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A series of well-defined M–N–C based SACs (M = Fe, Ni, Co, Mn and Cu) was synthesized via a facile pyrolysis of metal-doped ZIF-8 and applied in electrocatalytic CO2 reduction to CO. Fe–N–C based SACs possess highest activity for CO2RR.

The quantitative understanding of how atomic-level catalyst structural changes affect the reactivity of the electrochemical CO2 reduction reaction is challenging. Due to the complexity of catalytic systems, conventional in situ X-ray spectroscopy plays a limited role in tracing the underlying dynamic structural changes in catalysts active sites. Herein, operando high-energy resolution fluorescence-detected X-ray absorption spectroscopy was used to precisely identify the dynamic structural transformation of well-defined active sites of a representative model copper(II) phthalocyanine catalyst which is of guiding significance in studying single-atom catalysis system. Comprehensive X-ray spectroscopy analyses, including surface sensitive Δμ spectra which isolates the surface changes by subtracting the disturb of bulk base and X-ray absorption near-edge structure spectroscopy simulation, were used to discover that Cu species aggregated with increasing applied potential, which is responsible for the observed evolution of C2H4. The approach developed in this work, characterizing the active-site geometry and dynamic structural change, is a novel and powerful technique to elucidate complex catalytic mechanisms and is expected to contribute to the rational design of highly effective catalysts.

A well-defined Fe-based single-atom catalyst for electrocatalytic CO2 reduction to CO was synthesized via a facile pyrolysis of Fe-doped ZIF-8. Fe single-atomic sites exhibit optimum activity in producing CO with nearly 100% faradaic efficiency.

Polymorphism control of metal-organic frameworks is highly desired for elucidating structure-property relationships, but remains an empirical process and is usually done in a trial-and-error approach. We adopted the rarely used actinide cation Th4+ and a ditopic linker to construct a series of thorium-organic frameworks (TOFs) with a range of polymorphs. The extraordinary coordination versatility of Th4+ cations and clusters, coupled with synthetic modulation, gives five distinct phases, wherein the highest degree of interpenetration (threefold) and porosity (75.9 %) of TOFs have been achieved. Notably, the O atom on the capping site of the nine-coordinated Th4+ cation can function as a bridging unit to interconnect neighboring secondary building units (SBUs), affording topologies that are undocumented for other tetravalent-metal-containing MOFs. Furthermore, for the first time HCOOH has been demonstrated as a bridging unit of SBUs to further induce structural complexity. The resulting TOFs exhibit considerably different adsorption behaviors toward organic dyes, thus suggesting that TOFs represent an exceptional and promising platform for structure-property relationship study.

Molten salts have been reported to be excellent media for the preparation of multicationic oxides, which require harsh conditions to crystallize. Molten salt synthesis provides a wider operational temperature range (usually extends to 1000 °C) and faster mass transport and nucleation processes, thus allowing the preparation of crystalline solids, which require higher temperatures, such as perovskites. However, the mechanisms that control the solid-state formation and phase selection are poorly understood. Herein, several typical molten alkali metal halide (Cl−) and oxosalt (CO32− and SO42−) systems were employed as the reaction media for the synthesis of LaCoO3 (LCO) crystals, and the effects of ionic salt species on the morphological, geometric and electronic structures of LCO crystals were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray absorption spectroscopy (XAS). The LCO perovskite was successfully synthesized in a molten NaCl–KCl eutectic mixture at 700 °C, which was lower than that used for the conventional mixed oxide synthesis. Our results show that in the molten salt synthesis, the type of reaction medium, calcination temperature, the ratio of salt, and reaction time govern the microscopic mechanisms in the preparation of multicationic oxides. Most importantly, we observed that LaOCl was formed as an intermediate, which plays a key role in the reaction pathway for the phase-selective synthesis of perovskite LCO.

Development of efficient and affordable catalytic systems for direct H2O2 production from abundant resources is necessary to replace the current anthraquinone process and also to enable broader use...

Different sizes of layered CoOOH were synthesized by the molten-salt-assisted method at different temperatures. X-ray diffraction and scanning electron microscope studies reveal that CoOOH grew at (003) with increasing temperature, and its size can reach dozens of microns. X-ray absorption near edge structure and XPS studies demonstrate that the Co valence state of CoOOH-750 is trivalent, and X-ray Absorption Fine Structure shows that it had a higher symmetry and lower disorder degree, indicating that CoOOH-750 has higher crystallinity and Co3+. The results of electrochemical tests show that CoOOH-750 exhibited the best oxygen-evolution-reaction (OER) catalytic activity.

