Metal Sub-nanoclusters Confined within Hierarchical Porous Carbons with High Oxidation Activity

Unraveling the Unique Strong Metal-Support Interaction in Titanium Dioxide Supported Platinum Clusters for the Hydrogen Evolution Reaction

Strong metal-support interaction (SMSI) is crucial to modulating the nature of metal species, yet the SMSI behaviors of sub-nanometer metal clusters remain unknown due to the difficulties in constructing SMSI at cluster scale. Herein, we achieve the successful construction of the SMSI between Pt clusters and amorphous TiO2 nanosheets by vacuum annealing, which requires a relatively low temperature that avoids the aggregation of small clusters. In situ scanning transmission electron microscopy observation is employed to explore the SMSI behaviors, and the results reveal the dynamic rearrangement of Pt atoms upon annealing for the first time. The originally disordered Pt atoms become ordered as the crystallizing of the amorphous TiO2 support, forming an epitaxial interface between Pt and TiO2. Such a SMSI state can remain stable in oxidation environment even at 400 °C. Further investigations prove that the electron transfer from TiO2 to Pt occupies the Pt 5d orbitals, which is responsible for the disappeared CO adsorption ability of Pt/TiO2 after forming SMSI. This work not only opens a new avenue for constructing SMSI at cluster scale but also provides in-depth understanding on the unique SMSI behavior, which would stimulate the development of supported metal clusters for catalysis applications.

Carbon/copper oxide electrode materials with high atomic utilization constructed by in-situ induced growth strategy of nano metal-organic frameworks

Carbon/metal composites derived from metal-organic frameworks (MOFs) have attracted widespread attention due to their excellent electronic conductivity, adjustable porosity, and outstanding stability. However, traditional synthesis methods are limited by the dense stereo geometry and large crystal grain size of MOFs, resulting in many metals active sites are buried in the carbon matrix. While the common strategy involves incorporating additional dispersed media into material, this leads to a decrease in practical metal content. In this study, nanosized copper-metal-organic frameworks (Cu-MOFs) are in-situ grown on surface of carbon spheres by pre-anchoring copper ions, and the hybrid composite of porous carbon/copper oxide with high copper atom utilization rate is prepared through activation and pyrolysis methods. This strategy effectively addresses the issue of insufficient exposure of metal sites, and the obtained composite material exhibits high effective copper atom utilization rate, large specific surface area (2052.3 m2·g-1), diverse pore structure, outstanding specific capacity (1076.5F·g-1 at 0.5 A·g-1), and excellent cycle stability. Furthermore, this highly atom-economical universal method has positive significance in application fields of catalysis, energy storage, and adsorption.

Strong support effect induced by MXene for the synthesis of metal sulfides nanosheet arrays with sulfur vacancies towards selective CO2-to-CO photoreduction

Selective CO2-to-CO photoreduction is under intensive research and requires photocatalysts with tuned microstructures to accelerate the reaction kinetics. Here, we report CuInS2 nanosheet arrays with sulfur vacancies (VS) grown on the two-dimensional (2D) support of Ti3C2Tx MXene for CO2-to-CO photoreduction. Our results reveal that the use of Ti3C2Tx induces strong support effect, which causes the hierarchical nanosheet arrays growth of CuInS2 and simultaneously leads to charge transfer from CuInS2 to Ti3C2Tx support, resulting in VS formed in CuInS2. The strong support effect based on Ti3C2Tx is proven to be applicable to prepare a series of different metal indium sulfide arrays with VS. CuInS2 nanosheet arrays with VS supported on Ti3C2Tx benefit the photocatalytic selective reduction of CO2 to CO, manifesting a remarkable over 14.8-fold activity enhancement compared with pure CuInS2. The experimental and computational investigations pinpoint that VS of CuInS2 resulting from the support effect of Ti3C2Tx lowers the barrier of the rate-limiting step of *COOH → *OH + *CO, which is the key to the photoactivity enhancement. This work demonstrates MXene support effects and offers an effective approach to regulate the atomic microstructure of metal sulfides toward enhancing photocatalytic performance.

