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Abstract: Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the “complex active site” consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The “complex active site” Au−Vo−Zr3+ on Au1/ZrO2 exhibits the highest H2 production rate, with above 37,964 mol H2 per mol Au per hour (385 g H2  h−1) at 350 °C, which is 3.32, 2.94 and 15.0 times higher than Au1/CeO2, Au1/TiO2, and Au1/Al2O3, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost‐effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic‐level catalyst design by colocalizing catalytically active metal atoms forming a structure‐sensitive “complex site”, is a crucial way to advance from heterogeneous catalysis to molecular catalysis. Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

Developing atomically synergistic bifunctional catalysts relies on the creation of colocalized active atoms to facilitate distinct elementary steps in catalytic cycles. Herein, we show that the atomically-synergistic binuclear-site catalyst (ABC) consisting of [Formula: see text]-O-Cr6+ on zeolite SSZ-13 displays unique catalytic properties for iso-stoichiometric co-conversion of ethane and CO2. Ethylene selectivity and utilization of converted CO2 can reach 100 % and 99.0% under 500  °C at ethane conversion of 9.6%, respectively. In-situ/ex-situ spectroscopic studies and DFT calculations reveal atomic synergies between acidic Zn and redox Cr sites. [Formula: see text] ([Formula: see text]) sites facilitate β-C-H bond cleavage in ethane and the formation of Zn-Hδ- hydride, thereby the enhanced basicity promotes CO2 adsorption/activation and prevents ethane C-C bond scission. The redox Cr site accelerates CO2 dissociation by replenishing lattice oxygen and facilitates H2O formation/desorption. This study presents the advantages of the ABC concept, paving the way for the rational design of novel advanced catalysts.

Methane pyrolysis (MP) is a potential technology for CO2-free hydrogen production that generates only solid carbon by-products. However, developing a highly efficient catalyst for stable methane pyrolysis at a moderate temperature has been challenging. We present a new and highly efficient catalyst created by modifying a Ni-Bi liquid alloy with the addition of Mo to produce a ternary NiMo-Bi liquid alloy catalyst (LAC). This catalyst exhibited a considerably low activation energy of 81.2 kilojoules per mole, which enabled MP at temperatures between 450 and 800 Celsius and a hydrogen generation efficiency of 4.05 ml per gram of nickel per minute. At 800 Celsius, the catalyst exhibited 100% H2 selectivity and 120 hours of stability.

Nanoscale zerovalent iron (nZVI) is considered as a highly efficient material for sequestrating arsenite, but the origin of its high efficacy as well as the chemical transformations of arsenite during reaction is not well understood. Here, we report an in situ X-ray absorption spectroscopy (XAS) study to investigate the complex mechanism of nZVI reaction with arsenite under anaerobic conditions at the time scale from seconds to days. The time-resolved XAS analysis revealed a gradual oxidation of AsIII to AsV in the course of minutes to hours in both the solid and liquid phase for the high (above 0.5 g/L) nZVI dose system. When the reaction time increased up to 60 days, AsV became the dominant species. The quick-scanning extended X-ray absorption fine structure (QEAXFS) was introduced to discover the transient intermediate at the highly reactive stage, and a small red-shift in As K-edge absorption edge was observed. The QEAXFS combined with density functional theory (DFT) calculation suggested that the red-shift is likely due to the electron donation in a Fe-O-As complex and possible active sites of As sequestrations include Fe(OH)4 and 4-Fe cluster. This is the first time that the transient reaction intermediate was identified in the As-nZVI sequestration system at the fast-reacting early stage. This study also demonstrated usefulness of in situ monitoring techniques in environmental water research.

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour (579 mLH2 gRu-1 s-1) with 99.5% CO2 selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO2 selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

We demonstrate that the single-site catalyst Pt1/CeO2 greatly enhances the selectivity of cyclization and aromatization in the n-hexane reforming reaction. Specifically, the selectivity of single-site Pt1/CeO2 toward both cyclization and aromatization is above 86% at 350 °C. The turnover frequency of Pt1/CeO2 is 58.8 h-1 at 400 °C, which is close to that of Pt cluster/CeO2 (61.4 h-1) and much higher than that of Pt nanoparticle/CeO2 with Pt sizes of 2.5 and 7 nm. On the basis of the catalytic results for methylcyclopentane reforming, the dehydrocyclization and further aromatization of n-hexane are attributed to the prominent adsorption of ring intermediate products on the single-site Pt1/CeO2 catalysts. On the other side, with the multiple Pt adjacent active sites, the cluster and nanoparticle Pt/CeO2 samples favor the C-C bond cracking reaction. Ultimately, this in-depth study unravels the principles of hydrocarbon activation with different Pt sizes and represents a key step toward the rational design of new heterogeneous catalysts.

Herein, we present a scalable approach for the synthesis of a hydrogen-bonded organic-inorganic framework via coordination-driven supramolecular chemistry, for efficient remediation of trace heavy metal ions from water. In particular, using copper as our model ion of interest and inspired by nature's use of histidine residues within the active sites of various copper binding proteins, we design a framework featuring pendant imidazole rings and copper-chelating salicylaldoxime, known as zinc imidazole salicylaldoxime supramolecule. This material is water-stable and exhibits unprecedented adsorption kinetics, up to 50 times faster than state-of-the-art materials for selective copper ion capture from water. Furthermore, selective copper removal is achieved using this material in a pH range that was proven ineffective with previously reported metal-organic frameworks. Molecular dynamics simulations show that this supramolecule can reversibly breathe water through lattice expansion and contraction, and that water is initially transported into the lattice through hopping between hydrogen-bond sites.