Development of a highly efficient and robust catalyst with reduced usage of noble metals is extremely desirable for selective hydrogenations of furan-containing bio-based feedstocks, which represents an attractive and sustainable alternative to petrochemical resources. Herein, we describe a new type of well-dispersed Ru subnanoclusters (ca. 0.50 wt%) supported on commercial P25 TiO2 material obtained from a facile and effective amino acid-assisted deposition–precipitation strategy. The as-synthesized catalyst exhibits superior catalytic activity and selectivity for direct hydrogenation of industrially important furfural as well as a range of structurally diverse bio-based furanic compounds to their corresponding fully hydrogenated derivatives. An average turnover frequency (ATOF) value as high as 367 h−1 at 80 °C and 4 MPa H2 is obtained, which is the highest reported value. This catalyst also shows stable furfural total hydrogenation in 5 reaction cycles conducted at 80 °C (52 mmol-scale, turnover number up to 12 500). In terms of the kinetic and structural characterizations, the key performances of the ultrasmall Ru clusters are proposed to mainly originate from an enhanced number of unsaturated surface Ru atoms and change in local coordination environment. Our work highlights the importance of the subnanometric size of Ru clusters in the advancement of efficient and affordable approaches towards bio-based chemical production.

Electrochemical CO2 reduction reaction (ECO2RR) is an important route for global carbon abatement. However, a comprehensive picture of the structure evolution of metal active sites is currently lacked in ECO2RR. Here, we present the first full view of Ni single-atom catalyst for ECO2RR over a broad potential range. Comprehensive X-ray absorption spectroscopy (XAS) analyses confirmed the Ni coordinated with pyrrole nitrogen in the form of Ni-N4 attached with an axial O2 ligand. Operando XAS revealed the precise structure of the Ni single-atom catalyst that dynamically changes with the shift of applied potentials. Such changes ultimately contributed to the CO selectivity variation ranging from 20%-99%. Interestingly, the Ni center was found to move toward the N4 plane during the ECO2RR, which played a crucial role of reaching near-unity CO selectivity. Together with theoretical calculations, a clear quantitative correlation between the dynamic configuration and the catalytic properties was established.

Constructing heterostructure is an important strategy to design efficient electrocatalysts. The synergetic interaction between dissimilar materials has been considered as the origin of the activity enhancement, however, the interfacial interaction is challenging to probe, thus, the underlying mechanism remains obscure. Here, we reported a heterostructured α-MoC/β-Mo2C electrocatalyst for hydrogen evolution in alkaline media, which shows a significant electrocatalytic activity improvement as compared to the single component. Based on extensive characterizations including high-resolution transmission electron microscopy and X-ray absorption fine structure (XAFS) spectroscopy, together with density functional theory, we unraveled the synergetic interaction between α-MoC and β-Mo2C, implying that α-MoC sites are beneficial for water dissociation and hydrogen prefers to release on β-Mo2C sites.

The development of function-integrated catalysts to enable scalable and efficient biomass valorization is an important topic. Here, a stepwise methodology was developed to fabricate novel supported Au–Pd bimetallic catalysts featuring immobilized well-defined on-surface nanoarchitectures (Pd∧Au). This was achieved by an atomic decoration of a trace amount of Pd (Pd/Au molar ratio of 0.01–0.02) on the surface of 2 nm Au nanoparticle (NP, 0.86 wt %) preanchored to titania. Benefiting from their unique structural merits and the cooperative interplay among the selective hydrogenation activity furnished by the ultrasmall Pd∧Au NPs and prominent Lewis acidity endowed by TiO2, Pd0.02∧Au/TiO2 exhibits excellent activity with 100% conversion and over 90% selectivity and stability (turnover number up to 48 300) toward controlled ring-opening conversion of 5-hydroxymethylfurfural and related furanic compounds to the corresponding di- and triketone-type products under mild conditions (120 °C, 10 bar of H2). The resul...

Cobalt carbide has recently been reported to catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins (C2–C4). Clarifying the formation process and atomic structure of cobalt carbide will help understand the catalytic mechanism of FTO. Herein, hydrogenation of carbon monoxide was investigated for cobalt carbide synthesized from CoMn catalyst, followed by X-ray diffraction, transmission electron microscopy, temperature programmed reaction and in situ X-ray absorption spectroscopy. By monitoring the evolution of cobalt carbide during syngas conversion, the wavelet transform results give evidence for the formation of the cobalt carbide and clearly demonstrate that the active site of catalysis was cobalt carbide.

