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Controlling the precise atomic architecture of supported metals is central to optimizing their catalytic performance, as recently exemplified for nanostructured platinum and ruthenium systems in acetylene hydrochlorination, a key process for vinyl chloride production. This opens the possibility of building on historically established activity correlations. In this study, we derived quantitative activity, selectivity and stability descriptors that account for the metal-dependent speciation and host effects observed in acetylene hydrochlorination. To achieve this, we generated a platform of Au, Pt, Ru, Ir, Rh and Pd single atoms and nanoparticles supported on different types of carbon and assessed their evolution during synthesis and under the relevant reaction conditions. Combining kinetic, transient and chemisorption analyses with modelling, we identified the acetylene adsorption energy as a speciation-sensitive activity descriptor, further determining catalyst selectivity with respect to coke formation. The stability of the different nanostructures is governed by the interplay between single atom–support interactions and chlorine affinity, promoting metal redispersion or agglomeration, respectively. ISSN:1748-3387 ISSN:1748-3395

Single-atom catalytic sites may have existed in all supported transition metal catalysts since their first application. Yet, interest in the design of single-atom heterogeneous catalysts (SACs) only really grew when advances in transmission electron microscopy (TEM) permitted direct confirmation of metal site isolation. While atomic-resolution imaging remains a central characterization tool, poor statistical significance, reproducibility, and interoperability limit its scope for deriving robust characteristics about these frontier catalytic materials. Here, we introduce a customized deep-learning method for automated atom detection in image analysis, a rate-limiting step toward high-throughput TEM. Platinum atoms stabilized on a functionalized carbon support with a challenging irregular three-dimensional morphology serve as a practically relevant test system with promising scope in thermo- and electrochemical applications. The model detects over 20,000 atomic positions for the statistical analysis of important properties for establishing structure–performance relations over nanostructured catalysts, like the surface density, proximity, clustering extent, and dispersion uniformity of supported metal species. Good performance obtained on direct application of the model to an iron SAC based on carbon nitride demonstrates its generalizability for single-atom detection on carbon-related materials. The approach establishes a route to integrate artificial intelligence into routine TEM workflows. It accelerates image processing times by orders of magnitude and reduces human bias by providing an uncertainty analysis that is not readily quantifiable in manual atom identification, improving standardization and scalability., Journal of the American Chemical Society, 144 (18), ISSN:0002-7863, ISSN:1520-5126

Activity equations trying to mimic experimental catalytic performance derived from reaction profiles and microkinetic models have been the state of the art in modeling in the last decades. This approach has been able to reproduce semiquantitatively activity volcano plots leading to successful catalyst optimization through the use of descriptors. As systems become more complex (both catalysts and reactants), these methods face increasing limitations. Statistical Learning (SL) techniques can overcome these limitations and improve the search for descriptor-based performance equations. However, the black-box nature of SL techniques makes physical interpretation of the so-obtained models difficult. To advance in the integration of these methodologies to real problems, we have merged experimental activity and selectivity presented as a function of chemical descriptors from Density Functional Theory for the catalyzed hydrodehalogenation of CH2X2 (for X = Br, Cl) leading to three main products. The employed Bayesian procedure is able to identify robust equations for activity and selectivity as a function of only two descriptors. This work provides a starting point to solve complex reaction networks using a set of statistical learning tools and hybrid data., ACS Catalysis, 12 (2), ISSN:2155-5435

The ability of Co3Mo3N to act as catalyst for the hydrogen evolution reaction at low overpotential is demonstrated. The identity of catalytic sites is established using DFT simulations.

Photoelectrochemistry has the potential to play a crucial role in the storage of solar energy and the realisation of a circular economy. From a chemical viewpoint, achieving high conversion efficiencies requires subtle control of the catalyst surface and its interaction with the electrolyte. Traditionally, such control has been hard to achieve in the complex multinary oxides used in PEC devices and consequently the mechanisms by which surface exposed facets influence light-driven catalysts are poorly understood. Yet, this understanding is critical to further improve conversion yields and fine-tune reaction selectivities. Here, we review the impact that crystal facets and disorder have on photoelectrochemical reactivity. In particular, we discuss how the crystal orientation influences the energetics of the surface, the existence of defects and the transport of reactive charges, ultimately dictating the PEC activity. Moreover, we evaluate how facet stability dictates the tendency of the solid to undergo reconstructions during catalytic processes and highlight the experimental and computational challenges that must be overcome to characterise the role of the exposed facets and disorder in catalytic performance.

