Electrochemical water splitting in acid has been emerging as a powerful, sustainable and green protocol to produce hydrogen gas sources. In this study, we propose a novel strategy to fabricate RuO_x clusters anchored on self-assembled SnO₂ cubic nanocages (RuO_x-SnO₂ composites), which is substantiated by a combination of spectroscopy and microscopy. The resulting RuO_x-SnO₂ composite catalysts exhibit boosting oxygen evolution reaction (OER) performance: A Tafel slope of 41.2 mV·dec⁻¹ and a low overpotential of 225 mV@10 mA·cm⁻² in a 0.5 M H₂SO₄ (pH=0) electrolyte are achieved, outperforming the state-of-art OER catalyst of commercial RuO₂ (com-RuO₂). Notably, RuO_x-SnO₂ gives an extraordinarily large mass activity of 6873.4 A·g_Ru⁻¹ at the overpotential of 270 mV, which is approximately 170 times higher than that of com-RuO₂ (40.2 A·g_Ru⁻¹). The RuO_x-SnO₂ exhibits a good durability for at least 100 h@50 mA·cm⁻² and > 500 h@10 mA·cm⁻² and a stability of 30 hours at 100 mA·cm⁻² in an assembled proton exchange membrane water electrolysis, indicating that the engineered microstructure possesses significant potential for practical applications. The high intrinsic OER performance is attributed to the increasing density of exposed catalytic sites by downsizing RuO_x clusters with abundant oxygen vacancies (Ov, 1.02×10⁻¹² spin·mg_cat.⁻¹ determined by electron paramagnetic resonance). Furthermore, a Ru5c-Ov dual-active site mechanism is proposed by density functional theory calculations, that is, the moderate surface migration between five-coordinated surface Ru site (Ru5c) and Ov makes the *O→*OOH rate-determining step feasible. Moreover, this strategy provides a novel route for enhancing acidic OER activity and highly encouraging for their future applications of ruthenium-based composite catalysts.

Size hierarchy is a distinct feature of nanogold-catalysts as it can strongly affect their performance in various reactions. We developed a simple method to generate Au_nS_m nanoclusters of different sizes by thermal treatment of an Au₁₄₄(PET)₆₀ (PET: phenylethanethiol) parent cluster. These clusters, deposited on activated carbon, exhibit excellent catalytic performance in the hydrochlorination of acetylene. In-situ ultraviolet laser dissociation high-resolution mass spectrometry of the parent cluster in the presence of acetylene revealed a remarkable cluster size-dependence of acetylene adsorption, which is a crucial step in the hydrochlorination. Systematic density functional theory calculations of the reaction pathways on the differently-sized clusters provide deeper insight into the cluster size dependence of the adsorption energies of the reactants and afforded a scaling relationship between the adsorption energy of acetylene and the co-adsorption energies of the reactants (C₂H₂ and HCl), which could enable a qualitative prediction of the optimal Au_nS_m cluster for the hydrochlorination of acetylene.

The two-dimensional layered double hydroxides (LDHs) and zero-dimensional metal clusters have emerged as promising nanomaterials in the field of sustainable water oxidation, which can also facilitate joint experimental and computational studies. In this study, the synthesis of Ni₆@LDH composites, comprising atomically precise Ni₆(MPA)₁₂ (MPA: mercaptopropionic acid) clusters embedded into LDH nanosheets via electrostatic interaction, represents a significant advancement in the development of nanomaterials for sustainable water oxidation. Ni₆@NiFe-LDH exhibits superior electrochemical performance in oxygen evolution reaction (OER), exhibiting OER overpotentials of 198 mV@10 mA·cm⁻² and 290 mV@100 mA·cm⁻² with a low Tafel slope of 29 mV·dec⁻¹. It surpasses the corresponding NiFe-LDH and commercial RuO₂ catalysts, primarily due to the synergistic interaction between Ni₆ clusters and LDHs. Interestingly, our combined experimental and computational approach reveals that the M-OOH_ads formation is the rate-determining step (RDS) for the Ni₆-based catalysts, differing from the RDS for NiFe-LDH itself (the M-O_ads formation). These efforts serve as an attempt to push forward the current research frontier to study structure–property relationships progressing from the micro-/nano-level to the precise atomic-level.