Isolated cobalt single atoms with a high loading of 5.9 wt% are generated through an in situ preparation strategy., Single-atom catalysts (SACs) have shown great potential in a wide variety of chemical reactions and become the most active new frontier in catalysis due to the maximum efficiency of metal atom use. The key obstacle in preparing SAs lies in the development of appropriate supports that can avoid aggregation or sintering during synthetic procedures. As such, achieving high loadings of isolated SAs is nontrivial and challenging. Conventional methods usually afford the formation of SAs with extremely low loadings (less than 1.5 wt%). In this work, a new in situ preparation strategy that enables the synthesis of isolated cobalt (Co) SAs with an exceptionally high metal loading, up to 5.9 wt%, is developed. The approach is based on a simple one-step pyrolysis of a nitrogen-enriched molecular carbon precursor (1,4,5,8,9,12-hexaazatriphenylene hexacarbonitrile) and CoCl2. Furthermore, due to the successful electron transfer from carbon nitride to the isolated Co SAs, we demonstrate a high-performance photocatalytic H2 production using Co SAs as a co-catalyst, and the evolution rate is measured to be 1180 μmol g–1 h–1. We anticipate that this new study will inspire the discovery of more isolated SACs with high metal loadings, evidently advancing the development of this emerging type of advanced catalysts.

Hydrogenation of CO2 toward methane is a promising alternative for CO2 utilization and the development of highly efficient catalysts is the key factor for CO2 methanation. Herein, thin-layer SiOx matrix anchored nickel species catalysts (Ni/SiOx) with high specific surface area and a unique electronic/geometric structure have been successfully fabricated via a hydrothermal strategy. Ni3Si2O5(OH)4, with a typical layered structure and uniformly dispersed nickel sites, is an ideal precursor for Ni/SiOx catalysts for enhanced CO2 adsorption and chemical activation. The highly dispersed Ni active sites with suitable metal-support interactions with the SiOx matrix can promote CO2 conversion. Moreover, the pore structure and surface physicochemical properties of the Ni/SiOx samples can be tuned by changing the Ni/Si molar ratio. The optimized Ni/SiOx-2 catalyst shows outstanding catalytic efficiency with CO2 conversion of 64.2% and CH4 selectivity of 91.4% as well as excellent long-term (200 h) thermal stability for CO2 methanation under the conditions of 400 °C and the high gas hourly space velocity (GHSV) of 90 000 mL gcat−1 h−1. These findings can open new avenues towards the development of new-type nanomaterials in catalysis, especially renewable C1 chemistry transformations.

The route of converting CO2 to CO by reverse water-gas shift (RWGS) reaction is of particular interest due to the direct use of CO as feedstock in many significant industrial processes. Here, an engineered cobalt-cobalt oxide core-shell catalyst (Co@CoO) with nanochains structure has been made for the efficient reduction of CO2 to useful CO. Owing to the excellent performance for H2 activation of metal nanoparticles and the enhanced absorption and activation for CO2 molecule of defective metal oxides, the unique synergistic effect of metallic Co and encapsulating coordinatively unsaturated CoO species shows high performance for clean generation of CO under moderate and practical conditions. Furthermore, with N-dopant into the defective CoO shell, the Co@CoO-N achieves the highest conversion of 19.2 % and an exceptional CO evolution rate of 96 mL min-1 gcat-1 at 523 K with a gas hourly space velocity (GHSV) of 42,000 mL gcat-1 h-1 , which is comparable with the previously reported materials under identical conditions.

In-situ X-ray absorption fine structure spectroscopy (XAFS) has been widely used to study the structure around active site of catalysts at elevated pressures and temperatures for decades. However, methods of XAFS data analysis can vary significantly, depending on the disorder degree of the material system investigated. In this work, in-situ XAFS was explored to investigate the structural evolutions of the industry CuO/ZnO/Al2O3 catalyst for methanol synthesis at elevated temperatures in nitrogen (N2) atmosphere. Due to the large Debye–Waller factor, data analysis using the conventional Gaussian mode resulted in erroneously contracted Cu–Cu bond distances which made the conventional Gaussian mode invalid in this system. To account for the deviation from harmonic behavior, the cumulant expansion technique was used to correct the error in the bond contraction, and the frequency pattern could be fully reproduced by considering cumulants up to C3. In order to elucidate the contributions of the structure and thermal components to the Debye–Waller factors, the Einstein method was also used to analyze the data that provides a straightforward proof regarding the effect of the temperature on the in-situ XAFS experiment.