Hydrogen is regarded as an attractive alternative energy carrier due to its high gravimetric energy density and only water production upon combustion. However, due to its low volumetric energy density, there are still some challenges in practical hydrogen storage and transportation. In the past decade, using chemical bonds of liquid organic molecules as hydrogen carriers to generate hydrogen in situ provided a feasible method to potentially solve this problem. Research efforts on liquid organic hydrogen carriers (LOHCs) seek practical carrier systems and advanced catalytic materials that have the potential to reduce costs, increase reaction rate, and provide a more efficient catalytic hydrogen generation/storage process. In this work, we used methanol as a hydrogen carrier to release hydrogen in situ with the single-site Pt1/CeO2 catalyst. Moreover, in this reaction, compared with traditional nanoparticle catalysts, the single site catalyst displays excellent hydrogen generation efficiency, 40 times higher than 2.5 nm Pt/CeO2 sample, and 800 times higher compared to 7.0 nm Pt/CeO2 sample. This in-depth study highlights the benefits of single-site catalysts and paves the way for further rational design of highly efficient catalysts for sustainable energy storage applications.

Electrochemical urea oxidation reaction (UOR) is a promising alternative to the oxygen evolution reaction for reducing the overall potential of the hydrogen evolution reaction during water electrolysis. The theoretical potential for the UOR is only 0.37 V versus reversible hydrogen electrode (RHE). However, the kinetics of the six-electron transfer process involved in the UOR are inherently sluggish, resulting in high overpotential during the reaction. This study designed an active catalyst with a lower kinetic barrier in the UOR by fabricating blending CoOOH–Ni(OH)2 nanoclusters through the structural transformation of amorphous Co–Ni hydroxide films. This structural transformation was investigated using high-angle annular dark-field scanning transmission electron microscopy, corresponding energy-dispersive X-ray spectroscopy, and in situ X-ray absorption spectra. The blending CoOOH–Ni(OH)2 nanoclusters exhibited superior electrocatalytic activity in the UOR in an alkaline environment, achieving a low onset potential of 1.24 V (vs. RHE) in 1 M KOH with 0.5 M urea. We employed the CoOOH–Ni(OH)2 nanoclusters as anodic electrocatalysts in a two-cell electrolyzer for asymmetric electrocatalysis. Hydrogen could be produced at a remarkable current density of 10 mA cm−2 at a low applied potential of only 0.45 V. Density functional theory calculations revealed that blending CoOOH–Ni(OH)2 nanoclusters with more oxygen vacancies exhibited a lower Gibbs free energy for the intermediate reaction pathway of NCONH2 → NCONH, compared with the fine structure of CoNiOx (x = 2–3). This study lays down a novel pathway for developing new blending electrocatalysts to be used in electrochemical reactions. [ABSTRACT FROM AUTHOR]

The Haber‐Bosch process is commonly used to produce ammonia while consuming energy and yielding huge emissions of carbon dioxide. Finding an alternative way to produce ammonia sustainably is a promising research direction with less CO2 emission. Photochemical nitrate reduction reaction (NtRR) to ammonia (NH3) could solve the nitrate pollutant problem in water and approach to produce ammonia with a more environmentally friendly process and lower energy consumption. In this work, the subnanometer‐sized copper oxide clusters decorated on titanium oxide nanoparticles (CuOx‐TiO2) were synthesized through the hydrothermal method and calcination treatment. CuOx‐TiO2 demonstrated impressively conversion rate of NO3− to NH3 with a yield of 153.09 μg‐gcat−1‐h−1 in KNO3 solution. The characteristic structure analysis revealed CuOx clusters with ~less than 1 nm decorated on TiO2 nanoparticles. From in‐situ X‐ray absorption fine structure (XAFS) spectroscopic technique, the transformation of the oxidation state of Cu clusters and the changes of local structure in the CuOx‐TiO2 were observed. The photocatalytic reaction mechanism of nitrate reduction on the CuOx‐TiO2 was successfully revealed. These discoveries have broad implications for the functional advancement of catalysts based on subnanometer‐sized clusters. Our findings may pave the way for exploring advanced ammonia synthesis routes with reduced energy consumption and carbon emissions. [ABSTRACT FROM AUTHOR]

The excessive energy demand of the conventional Haber–Bosch process for ammonia (NH3) generation, coupled with the disruptive effects of nitrate (NO3−) pollution on the global nitrogen cycle, has made the electrocatalytic nitrate reduction reaction (NO3−RR) an essential exit strategy for sustainable NH3 synthesis. However, the intricate multi-step proton and electron transfer process posed a great challenge in achieving high-efficiency electrocatalysts. In this study, we report a selective and highly active NO3−RR electrocatalyst featuring molecular M–Nx sites derived from the immobilization of Fe ions within N-doped graphene quantum dots (NGQDs). We demonstrated that the formation of molecular Fe–Nx coordination activated the NO3−RR of NGQDs-Fe, despite the initial inactivity of NGQDs. In situ Raman analysis revealed that those Fe–Nx sites served as favourable adsorption sites for *NO3. Such catalyst achieved an FE of 93% and a yield rate of 15.41 mmol h−1 cm−2 for NH3 at −0.8 V (vs. RHE) in an alkaline medium. These findings revealed the preferential sequential 2e− and 6e− transfer pathways over the direct 8e− pathway in the NO3−RR, which provides new mechanistic insights into the nitrate reduction reaction. [ABSTRACT FROM AUTHOR]