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Single metal atoms supported on 2D carbon nitride are promising electrocatalysts for carbon dioxide reduction reaction.

International audience; Selective C-H functionalizations aiming at the formation of new C-N bonds is of paramount importance in the context of step-and atom-economy methodologies in organic synthesis. Although the implementation of noble metal catalysts is prevalent, more benign cobalt pre-catalysts have recently appeared promising. However, they sometimes feature selectivity issues that limits its applicability in late-stage functionalization. Herein, we report on a highly reactive ruthenium-based catalytic system displaying excellent levels of mono-, regio-and site-selectivity exploiting a series of biologically-relevant cyclic amides as weak directing groups. The use of dioxazolone derivatives as the amidating reagent overcomes the issues encountered in the use of unstable azide derivatives for such transformations and it enables to perform these reactions under very mild reaction conditions (air, 40 o C). Moreover, a combination of deuteration experiments and a comparative study with different types of directing groups highlight the relevance of weak amide directing groups for enabling formation of six-membered cycloruthenate intermediates in key elementary steps of the catalytic cycle. In addition, DFT computational calculations were carried out for the first time for studying ruthenium-catalyzed C-N bond-forming processes via C-H activation assisted by weak directing groups, thereby elucidating the origin of the regio-and site-selectivity.

International audience; Rhodium-catalysed hydroformylation, effective tool in bulk and fine-chemical synthesis, predominantly uses soluble metal complexes. For that reason, the metal leaching and the catalyst recycling are still the major drawbacks of this process. Single-atom catalysts have emerged as a powerful tool to combine the advantages of both homogeneous and heterogeneous catalysts. Since using an appropriate support material is key to create stable, finely dispersed, single-atom catalysts, here we show that Rh atoms anchored on graphitic carbon nitride are robust catalysts for the hydroformylation reaction of styrene.

The dichotomy between metal–organic frameworks (MOFs) and metal–organic cages (MOCs) opens up the research spectrum of two fields which, despite having similarities, both have their advantages and disadvantages. Due to the fact that they have cavities inside, they also have applicability in the porosity sector. Bloch and coworkers within this evolution from MOFs to MOCs manage to describe a MOC with a structure of Cu2 paddlewheel Cu4L4 (L = bis(pyrazolyl)methane) with high precision thanks to crystallographic analyses of X-ray diffraction and also SEM-EDX. Then, also at the same level of concreteness, they were able to find the self-assembly of Pd(II)Cl2 moieties on the available nitrogen donor atoms leading to a [Cu4(L(PdCl2))4] structure. Here, calculations of the DFT density functional allow us to reach an unusual precision given the magnitude and structural complexity, explaining how a pyrazole ring of each bis(pyprazolyl)methane ligand must rotate from an anti to a syn conformation, and a truncation of the MOC structure allows us to elucidate, in the absence of the MOC constraint and its packing in the crystal, that the rotation is almost barrierless, as well as also explain the relative stability of the different conformations, with the anti being the most stable conformation. Characterization calculations with Mayer bond orders (MBO) and noncovalent interaction (NCI) plots discern what is important in the interaction of this type of cage with PdCl2 moieties, also CuCl2 by analogy, as well as simple molecules of water, since the complex is stable in this solvent. However, the L ligand is proved to not have the ability to stabilize an H2O molecule.

Due to the important role of cocatalyst in the polymerization process employing industrially favored Ziegler–Natta catalysts, its effect on kinetic behavior, catalyst activity, and polymer properties is discussed. In this paper, triethyl aluminum (TEA) and triisobutyl aluminum (TIBA) have been used as the main cocatalyst ingredient with 10–20 mol percent of diethyl aluminum chloride (DEAC) and ethyl aluminum dichloride (EADC) cocatalysts, being neat TEA the cocatalysts with the highest activity. Moreover, TEA-DEAC and TEA-EADC cocatalysts revealed a built-up kinetic profile, while TIBA-DEAC and TIBA-EADC show a decay-type kinetic curve. According to melt flow index results, no considerable change in flowability was detected in the synthesized polyethylenes (PE). On the other hand, the ethylene insertion and chain termination mechanisms were investigated by means of density functional calculations using Ti active center located in (110) and (104) facets of the MgCl2 surface. To shed light on the bulkiness level of employed cocatalysts, buried volume (VBur) together with the two-dimensional map of cocatalyst systems were considered. Higher VBur of TIBA complex can explain its lower activity and decay type kinetic profile obtained by experimental studies Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. S.P.P thank the Spanish Ministerio de Ciencia e Innovacion for Juan de la Cierva Formacion fellowship (FJC2019-039623-I )