The chemical transformation of CO2 is an efficient approach in low-carbon energy system. The development of nonprecious metal catalysts with sufficient activity, selectivity, and stability for the generation of CO by CO2 reduction under mild conditions remains a major challenge. A hierarchical architecture catalyst composed of ultrathin graphene shells (2–4 layers) encapsulating homogeneous FeNi alloy nanoparticles shows enhance catalytic performance. Electron transfer from the encapsulated alloy can extend from the inner to the outer shell, resulting in an increased charge density on graphene. Nitrogen atom dopants can synergistically increase the electron density on the catalyst surface and modulate the adsorption capability for acidic CO2 molecules. The optimized FeNi3@NG (NG=N-doped graphene) catalyst, with significant electron penetration through the graphene layer, effects exceptional CO2 conversion of 20.2 % with a CO selectivity of nearly 100 %, as well as excellent thermal stability at 523 K.

The N-methylation of amines with CO2 and H2 is an important step in the synthesis of bioactive compounds and chemical intermediates. The first heterogeneous Au catalyst is reported for this methylation reaction with good to excellent yields. The average turnover frequency (TOF) based on surface Au atoms is 45 h(-1) , which is the highest TOF value ever reported for the methylation of aniline with CO2 and H2 . Furthermore, the catalyst is tolerant toward a variety of amines, which includes aromatic, aliphatic, secondary, and primary amines. Preliminary mechanistic studies suggest that the N-alkyl formamide might be an intermediate in the N-methylation of amine process. Moreover, through a one-pot process, it is possible to convert primary amines, aldehydes, and CO2 into unsymmetrical tertiary amines with H2 as a reductant in the presence of the Au catalyst.

Small gold nanoparticles (∼3 nm) loaded onto various supports have been prepared by a deposition–precipitation method and studied for direct methylation of N-methylaniline with CO2/H2. Among the catalysts examined, an acid–base bifunctional support γ-alumina supported gold catalyst (Au/γ-Al2O3) exhibits the best catalytic performance. Au/γ-Al2O3 catalysts with controlled mean Au particle sizes (1.8–8.3 nm) have also been successfully prepared by regulating the concentration of HAuCl4 in solution, aging time, aging temperature and mole ratio of urea to gold in the process of deposition–precipitation with urea. The turnover frequency (TOF) values for direct methylation of N-methylaniline with CO2/H2 increase on decreasing the mean size of Au nanoparticles (from 8.3 to 1.8 nm), showing that methylation of N-methylaniline with CO2/H2 is a structure-sensitive reaction. A fast increase in TOF occurs when the mean Au particle size becomes smaller than 3 nm. Through TEM (transmission electron microscope), gold L3-edge XAFS (X-ray absorption fine structure) and CO2- and NH3-TPD (temperature programmed desorption) analysis, we can conclude the Au particle sizes, oxidation state of the gold species and acid–base properties of the supports are responsible for the high catalytic activity of direct methylation of N-methylaniline with CO2/H2.

The production of methanol, an important fuel and chemical feedstock, from carbon dioxide is an important process for CO2 utilization. We describe herein a mild and efficient method for the indirect hydrogenation of carbon dioxide to methanol via a CO2-derived formate ester intermediate by using a simple heterogeneous catalyst system comprising Cu highly dispersed in an alumina matrix under solvent-free conditions. This catalyst is also effective for the hydrogenation of other formate esters, such as ethyl formate, propyl formate, and butyl formate.

In situ quick X-ray absorption spectroscopy (QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al2O3 catalyst for methanol synthesis. In this work, the catalyst, whose activity increases with the reaction temperature and pressure, was studied at calcined, reduced, and reacted conditions. TEM and EDX images for the calcined and reduced catalysts showed that copper was distributed uniformly at both conditions. TPR profile revealed two reduction peaks at 165 and 195 °C for copper species in the calcined catalyst. QXAFS results demonstrated that the calcined form consisted mainly of a mixed CuO and ZnO, and it was progressively transformed into Cu metal particles and dispersed ZnO species as the reduction treatment. It was demonstrated that activation of the catalyst precursor occurred via a Cu+ intermediate, and the active catalyst predominantly consisted of metallic Cu and ZnO even under higher pressures. Structure of the active catalyst did not change with the temperature or pressure, indicating that the role of the Zn was mainly to improve Cu dispersion. This indicates the potential of QXAFS method in studying the structure evolutions of catalysts in methanol synthesis.

Program of International ST Cooperation [2014DFG60230]; National Basic Research Program of China [2013CB933104]; National Natural Science Foundation of China [21303246, 11275258, 91127001]

The reductive methylation of cyclic amines (I) and (IV) as well as secondary amines (VI) with carbon dioxide proceeds readily in the presence of gold nanoparticles supported on γ-alumina as a heterogeneous catalyst.

Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H(2) from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118,400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H(2) evolution (TOFs up to 252 h(-1) after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO(2) interface.