CO2 electroreduction powered by renewable energy is an attractive strategy to close the carbon cycle. Among the possible reduction products, CO is of particular interest due to its large industrial applications. Transition metals in the Pt group are able to electrochemically reduce CO2 to CO, but suffer from CO surface poisoning, which causes a quick deactivation and overall sluggish kinetics. Here, we show that by introducing In to Pd-rich bimetallic particles we can tune the selectivity and limit the surface poisoning of these catalysts. The addition of large amounts of In blocks CO2 reduction activity and leads to a material selective for hydrogen evolution and insensitive to CO poisoning. This study provides insights into the dependence of CO2 reduction selectivity on the composition of Pd-In nanoparticles, revealing the effect that different phases have on catalytic activity. The application of similar screenings to other bimetallic systems can potentially yield cheap, selective, and poison-resistant catalysts for electrochemical applications.

Bimetallic single-atom catalysts (b-SACs) have recently gained prominence by virtue of the unique catalytic cooperative interactions they can exhibit, intertwining electronic and geometric effects. To date, research efforts have exclusively focused on direct mechanisms such as electron density transfer or sequential reactivity. Herein, the first study on indirect, coordination-induced catalytic synergies in carbon-supported Ru-Pt SACs is conducted. To this end, a holistic approach is developed, combining i) precision synthesis, ii) advanced characterization, iii) exploration of single-site adsorption properties via the hydrogen evolution reaction, and iv) modeling through density functional theory. Despite the lack of both intermetallic coordination in the first or second shell and charge redistribution effects, the Ru-Pt SACs exhibit a H-2 formation rate enhanced up to 15-fold compared with their monometallic counterparts. To unfold the origin of the intermetallic cooperativity, modifications of the structural and catalytic properties induced by the integration of a second metal species are investigated. Thus, Pt atoms are found to selectively occupy the most energeticallyfavorable cavities in the support, prompting Ru atoms to assume a distinct, more active, configuration. This contribution unveils a novel principle of bimetallic cooperativity, demonstrating the key role of integrative experimental and computational analyses in studying b-SACs., Advanced Functional Materials, 32 (52), ISSN:1616-3028, ISSN:1616-301X

Replying to: D. Le et al. Nature Catalysis https://doi.org/10.1038/s41929-022-00876-2 (2021)

Modeling of solid-state material-molecule interfaces in heterogeneous catalysis requires the extensive evaluation of the energy of molecules on surfaces. Obtaining the binding energy of many configurations of large organic molecules requires a vast amount of computational time with density functional theory (DFT). Here, we use a graph neural network (GNN) to evaluate the adsorption energy of molecular species adsorbed on metallic surfaces. The GNN is trained on a set of C1–4 fragments including N, O, S heteroatoms and C6–10 aromatic rings. Compared to DFT, the GNN shows a mean absolute error (MAE) of 0.17 eV on the test set being 6 orders of magnitude faster. When applying the trained model with subsequent hyperparameter optimization to molecules of industrial interest (biomass, plastics and polyurethanes precursors) containing up to 22 carbon atoms, the prediction performance for the adsorption energy yields a MAE of 0.03 eV/(non-H atom). While the error for out-of-distribution molecules is higher, it is still within the acceptable limit for adsorption energies (0.05 eV/atom), confirming the viability of the approach. The proposed framework represents a potential tool for the fast screening of catalytic materials, as well as their inverse design, enabling the multi-scale modeling for systems that cannot be easily simulated by DFT.

A robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology may hold the key to the practical utilization of these materials. An optimized chiral growth method to prepare fourfold twisted gold nanorods is described herein, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges are found to develop on the surface of single-crystal nanorods upon repeated reduction of HAuCl4, in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, it is proposed that the dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R-type and S-type chiral structures (small facets, terraces, or kinks) would thus be non-equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity.

The electrocatalytic reduction of carbon dioxide is widely studied for the sustainable production of fuels and chemicals. Metal ions in the electrolyte influence the reaction performance, although their main role is under discussion. Here we studied CO2 reduction on gold electrodes through cyclic voltammetry and showed that, without a metal cation, the reaction does not take place in a pure 1 mM H2SO4 electrolyte. We further investigated the CO2 reduction with and without metal cations in solution using scanning electrochemical microscopy in the surface-generation tip-collection mode with a platinum ultramicroelectrode as a CO and H2 sensor. CO is only produced on gold, silver or copper if a metal cation is added to the electrolyte. Density functional theory simulations confirmed that partially desolvated metal cations stabilize the CO2– intermediate via a short-range electrostatic interaction, which enables its reduction. Overall, our results redefine the reaction mechanism and provide definitive evidence that positively charged species from the electrolyte are key to stabilize the crucial reaction intermediate.