In the world of chemical catalysis and with the importance of being especially in the petrochemical industry, hydrogenation reactions play a central role. Within this framework, the hydrogenation of polyalphaolefins (PAOs) is receiving increasing attention. In this work, for the sake of efficiency and to furnish an efficient support for the immobilization of Pd nanoparticles, a new catalyst containing the 1,3-diaminopropane (DAP) diamine for the decoration of the halloysite (HNT) outer surface is used. The resulting catalytic system exhibited high activity in the hydrogenation of PAOs and high catalyst recyclability since it could be used for several reaction runs, with no appreciable loss of the catalytic activity and Pd leaching. In addition, the nature of the heterogeneous catalysis was demonstrated by a hot filtration test. Density functional theory (DFT) calculations not only unveil the reaction mechanism, in which the rate determining step was determined mechanistically, but also confirm the best location of the palladium nanoparticles, placed between the diamino ligands in the halloysite surface. Furthermore, the computational simulations rationalize why experimentally the catalytic process requires hydrogen pressure of 7 bar and temperature of 130°C to reach high yield Ministerio de Ciencia e Innovación, Grant/Award Numbers: PID2020-113711GB-I00, PGC2018-097722-B-I00; Iran Polymer and Petrochemical Institute, Grant/Award Number: 43794110; MCIN/AEI, Grant/Award Number: PID2021-127423NB-I00; Institució Catalana de Recerca i Estudis Avançats, Grant/Award Number: ICREA Academia 2019; Generalitat de Catalunya, Grant/Award Number: 2017SGR39 Open Access funding provided thanks to the CRUE-CSIC agreement with Wiley

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

The interaction between metal particles and the support in heterogeneous catalysis has been the subject of a large number of studies. While strong metal–support interactions can lead to deleterious...

Nonaqueous sodium-based batteries are ideal candidates for the next generation of electrochemical energy storage devices. However, despite the promising performance at ambient temperature, their low-temperature (e.g., < 0 °C) operation is detrimentally affected by the increase in the electrolyte resistance and solid electrolyte interphase (SEI) instability. Here, to circumvent these issues, we propose specific electrolyte formulations comprising linear and cyclic ether-based solvents and sodium trifluoromethanesulfonate salt that are thermally stable down to −150 °C and enable the formation of a stable SEI at low temperatures. When tested in the Na||Na coin cell configuration, the low-temperature electrolytes enable long-term cycling down to −80 °C. Via ex situ physicochemical (e.g., X-ray photoelectron spectroscopy, cryogenic transmission electron microscopy and atomic force microscopy) electrode measurements and density functional theory calculations, we investigate the mechanisms responsible for efficient low-temperature electrochemical performance. We also report the assembly and testing between −20 °C and −60 °C of full Na||Na3V2(PO4)3 coin cells. The cell tested at −40 °C shows an initial discharge capacity of 68 mAh g−1 with a capacity retention of approximately 94% after 100 cycles at 22 mA g−1.

The conversion of CO2 into methanol catalyzed by β-Mo2C and Cu/β-Mo2C surfaces has been investigated by means of a combined experimental and theoretical study. Experiments have shown the direct activation and dissociation of the CO2 molecule on bare β-Mo2C, whereas on Cu/β-Mo2C, CO2 must be assisted by hydrogen for its conversion. Methane and CO are the main products on the clean surface and methanol production is lower. However, the deposition of Cu clusters avoids methane formation and increases methanol production even above that corresponding to a model of the technical catalyst. DFT calculations on surface models of both possible C- and Mo-terminations, corroborate the experimental observations. Calculations for the clean Mo-terminated surface reveal the existence of two possible routes for methane production (C + 4H → CH4; CH3O + 3H → CH4 + H2O) which are competitive with methanol synthesis, displaying slightly lower energy barriers. On the other hand, a model for Cu deposited clusters on the Mo- terminated surface points towards a new route for methanol and CO production avoiding methane formation. The new route is a direct consequence of the generation of a Mo2C-Cu interface. The present experimental and theoretical results entail the interesting catalytic properties of Mo2C as an active support of metallic nanoparticles, and also illustrate how the deposition of a metal can drastically change the activity and selectivity of a carbide substrate for CO2 hydrogenation.