Due to the powerful quantum confined space effects and multiple modes of small atomic sizes, metal nanoclusters (NCs) like thiolate-protected noble metals, such as silver (Ag) and gold (Au), which have a core sizes less than 3 nm, have developed a class of "metallic molecules" with multiple optical, magnetic, and electronic properties. To find a well-defined nanocatalysts, especially ligand-passivated metal NCs, great strides have been achieved in the efficient synthesis of atomically precise nanoparticles. Methods of synthesis such as bottom-up growth, top-down approach, ligand engineering, and interconversion system, are mentioned in this overview. Such clearly defined metal NCs have demonstrated considerable promise in catalysis research and have evolved into a distinct class of model catalysts. Focusing on the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER), this article attempts to outline current developments in NCs of molecular metals employed in electrocatalytic reactions. The paper highlights the relationship between the structure and performance of the catalytic mechanism and examines the potential effects of metal cluster sizes, metal core structures, charges, ligands, and metal–ligand binding patterns on their electrocatalytic activity. Future research opportunities and challenges are also proposed.

Heterojunction composites with intimate interfaces can shorten the diffusion distance, which leads to a shorter path for photogenerated carriers, thereby increasing photocatalytic activity. Herein, we report the fabrication of Ti₃C₂-Bi₂WO₆ (TC-BW) heterojunctions hinged by Bi₂Ti₂O₇ joints via an in situ hydrothermal reaction of Ti₃C₂ in the presence of Na₂WO₄ and Bi(NO₃)₃. The TC-BW was characterized using X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and Raman spectroscopy. TC-BW showed superior photocatalytic activity (productivity over 15TC-WB reaches up to 5.0 mmol_{reacted BA}·g_cat.⁻¹·h⁻¹) in the oxidation of benzyl alcohol using light-emitting diode (LED) light, arising from the surface defects and intimate heterojunction interface between the Ti₃C₂ MXene and Bi₂WO₆ nanosheets. TC-BW heterojunctions provide an enhanced separation efficiency of photogenerated charges, which in turn yields superior photocatalytic activity. Furthermore, it is well substantiated by density functional theory (DFT) calculations. In summary, this study elucidates the preparation of heterojunction composites with intimate interfaces for highly efficient photooxidation.

Catalysts for chemoselective hydrogenation are of vital importance for the synthesis of various important chemicals and intermediates. Herein we developed a simple method for preparing a highly efficient Ni-MoC_x nanocomposite catalyst via temperature-programmed carburization of a polyoxometalate precursor. X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) analyses indicate that the resulting mesoporous nanocomposite catalyst is made up of well-dispersed metallic nickel particles embedded in a MoC_x matrix. This catalyst exhibits high activity and selectivity (> 99%) in the hydrogenation of various substituted nitroaromatics to corresponding anilines. The high efficiency is attributed to the intimate contact of the constituents favoring electron transfer and hydrogen adsorption. Dihydrogen is physisorbed on the carbide support and dissociates on the nickel particles, as evidenced by Mo K-edge X-ray absorption near-edge structure (XANES) spectra, density functional theory (DFT), and hydrogen–deuterium exchange. The remarkable catalytic performance of the catalyst could be traced back to the synergistic interaction between the Ni particles and the carbide support. In-situ infrared spectroscopy and DFT simulations indicated that the adsorption/activation of the nitro group is favored compared to that of other substituents at the aromatic ring. In recyclability tests, the Ni-MoC_x nanocomposite showed no significant loss of catalytic performance in seven consecutive runs, indicating its robust nature.