In this work, the effect of solar light as a “reducing agent” in Fe(VI)/PMS process for disinfection and decontamination of water was investigated. Single, double and triple-factor disinfection processes were systematically studied against Escherichia coli and validated on sulfamethoxazole. The experiments performed with PMS or Fe(VI) in dark conditions only achieved 1-log reduction in 2 h, while no significant enhancement was found in the Fe(VI)/PMS system. The introduction of solar light in either PMS or Fe(VI) process enhanced the E. coli inactivation, and complete inactivation (6-log) was reached at 90 min. However, the best improvement was achieved with the triple-factor disinfection process (Fe(VI)/PMS/solar light) which presented 6-log reduction at only 40 min. In the case of sulfamethoxazole, more than 70% removal was achieved under the Fe(VI)/PMS/solar light system, while only about 20% was observed with single and double-factor processes. Our study revealed the light spectrum distribution effects and the iron speciation implications. A main role for HO. and the participation of SO4.- was found, without overlooking the direct effects of solar light and PMS itself, as well as the possible involvement of other transient species. Overall, the efficacy of the Fe(VI)/PMS/solar light process against a series of microorganisms combined with the effectiveness at near-neutral pH, suggest its suitability for further assessment in disinfection and/or decontamination of water., Stefanos Giannakis would like to acknowledge the Spanish Ministry of Science, Innovation and Universities (MICIU) for the Ramón y Cajal Fellowship (RYC2018-024033-I) and the ‘NAVIA’ Project (PID2019-110441RB-C32). Núria López is grateful to the Spanish Ministry of Science and Innovation (aids for mobility for short-term research stays of FPU predoctoral staff, grant N° FPU-16/02101) which provided the economic support required to carry out the research stay at UPM.

Background: This work studied the use of the organic fertilizers DTPA-Fe and EDDS-Fe as iron chelates for solar driven photo-Fenton process at natural pH. This process was proposed to investigate its performance on removing a mixture of agrochemicals (propiconazole, imidacloprid and diuron) from pineapple processing wastewater to obtain a suitable effluent to be reused in the agricultural sector. Methods: Experiments were carried out in a solar simulator with a stirred cylindric photoreactor, with a volume of 150 mL and controlled temperature (20°C). The first set of experiments was carried out with ultrapure water to determine optimal iron and H2O2 concentrations. The second was performed with simulated wastewater of pineapple processing. Results: The optimized operational conditions for both iron complexes were 10 mg L-1 of Fe (III) and 25 mg L-1 of H2O2, since more than 80% of micropollutants (MP) (at an initial concentration of 1 mg L-1 of each compound) were removed in only 20 min with both DTPA-Fe and EDDS-Fe. The effect of organic matter and inorganic salts on radicals scavenging and chelates stability was also investigated in the experiments performed with synthetic pineapple processing wastewater. The results disclosed differences depending on the iron complex. Nitrites were the principal component influencing the tests carried out with EDDS-Fe. While carbonates at low concentration only significantly affected the experiments performed with DTPA-Fe, they were the major influence on the MPs removal efficiency decrease. In contrast, the presence of Ca2+ and Mg2+ only influence on this last one. Finally, the results of phytotoxicity disclosed the suitability of treated effluent to be reused in the agricultural sector. Conclusions: This work demonstrated that solar powered photo-Fenton catalysed by iron fertilizer EDDS is a suitable technology for depolluting water streams coming from pineapple processing plants at circumneutral pH, and its subsequent reuse for crop irrigation.

Electrochemical reduction of carbon dioxide (CO2RR) is an attractive route to close the carbon cycle and potentially turn CO2 into valuable chemicals and fuels. However, the highly selective generation of multicarbon products remains a challenge, suffering from poor mechanistic understanding. Herein, we used operando Raman spectroscopy to track the potential-dependent reduction of Cu2O nanocubes and the surface coverage of reaction intermediates. In particular, we discovered that the potential-dependent intensity ratio of the Cu–CO stretching band to the CO rotation band follows a volcano trend similar to the CO2RR Faradaic efficiency for multicarbon products. By combining operando spectroscopic insights with Density Functional Theory, we proved that this ratio is determined by the CO coverage and that a direct correlation exists between the potential-dependent CO coverage, the preferred C–C coupling configuration, and the selectivity to C2+ products. Thus, operando Raman spectroscopy can serve as an effective method to quantify the coverage of surface intermediates during an electrocatalytic reaction.