One novel type of nanoscale cobalt–iron Prussian blue analogues (PBA) in the form of mixed nanorods and nanocubes were synthesized using cetyltrimethyl ammonium bromide (CTAB) as the surfactant in microemulsion at low temperature. The generated products were characterized by SQUID, XRD and IR techniques, etc. The effects of potassium contents, cobalt-to-iron ratios, reaction temperatures on the properties of the nanoscale cobalt–iron PBA were systematically explored. The results showed that the novel type of nanomaterials possessed distinct magnetic properties in that their coercivities were intensely dependent on cobalt-to-iron ratios and potassium contents. Furthermore, it was observed that low reaction temperature not only affected the morphologies of the products, but also had influence on their magnetic properties. Additionally, the cobalt–iron Prussian blue analogues were strongly influenced by CTAB around their surface, which led to higher Curie temperatures.

High temperature (HT) steam/CO2 coelectrolysis with solid oxide electrolysis cells (SOECs) using the electricity and heat generated from clean energies is an important alternative for syngas production without fossil fuel consumption and greenhouse gas emissions. Herein, reaction characteristics and the outlet syngas composition of HT steam/CO2 coelectrolysis under different operating conditions, including distinct inlet gas compositions and electrolysis current densities, are systematically studied at 800 °C using commercially available SOECs. The HT coelectrolysis process, which has comparable performance to HT steam electrolysis, is more active than the HT CO2 electrolysis process, indicating the important contribution of the reverse water-gas shift reaction in the formation of CO. The outlet syngas composition from HT steam/CO2 coelectrolysis is very sensitive to the operating conditions, indicating the feasibility of controlling the syngas composition by varying these conditions. Maximum steam and CO2 utilizations of 77% and 76% are achieved at 1.0 A cm−2 with an inlet gas composition of 20% H2/40% steam/40% CO2.

The formate-based rechargeable hydrogen battery (RHB) promises high reversible capacity to meet the need for safe, reliable, and sustainable H2 storage used in fuel cell applications. Described herein is an additive-free RHB which is based on repetitive cycles operated between aqueous formate dehydrogenation (discharging) and bicarbonate hydrogenation (charging). Key to this truly efficient and durable H2 handling system is the use of highly strained Pd nanoparticles anchored on graphite oxide nanosheets as a robust and efficient solid catalyst, which can facilitate both the discharging and charging processes in a reversible and highly facile manner. Up to six repeated discharging/charging cycles can be performed without noticeable degradation in the storage capacity.

Methanol is a sustainable source of liquid fuels and one of the most useful organic chemicals. To date, most of the work in this area has focused on the direct hydrogenation of CO2 to methanol. However, this process requires high operating temperatures (200-250 °C), which limits the theoretical yield of methanol. Thus, it is desirable to find a new strategy for the efficient conversion of CO2 to methanol at relatively low reaction temperatures. This Minireview seeks to outline the recent advances on the indirect hydrogenation of CO2 to methanol. Much emphasis is placed on discussing specific systems, including hydrogenation of CO2 derivatives (organic carbonates, carbamates, formates, cyclic carbonates, etc.) and cascade reactions, with the aim of critically highlighting both the achievements and remaining challenges associated with this field.

Syngas as a versatile hydrogen source: Using readily available and economically favorable syngas as a convenient hydrogen source, an efficient and sustainable aqueous reduction of bio-based carboxylic acids has been achieved over a highly robust catalyst system consisting of gold nanoparticles supported on acid-tolerant single-phase monoclinic zirconia (Au/m-ZrO(2)). A range of bio-based multifunctional carboxylic acids have been selectively converted into their corresponding lactones or diols in high to excellent yields.

The utilization of biomass has recently attracted tremendous attention as a potential alternative to petroleum for the production of liquid fuels and chemicals. We report an efficient alcohol-mediated reactive extraction strategy by which a hydrophobic mixture of butyl levulinate and formate esters, derived from cellulosic biomass, can be converted to valuable γ-valerolactone (GVL) by a simple supported gold catalyst system without need of an external hydrogen source. The essential role of the supported gold is to facilitate the rapid and selective decomposition of butyl formate to produce a hydrogen stream, which enables the highly effective reduction of butyl levulinate into GVL. This protocol simplifies the recovery and recycling of sulfuric acid, which is used for cellulose deconstruction.

Direct conversion of γ-valerolactone, which is one of the most significant cellulose-derived compounds, into 1,4-pentanediol was carried out by chemoselective hydrogenolysis catalyzed by a simple yet versatile copper–zirconia catalyst. Depending on the reaction conditions, 2-methyltetrahydrofuran could also be obtained in excellent yields.