The water gas shift (WGS) reaction catalyzed by orthorhombic beta-Mo2C and cubic delta-MoC surfaces with and without Au clusters supported thereon has been studied by means of a combination of sophisticated experiments and state-of-the- art computational modeling. Experiments evidence the importance of the metal/carbon ratio on the performance of these systems, where Au/delta-MoC is presented as a suitable catalyst for WGS at low temperatures owing to its high activity, selectivity (only CO2 and H-2 are detected), and stability (oxycarbides are not observed). Periodic density functional theory-based calculations show that the supported Au clusters and the Au/delta-MoC interface do not take part directly in water dissociation but their presence is crucial to switch the reaction mechanism, drastically decreasing the effect of the reverse WGS reaction and favoring the WGS products desorption, thus leading to an increase in CO2 and H-2 production. The present results clearly display the importance of the Mo/C ratio and the synergy with the admetal clusters in tuning the activity and selectivity of the carbide substrate.

Based on periodic Density Functional Theory (DFT) calculations, carried out using a standard generalized gradient approximation type exchange-correlation functional including or not a van der Waals dispersive forces, the ability of the cubic δ-MoC(001) surface to capture methane at room temperature is suggested. Adsorption on the orthorhombic β-Mo2C(001) surfaces, with two possible terminations, has been also considered and, in each case, several molecular orientations have been tested with one, two, or three hydrogen atoms pointing towards the surface on all high-symmetry adsorption sites. The DFT results indicate that the δ-MoC(001) surface shows a better affinity towards CH4 than β-Mo2C(001). The calculated adsorption energy values on δ-MoC(001) surface are larger, and hence better, than on other methane capturing materials such as metal organic frameworks. Besides, the theoretical desorption temperature values estimated from the Redhead equation indicate that methane would desorbs at 330 K when adsorbed on the δ-MoC(001) surface, whereas this temperature is lower than 150 K when the adsorption involves β-Mo2C(001). Despite of this, adsorbed methane presents a very similar structure compared to the isolated molecule, due to a weak molecular interaction between the adsorbate and the surface. Therefore, the activation of methane molecule is not observed, so these surfaces are, in principle, not recommended as possible methane dry reforming catalysts.

CO2 hydrogenation to methanol and to other alcohols constitutes an appealing route to recycle the large amount accumulated in the atmosphere through fossil-derived fuels burning. However, CO2 high chemical stability makes the overall process difficult and appropriate catalysts are needed. Transition metal carbides, either as active phase or as a support for noble metal clusters, have been shown to be able to activate CO2. Here, the mechanism involved in the decomposition of H2 and CO2 on many early transition metal carbides (TMC) surfaces is analyzed with the help of density functional theory (DFT) based calculations complemented by key experiments. Results show that H2 dissociation on VC and δ-MoC is unlikely, that TiC and ZrC are more reactive leading to an exothermic but activated process and that the C:Mo ratio is determinant factor since H2 dissociation on β-Mo2C(001) surface is even more exothermic. The DFT based calculations also show that CO2 adsorption on TMC results in an activated species with TMC → CO2 charge transfer, C–O bond elongations and OCO bending. Supporting Cu4 and Au4 clusters on TMCs(001) surfaces leads to more active catalysts due to the induced charge polarization. For H2 dissociation, TiC appears to be the best support, enhancing both H2 thermodynamics and kinetics. CO2 is strongly adsorbed on supported Cu4 and Au4 clusters, and the adsorption energy strength correlates with the methanol formation rate: Cu4/TiC(001) > Au4/TiC(001) > Cu/ZnO(001) ≫ Cu(111), thus providing potential alternative catalysts for methanol synthesis, in principle dozens of times better than commercial Cu/ZnO based catalysts.