Morphological effects of nanoparticles are crucial in many solid-catalyzed chemical transformations. We herein prepared two manganese-ceria solid solutions, well-defined MnCeO_x nanorods and MnCeO_x-nanocubes, exposing preferentially (111) and (100) facets of ceria, respectively. The incorporation of Mn dopant into ceria lattice strongly enhanced the catalytic performance in the NO reduction with CO. MnCeO_x (111) catalyst outperformed MnCeO_x (100) counterpart due to its higher population density of oxygen vacancy defects. In-situ infrared spectroscopy investigations indicated that the reaction pathway over MnCeO_x and pristine CeO₂ is similar and that besides the direct pathway, an indirect pathway via adsorbed hyponitrite as an intermediate cannot be ruled out. X-ray photoelectron and Raman spectroscopies as well as first-principles density functional theory (DFT) calculations indicate that the enhanced catalytic performance of MnCeO_x can be traced back to its “Mn–O_L(VÖ)–Mn–O_L(VÖ)–Ce” connectivities. The Mn dopant strongly facilitates the formation of surface oxygen vacancies (VÖ) by liberating surface lattice oxygen (O_L) via CO* + O_L → CO₂* + VÖ and promotes the reduction of NO, according to NO* + VÖ → N* + O_L and 2N* → N₂. The Mn dopant impact on both the adsorption of CO and activation of O_L reveals that a balance between these two effects is critical for facilitating all reaction steps.

Precise mono-doping of metal atom into metal particles at a specific particle position (e.g., the central site) in a highly controllable manner is still a challenge. In this work, we develop a highly controllable strategy for exchanging a single Ag atom into the central gold site of Au₁₃Ag₁₂(PPh₃)₁₀Cl₈ (Ph = phenyl) nanoclusters. Interestingly, a “pigeon-pair” cluster of {[Au₁₃Ag₁₂(PPh₃)₁₀Cl₈]·[Au₁₂Ag₁₃(PPh₃)₁₀Cl₈]}²⁺ is obtained and confirmed by electrospray ionization mass spectrometry (ESI-MS), thermogravimetric analysis (TGA) and single crystal X-ray diffraction (SCXRD) analysis. The experimental results and density functional theory (DFT) calculations suggest that the single-metal-atom exchanging from [Au₁₃Ag₁₂(PPh₃)₁₀Cl₈]⁺ to [Au₁₂Ag₁₃(PPh₃)₁₀Cl₈]⁺ occurs at the central position through the side entry of the μ₃-bridging Cl atoms. Finally, the effects on the electronic structure and properties caused by the single-atom exchange at the central site are shown by the enhancement of fluorescence and catalytic activity in the photocatalytic oxidation of ethanol.

We evaluated bismuth doped cerium oxide catalysts for the continuous synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide in the absence of a dehydrating agent. Bi_xCe_1-xO_δ nanocomposites of various compositions (x = 0.06-0.24) were coated on a ceramic honeycomb and their structural and catalytic properties were examined. The incorporation of Bi species into the CeO₂ lattice facilitated controlling of the surface population of oxygen vacancies, which is shown to play a crucial role in the mechanism of this reaction and is an important parameter for the design of ceria-based catalysts. The DMC production rate of the Bi_xCe_1-xO_δ catalysts was found to be strongly enhanced with increasing O_V concentration. The concentration of oxygen vacancies exhibited a maximum for Bi_0.12Ce_0.88O_δ, which afforded the highest DMC production rate. Long-term tests showed stable activity and selectivity of this catalyst over 45 h on-stream at 140 ℃ and a gas-hourly space velocity of 2,880 mL·g_cat^-1·h^-1. In-situ modulation excitation diffuse reflection Fourier transform infrared spectroscopy and first-principle calculations indicate that the DMC synthesis occurs through reaction of a bidentate carbonate intermediate with the activated methoxy (-OCH₃) species. The activation of CO₂ to form the bidentate carbonate intermediate on the oxygen vacancy sites is identified as highest energy barrier in the reaction pathway and thus is likely the rate-determining step.