efficiently catalyze the oxidation of formaldehyde. This study provides a better understanding of the mechanism of formaldehyde oxidation by single-atom Pt catalysts and a new idea for the development of Pt as well as other metal-based single-atom oxidation catalysts.

Toward Functionality and Deactivation of Metal-Single-Atom in Heterogeneous Photocatalysts

Single-atom heterogeneous catalysts (SAHCs) provide an enticing platform for understanding catalyst structure-property-performance relationships. The 100% atom utilization and adjustable local coordination configurations make it easy to probe reaction mechanisms at the atomic level. However, the progressive deactivation of metal-single-atom (MSA) with high surface energy leads to frequent limitations on their commercial viability. This review focuses on the atomistic-sensitive reactivity and atomistic-progressive deactivation of MSA to provide a unifying framework for specific functionality and potential deactivation drivers of MSA, thereby bridging function, purpose-modification structure-performance insights with the atomistic-progressive deactivation for sustainable structure-property-performance accessibility. The dominant functionalization of atomically precise MSA acting on properties and reactivity encompassing precise photocatalytic reactions is first systematically explored. Afterward, a detailed analysis of various deactivation modes of MSA and strategies to enhance their durability is presented, providing valuable insights into the design of SAHCs with deactivation-resistant stability. Finally, the remaining challenges and future perspectives of SAHCs toward industrialization, anticipating shedding some light on the next stage of atom-economic chemical/energy transformations are presented.

Locally Ordered Single-Atom Catalysts for Electrocatalysis

Single-atom catalysts manifest nearly 100 % atom utilization efficiency, well-defined active sites, and high selectivity. However, their practical applications are hindered by a low atom loading density, uncontrollable location, and ambiguous interaction with the support, thereby posing challenges to maximizing their electrocatalytic performance. To address these limitations, the ability to arrange randomly dispersed single atoms into locally ordered single-atom catalysts (LO-SACs) substantially influences the electronic effect between reactive sites and the support, the synergistic interaction among neighboring single atoms, the bonding energy of intermediates with reactive sites and the complexity of the mechanism. As such, it dramatically promotes reaction kinetics, reduces the energy barrier of the reaction, improves the performance of the catalyst and simplifies the reaction mechanism. In this review, firstly, we introduce a variety of compelling characteristics of LO-SACs as electrocatalysts. Subsequently, the synthetic strategies, characterization methods and applications of LO-SACs in electrocatalysis are discussed. Finally, the future opportunities and challenges are elaborated to encourage further exploration in this rapidly evolving field.

Enhancing Oxygen Reduction on Fe Single-Atom Catalysts by Tuning Noncovalent Interactions in Electrode/Electrolyte Interfaces

Highly efficient electrochemical interfaces are significant for the oxygen reduction reaction (ORR). However, previous efforts have been mainly paid to design catalytic sites with high intrinsic activity and neglect the electrode/electrolyte interfaces, especially the noncovalent interactions in the outer Helmholtz plane (OHP). Herein, an Fe-N-C single-atom catalyst is synthesized and acts as the model catalyst to demonstrate the effect of noncovalent interactions on the ORR performance. Two specific molecules of THA+ and TEA+ with different structures and functional groups have been selected to tune the OHP through noncovalent interactions. TEA+ can adjust the OHP, improve the oxygen diffusion coefficient, and increase the double-layer capacitance. Therefore, TEA+ enhances the activity, selectivity, and stability of Fe-N-C single-atom catalysts toward the ORR. This provides a new approach to finding new directions in designing electrochemical interfaces beyond the intrinsic catalytic sites in acidic electrolytes.