The adsorption and activation of a CO2 molecule on cubic δ-MoC(001) and orthorhombic β-Mo2C(001) surfaces have been investigated by means of periodic density functional theory based calculations using the Perdew–Burke–Ernzerhof exchange–correlation functional and explicitly accounting for (or neglecting) the dispersive force term description as proposed by Grimme. The DFT results indicate that an orthorhombic β-Mo2C(001) Mo-terminated polar surface provokes the spontaneous cleavage of a C–O bond in CO2 and carbon monoxide formation, whereas on a β-Mo2C(001) C-terminated polar surface or on a δ-MoC(001) nonpolar surface the CO2 molecule is activated yet the C–O bond prevails. Experimental tests showed that Mo-terminated β-Mo2C(001) easily adsorbs and decomposes the CO2 molecule. This surface is an active catalyst for the hydrogenation of CO2 to methanol and methane. Although MoC does not dissociate C–O bonds on its own, it binds CO2 better than transition metal surfaces and is an active and selective catalyst for the CO2 + 3H2 → CH3OH + H2O reaction. Our theoretical and experimental results illustrate the tremendous impact that the carbon/metal ratio has on the chemical and catalytic properties of molybdenum carbides. This ratio must be taken into consideration when designing catalysts for the activation and conversion of CO2.

The atomic structure and electronic properties of Cun nanoclusters (n = 4, 6, 7, and 10) supported on cubic nonpolar δ-MoC(001) and orthorhombic C- or Mo-terminated polar β-Mo2 C(001) surfaces have been investigated by means of periodic density functional theory based calculations. The electronic properties have been analyzed by means of the density of states, Bader charges, and electron localization function plots. The Cu nanoparticles supported on β-Mo2 C(001), either Mo- or C-terminated, tend to present a two-dimensional structure whereas a three-dimensional geometry is preferred when supported on δ-MoC(001), indicating that the Mo:C ratio and the surface polarity play a key role determining the structure of supported clusters. Nevertheless, calculations also reveal important differences between the C- and Mo-terminated β-Mo2 C(001) supports to the point that supported Cu particles exhibit different charge states, which opens a way to control the reactivity of these potential catalysts.

Molybdenum carbides are increasingly used in heterogeneously catalyzed hydrogenation reactions, which imply the adsorption and dissociation of molecular hydrogen. Here a systematic density functional theory based study, including or excluding dispersion terms, concerning the interaction and stability of H2 with cubic δ-MoC(001) and orthorhombic β-Mo2C(001) surfaces, is presented. In the latter case the two possible C or Mo terminations are considered. In addition, different situations for the H covered surfaces are examined. Computational results including dispersive forces predict an essentially spontaneous dissociation of H2 on β-Mo2C(001) independently of the surface termination, whereas on δ-MoC(001) molecular hydrogen dissociation implies a small but noticeable energy barrier. Furthermore, the ab initio thermodynamics formalism has been used to compare the stability of different H coverages. Finally, core level binding energies and vibrational frequencies are presented with the aim to assist the interpretation of yet unavailable data from X-ray photoelectron and infrared spectroscopies.

The ever growing increase of CO2 concentration in the atmosphere is one of the main causes of global warming. Thus, CO2 activation and conversion towards valuable added compounds is a major scientific challenge. A new set of Au/δ-MoC and Cu/δ-MoC catalysts exhibits high activity, selectivity, and stability for the reduction of CO2 to CO with some subsequent selective hydrogenation towards methanol. Sophisticated experiments under controlled conditions and calculations based on density functional theory have been used to study the unique behavior of these systems. A detailed comparison of the behavior of Au/β-Mo2C and Au/δ-MoC catalysts provides evidence of the impact of the metal/carbon ratio in the carbide on the performance of the catalysts. The present results show that this ratio governs the chemical behavior of the carbide and the properties of the admetal, up to the point of being able to switch the rate and mechanism of the process for CO2 conversion. A control of the metal/carbon ratio paves the road for an efficient reutilization of this environmental harmful greenhouse gas.