Mechanism and dynamics of Baeyer-Villiger oxidation of furfural to maleic anhydride in presence of H2O2 and Au clusters

CONTEXT

The increasing demand for fuels and chemicals in the world has prompted the exploration of various forms of renewable energy resources. Using C5-based furfural as the platform to replace the fossil energy resources is greatly attractive because of its abundance and environmental friendliness. Here we study the activity, selectivity, and possible reaction pathways for the Baeyer-Villiger oxidation of furfural over small Au clusters using hydrogen peroxide as oxidant. Furfural reacts with hydrogen peroxide in the presence of the catalysts with 93% selectivity towards maleic anhydride. Natural population analysis, frontier molecular orbital analysis, and spectroscopic analysis are used to illustrate the interaction mechanism between C5H4O2, H2O2, and Au. Reaction pathways leading to the formation of maleic anhydride are also explored. The reaction of C5H4O2 with H2O2 in the absence of a catalyst bears a relatively high transition state energy barrier of 2.98 eV for the first step involving absorption of H atom of H2O2 on the -OH group of C5H4O2. This is in agreement with the blank experiment where there were rare oxidation products observed in the absence of the metal cluster catalysts. On the other hand, transition state energies in the presence of the Au metal clusters are lower and the most feasible pathway is where the substrate and H2O2 co-bind on the Au catalyst and H2O2 molecule transfers an oxygen to the substrate, leading to the cleavage of the O-O bond.

METHODS

DFT calculations were done with B3PW91 functional. 6-311G(df, p) basis set was used for C, O, and H and aug-cc-pVDZ-PP was used for gold atoms. Gaussian 09 software was used for the calculations. Multiwfn 3.7 dev was used for the quantum theory of atoms-in-molecules (QTAIM) investigations.

Fluorination of Covalent Organic Framework Reinforcing the Confinement of Pd Nanoclusters Enhances Hydrogen Peroxide Photosynthesis

Metal-isolated clusters (MICs) physically confined on photoactive materials are of great interest in the field of photosynthesis of hydrogen peroxide (H2O2). Despite recent important endeavors, weak confinement of MICs in the reported photocatalytic systems leads to their low catalytic activity and stability. Herein, we report a new strategy of fluorinated covalent organic frameworks (COFs) to strongly confine Pd ICs for greatly boosting the photocatalytic activity and stability of H2O2 photosynthesis. Both experimental and theoretical results reveal that strong electronegative fluorine can increase the metal-support interaction and optimize the d-band center of Pd ICs, thus significantly enhancing the stability and activity of photocatalytic H2O2. An optimal TAPT-TFPA COFs@Pd ICs photocatalyst delivers a stable H2O2 yield rate of 2143 μmol h-1 g-1. Most importantly, the as-made TAPT-TFPA COFs@Pd ICs exhibit high catalytic stability over 100 h, which is the best among the reported materials.

Exploring the Potential Energy Surface of Pt6 Sub-Nano Clusters Deposited over Graphene

Catalytic systems based on sub-nanoclusters deposited over different supports are promising for very relevant chemical transformations such as many electrocatalytic processes as the ORR. These systems have been demonstrated to be very fluxional, as they are able to change shape and interconvert between each other either alone or in the presence of adsorbates. In addition, an accurate representation of their catalytic activity requires the consideration of ensemble effects and not a single structure alone. In this sense, a reliable theoretical methodology should assure an accurate and extensive exploration of the potential energy surface to include all the relevant structures and with correct relative energies. In this context, we applied DFT in conjunction with global optimization techniques to obtain and analyze the characteristics of the many local minima of Pt₆ sub-nanoclusters over a carbon-based support (graphene)-a system with electrocatalytic relevance. We also analyzed the magnetism and the charge transfer between the clusters and the support and paid special attention to the dependence of dispersion effects on the ensemble characteristics. We found that the ensembles computed with and without dispersion corrections are qualitatively similar, especially for the lowest-in-energy clusters, which we attribute to a (mainly) covalent binding to the surface. However, there are some significant variations in the relative stability of some clusters, which would significantly affect their population in the ensemble composition.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Subnanometric Cu clusters on atomically Fe-doped MoO2 for furfural upgrading to aviation biofuels