Single-atom site catalysis in Li-S batteries

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

FePO4 supported Rh subnano clusters with dual active sites for efficient hydrogenation of quinoline under mild conditions

Chemoselective hydrogenation of quinoline and its derivatives under mild reaction conditions still remains a challenging topic, which requires a suitable interaction between reactants and a catalyst to achieve high performance and stability. Herein, FePO₄-supported Rh single atoms, subnano clusters and nanoparticle catalysts were synthesized and evaluated in the chemoselective hydrogenation of quinoline. The results show that the Rh subnano cluster catalyst with a size of ∼1 nm gives a specific reaction rate of 353 mol_quinoline mol_Rh^-1 h^-1 and a selectivity of >99% for 1,2,3,4-tetrahydroquinoline under mild conditions of 50 °C and 5 bar H₂, presenting better performance compared with the Rh single atoms and nanoparticle counterparts. Moreover, the Rh subnano cluster catalyst exhibits good stability and substrate universality for the hydrogenation of various functionalized quinolines. A series of characterization studies demonstrate that the acidic properties of the FePO₄ support favors the adsorption of quinoline while the Rh subnano clusters promote the dissociation of H₂ molecules, and then contribute to the enhanced hydrogenation performance. This work provides an important implication to design efficient Rh-based catalysts for chemoselective hydrogenation under mild conditions.

Metal-Organic Framework-Derived Atomically Dispersed Co-N-C Electrocatalyst for Efficient Oxygen Reduction Reaction

In this work, an atomically dispersed cobalt-nitrogen-carbon (Co-N-C) catalyst is prepared for the oxygen reduction reaction (ORR) by using a metal-organic framework (MOF) as a self-sacrifice template under high-temperature pyrolysis. Spherical aberration-corrected electron microscopy is employed to confirm the atomic dispersion of high-density Co atoms on the nitrogen-doped carbon scaffold. The X-ray photoelectron spectroscopy results verify the existence of Co-N-C active sites and their content changes with the Co content. The electrochemical results show that the electrocatalytic activity shows a volcano-shaped relationship, which increases with the Co content from 0 to 0.99 wt.% and then decreases when the presence of Co nanoparticles at 1.61 wt.%. The atomically dispersed Co-N-C catalyst with Co content of 0.99 wt.% shows an onset potential of 0.96 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.89 V vs. RHE toward ORR. The excellent ORR activity is attributed to the high density of the Co-N-C sites with high intrinsic activity and high specific surface area to expose more active sites.

Theoretical dissociation, ionization, and spin–orbit energetics of the diatomic platinum hydrides PtH, PtH+, and PtH–

Spin–orbit configuration interaction (SO-CI) and coupled-cluster [CCSDT(Q)] theoretical methods are combined to evaluate zero-temperature thermochemical properties of PtH, PtH+, and PtH−. We obtain vibrational zero-point energies and spin–orbit stabilization energies, which lead to predictions for observable quantities: ionization energy IE(PtH) = (9.44 ± 0.07) eV; electron affinity EA(PtH) = (1.65 ± 0.04) eV; and dissociation energies D0(Pt–H) = (329.6 ± 3.9) kJ mol−1, D0(Pt+–H) = (279.3 ± 5.7) kJ mol−1, and D0(Pt−–H) = (285.0 ± 2.4) kJ mol−1 (uncertainty coverage factor = 2). Compared with available experiments, our value of D0(Pt+–H) is higher by (8 ± 8) kJ mol−1, EA(PtH) is higher by 0.15 eV, and D0(Pt–H) is lower than the upper bound by (2 ± 4) kJ mol−1.

L-asparagine Assisted Synthesis of Pt/CeO2 Nanospheres for Toluene Combustion

Pt1/CeO2 nanospheres (Pt/CeO2-NS) were synthesized by the bath oiling method with L-asparagine as a necessary additive. Owing to the morphology control effect and coordination interaction of L-asparagine, CeO2 nanospheres can retain their nanosphere structure and show stronger electronic metal-support interaction with highly dispersed Pt. Moreover, the toluene catalytic combustion performance of Pt/CeO2-NS was investigated. The structure-performance relationship is analyzed according to the coordination state of Pt. The Pt/CeO2-NS catalyst exhibited superior catalytic activity than the commercial CeO2-supported Pt catalyst, which is attributed to its higher oxygen vacancy and Pt4+.