The development of CO2 electroreduction (CO2RR) catalysts based on covalent organic frameworks (COFs) is an emerging strategy to produce synthetic fuels. However, our understanding on catalytic mechanisms and structure-activity relationships for COFs is still limited but essential to the rational design of these catalysts. Herein, we report a newly devised CO2 reduction catalyst by loading single-atom centers, {fac-Mn(CO)(3)S}, (S = Br, CH3CN, H2O), within a bipyridylbased COF (COFbpyMn). COFbpyMn shows a low CO2RR onset potential (eta = 190 mV) and high current densities (>12 mA.cm(-2), at 550 mV overpotential) in water. TOFCO and TONCO values are as high as 1100 h-1 and 5800 (after 16 h), respectively, which are more than 10-fold higher than those obtained for the equivalent manganese-based molecular catalyst. Furthermore, we accessed key catalytic intermediates within a COF matrix by combining experimental and computational (DFT) techniques. The COF imposes mechanical constraints on the {fac-Mn(CO)(3)S} centers, offering a strategy to avoid forming the detrimental dimeric Mn-0-Mn-0, which is a resting state typically observed for the homologous molecular complex. The absence of dimeric species correlates to the catalytic enhancement. These findings can guide the rational development of isolated single-atom sites and the improvement of the catalytic performance of reticular materials.

This article investigates the activity of TiO2-rutile and TiO2-anatase polymorphs in the catalytic HBr oxidation, which is an enabling process to close the halogen loop in bromine-mediated transformation of natural gas to high-value chemicals and liquid fuels. The evaluation of rutile-, anatase-, and rutile-anatase TiO2 catalysts, exhibiting the variable specific surface areas, revealed that anatase phase is also active in this reaction. Nonetheless, in contrast to photocatalytic processes in which anatase is typically more active than rutile, rutile exhibits ca. 2–5 times higher intrinsic rates of HBr oxidation than anatase. Thereby, the apparent activation energies and reaction orders with respect to HBr, O2, and H2O display similar values for the two polymorphs. The activity differences were rationalized by density functional theory analysis, which showed that HBr oxidation follows a similar defect-driven mechanism over the most stable rutile (110) and anatase (101) surfaces. Herein, HBr activates the catalyst through a self-doping mechanism that involves the substitution of surface oxygen by bromine with the concomitant reduction of Ti4+ to Ti3+ centers. This forms a defect level that is placed in the band gap and allows for the O2 activation on the catalyst surface. While the HBr adsorption and H2O desorption display a similar energy profiles on both polymorphs, the O2 activation and Br2 evolution are more facile over rutile compared to anatase surface due to shorter distances between the coordinatively unsaturated Ticus sites and easier reduction of Ti4+ centers upon product desorption, respectively.

Dianionic hyponitrite (N2 O2 2- ) is often proposed, based on model complexes, as the key intermediate in reductive coupling of nitric oxide to nitrous oxide at the bimetallic active sites of heme-copper oxidases and nitric oxide reductases. In this work, we examine the gas-solid reaction of nitric oxide with the metal-organic framework CuI -ZrTpmC* with a suite of in situ spectroscopies and density functional theory simulations, and identify an unusual chelating N2 O2 .- intermediate. These results highlight the advantage provided by site-isolation in metal-organic frameworks (MOFs) for studying important reaction intermediates, and provide a mechanistic scenario compatible with the proposed one-electron couple in these enzymes.

Over the last decades, an increasing interest has been devoted to the generation of hydrogen from solar-powered water splitting devices as a direct approach to generate a clean and sustainable energy vector. Among the different alternatives, a direct photocatalytic process is the most straightforward, where a light absorber is able to produce hydrogen and oxygen under light irradiation without an external bias. Herein, we discuss the main pros and cons of photocatalytic water splitting for hydrogen production, aiming to offer a clear vision of the critical challenges that need to be overcome for these reactions to become a major player in the generation of solar fuels. The main parameters limiting solar-to-hydrogen yields and efficiencies, and the requirements for the descriptors of materials and components are introduced. We also describe the most promising semiconductors and material composites, highlighting their main features, along with future trends to improve photocatalytic stability, efficiency, and kinetics. Thus, our critical perspective grows from the state-of-the-art to focus on the future and viability of photocatalytic solar hydrogen.