Single cluster catalysts (SCCs) are considered as versatile boosters in heterogeneous catalysis due to their modifiable single cluster sites and supports. In this work, we report subnanometric Cu clusters dispersed on Fe-doped MoO₂ support for biomass-derived furfural upgrading. Systematical characterizations suggest uniform Cu clusters (composing four Cu atoms in average) are homogeneously immobilized on the atomically Fe-doped ultrafine MoO₂ nanocrystals (Cu₄/Fe_0.3Mo_0.7O₂@C). The atomic doping of Fe into MoO₂ leads to significantly modified electronic structure and consequently charge redistribution inside the supported Cu clusters. The as-prepared Cu₄/Fe_0.3Mo_0.7O₂@C shows superior catalytic performance in the oxidative coupling of furfural with C₃~C₁₀ primary/secondary alcohols to produce C₈~C₁₅ aldehydes/ketones (aviation biofuel intermediates), outperforming the conventionally prepared counterparts. DFT calculations and control experiments are further carried out to interpret the structural and compositional merits of Cu₄/Fe_0.3Mo_0.7O₂@C in the oxidative coupling reaction, and elucidate the reaction pathway and related intermediates.

Highly porous nitrogen-doped carbon superstructures derived from the intramolecular cyclization-induced crystallization-driven self-assembly of poly(amic acid)

Hierarchically porous carbon nanomaterials have shown significant potential in electrochemical energy storage due to the promoted charge and mass transfer. Herein, a facile template-free method is proposed to prepare nitrogen-doped carbon superstructures (N-CSs) with multi-level pores by pyrolysis of polymeric precursors derived from the intramolecular cyclization-induced crystallization-driven self-assembly (ICI-CDSA) of poly(amic acid) (PAA). The excellent thermal stability of PAA enables the N-CSs to inherit the hierarchical structure of the precursors during pyrolysis, which facilitates the formation of meso- and macropores while the decomposition of the precursors promotes the creation of micropores. Electrochemical tests demonstrate the ultrahigh surface-area-normalized capacitance (76.5 μF cm-2) of the N-CSs facilitated by the hierarchically porous structure, promoting the charge and mass transfer, as well as the high utilization of pyridinic and pyrrolic nitrogen (12.9%) to provide significant pseudocapacitance contribution up to 40.6%. Considering the diversity of monomers of PAA, this ICI-CDSA strategy could be extended to prepare carbon nanomaterials with various morphologies, pore structures and chemical compositions.

CoP nanorods anchored on Ni2P-NiCoP nanosheets with abundant heterogeneous interfaces boosting the electrocatalytic oxidation of 5-hydroxymethyl-furfural

CoP nanorods anchored on Ni2P-NiCoP nanosheets have been fabricated. The heterogeneous interfaces can regulate the d-band centers of Co and Ni to approach the Fermi level, thus boosting the electrocatalytic oxidation of HMF.

Dual-Metal Hetero-Single-Atoms with Different Coordination for Efficient Synergistic Catalysis

Rationally tailoring the coordination environments of metal single atoms (SAs) is an effective approach to promote their catalytic performances, which, however, remains as a challenge to date. Here, we report a novel misplaced deposition strategy for the fabrication of differently coordinated dual-metal hetero-SAs. Systematic characterization results imply that the as-synthesized dual-metal hetero-SAs (exemplified by Cu and Co) are affixed to a hierarchical carbon support via Cu-C₄ and Co-N₄ coordination bonds. Density functional theory studies reveal that the strong synergistic interactions between the asymmetrically deployed CuC₄ and CoN₄ sites lead to remarkably polarized charge distributions, i.e., electron accumulation and deficiency around CuC₄ and CoN₄ sites, respectively. The obtained CuC₄/CoN₄@HC catalyst exhibits significantly enhanced capability in substrate adsorption and O₂ activation, achieving superior catalytic performances in the oxidative esterification of aromatic aldehydes in comparison with the Cu- and Co-based SA counterparts.

Recent advances in the conversion of furfural into bio-chemicals through chemo- and bio-catalysis

Furfural is a promising renewable platform molecule derived from hemi-cellulose, which can be further converted to fossil fuel alternatives and valuable chemicals due to its highly functionalized molecular structure. This mini-review summarizes the recent progress in the chemo-catalytic and/or bio-catalytic conversion of furfural into high-value-added chemicals, including furfurylamine, C₆ carboxylic acid, i.e., furandicarboxylic acid, furfural alcohol, aromatics, levulinic acid, maleic acid, succinic acid, furoic acid, and cyclopentanone, particularly the advances in the catalytic valorization of furfural into useful chemicals in the last few years. The possible reaction mechanisms for the conversion of furfural into bio-chemicals are summarized and discussed. The future prospective and challenges in the utilization of furfural through chemo- and bio-catalysis are also put forward for the further design and optimization of catalytic processes for the conversion of furfural.