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non-trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre-treatment of the ceria (CeO2 ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well-defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O22-) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on the powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites.

N-doped carbon (N-C) materials are increasingly popular in different electrochemical and catalytic applications. Due to the structural and stoichiometric diversity of these materials, however, the role of different functional moieties is still controversial. We have synthesized a set of N-C catalysts, with identical morphologies (∼27 nm pore size). By systematically changing the precursors, we have varied the amount and chemical nature of N-functions on the catalyst surface. The CO

The methoxycarbonylation of anilines stands as an attractive method for the phosgene-free production of carbamates. Despite the high yields obtained for ceria catalysts, the reduction of the amount of side products and the prevention of catalyst deactivation still represent major hurdles in this chemistry. One advantage of ceria is the possibility of tuning its reactivity by doping its lattice with other metals. In the present work, a series of doped ceria-based materials, prepared by substitution with metals, are evaluated in the methoxycarbonylation of 2,4-diaminotoluene with dimethyl carbonate. Among all catalysts, containing Eu, Hf, La, Pr, Sm, Tb, Y or Zr, ceria promoted with 2 mol % Zr exhibited 96 % selectivity towards the desired carbamates, improving the pure CeO2 catalyst. Density functional theory demonstrates that two descriptors are needed: 1) a geometric factor that governs the reduction of energy barriers for carbamate formation through ureas; 2) catalyst basicity as N-H bonds need to be activated. Assessment in subsequent reaction cycles revealed that the CeO2 -ZrO2 catalyst is more stable than bulk CeO2 , along with the reduction of fouling processes.

Copper catalysts are unique in CO2 reduction as they allow the formation of C2+ products. Depending on the catalysts’ synthesis, product distribution varies significantly: while Cu nanoparticles pr...

Polar surfaces of solid oxides are intrinsically unstable and tend to reconstruct due to the diverging electrostatic energy and thus often exhibit unique physical and chemical properties. However, a quantitative description of the restructuring mechanism of these polar surfaces remains challenging. Here we provide an atomic-level picture of the refaceting process that governs the surface polarity compensation of cubic ceria nanoparticles based on the accurate reference data acquired from the well-defined model systems. The combined results from advanced infrared spectroscopy, atomic-resolved transmission electron microscopy, and density functional theory calculations identify a two-step scenario where an initial O-terminated (2 × 2) reconstruction is followed by a severe refaceting via massive mass transport at elevated temperatures to yield {111}-dominated nanopyramids. This significant surface restructuring promotes the redox properties of ceria nanocubes, which account for the enhanced catalytic activity for CO oxidation.

We report the promoting effect of graphitic carbon nitride in Cu-catalyzed N-arylation. The abundance of pyridinic coordination sites in this host permits the adsorption of copper iodide from the r...

The Pourbaix diagram of Ni electrodes under reaction conditions presents several metastable NiOxHy phases and Fe doping enlarges the stability area of oxyhydroxo nature. For the Ni only phase water...

The catalyzed semi hydrogenation of dibromomethane (CH2Br2) to methyl bromide (CH3Br) is a key step in the bromine mediated upgrading of methane. This study presents a cutting edge strategy combini...

The worldwide replacement of the toxic mercuric chloride catalyst in vinyl chloride manufacture via acetylene hydrochlorination is slowed by the limited durability of alternative catalytic systems at high space velocities. Here, we demonstrate that platinum single atoms on carbon carriers are substantially more stable (up to 1,073 K) than their gold counterparts (up to 473 K), enabling facile and scalable preparation and precise tuning of their coordination environment by simple temperature control. By combining kinetic analysis, advanced characterization, and density functional theory, we assess how the Pt species determines the catalytic performance and thereby identify Pt(ii)−Cl as the active site, being three times more active than Pt nanoparticles. We show that Pt single atoms exhibit outstanding stability in acetylene hydrochlorination and surpass the space–time yields of their gold-based analogues after 25 h time-on-stream, qualifying them as a candidate for sustainable vinyl chloride production. Platinum nanoparticles have been neglected as a catalyst for acetylene hydrochlorination due to their limited activity. Here, the authors show that nanostructuring to the single-atom level renders platinum on carbonaceous supports a superior catalyst for this important industrial process.