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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.

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.

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.

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.

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...

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...

CO2 electroreduction (CO2RR) is a sustainable alternative for producing fuels and chemicals. Metal cations in the electrolyte have a strong impact on the reaction, but mainly alkali species have been studied in detail. In this work, we elucidate how multivalent cations (Li+, Cs+, Be2+, Mg2+, Ca2+, Ba2+, Al3+, Nd3+, and Ce3+) affect CO2RR and the competing hydrogen evolution by studying these reactions on polycrystalline gold at pH = 3. We observe that cations have no effect on proton reduction at low overpotentials, but at alkaline surface pH acidic cations undergo hydrolysis, generating a second proton reduction regime. The activity and onset for the water reduction reaction correlate with cation acidity, with weakly hydrated trivalent species leading to the highest activity. Acidic cations only favor CO2RR at low overpotentials and in acidic media. At high overpotentials, the activity for CO increases in the order Ca2+ < Li+ < Ba2+ < Cs+. To favor this reaction there must be an interplay between cation stabilization of the *CO2– intermediate, cation accumulation at the outer Helmholtz plane (OHP), and activity for water reduction. Ab initio molecular dynamics simulations with explicit electric field show that nonacidic cations show lower repulsion at the interface, accumulating more at the OHP, thus triggering local promoting effects. Water dissociation kinetics is increasingly promoted by strongly acidic cations (Nd3+, Al3+), in agreement with experimental evidence. Cs+, Ba2+, and Nd3+ coordinate to adsorbed CO2 steadily; thus they enable *CO2– stabilization and barrierless protonation to COOH and further reduction products.

Truxene derivatives, due to their molecular structure and properties, are good candidates for the passivation of defects when deposited onto hybrid lead halide perovskite thin films. Moreover, their semiconductor characteristics can be tailored through the modification of their chemical structure, which allows-upon light irradiation- the interfacial charge transfer between the perovskite film and the truxene molecules. In this work, we analysed the use of the molecules as surface passivation agents and their use in complete functional solar cells. We observed that these molecules reduce the non-radiative carrier recombination dynamics in the perovskite thin film through the supramolecular complex formation between the Truxene molecule and the Pb2+ defects at the perovskite surface. Interestingly, this supramolecular complexation neither affect the carrier recombination kinetics nor the carriers collection but induced noticeable hysteresis on the photocurrent vs voltage curves of the solar cells under 1 sun illumination.

The use of chiral organic ligands during nanoparticle synthesis is key to designing optically active materials for biological and catalytic applications. To understand such complex processes at the...

The product distribution in direct alkane functionalization by oxyhalogenation strongly depends on the halogen of choice. We demonstrate that the superior selectivity to olefins over an iron phosphate catalyst in oxychlorination is the consequence of a surface‐confined reaction. By contrast, in oxybromination alkane activation follows a gas‐phase radical‐chain mechanism and yields a mixture of alkyl bromide, cracking, and combustion products. Surface‐coverage analysis of the catalyst and identification of gas‐phase radicals in operando mode are correlated to the catalytic performance by a multi‐technique approach, which combines kinetic studies with advanced characterization techniques such as prompt‐gamma activation analysis and photoelectron photoion coincidence spectroscopy. Rationalization of gas‐phase and surface contributions by density functional theory reveals that the molecular level effects of chlorine are pivotal in determining the stark selectivity differences. These results provide strategies for unraveling detailed mechanisms within complex reaction networks.

Electrocatalytic properties of materials are governed by the electronic structure, stability, and reactivity of the surface layer which is exposed to the electrolyte. Over the years, different strategies have been developed to tailor electrocatalyst surfaces but also to reduce the cost of these materials, which is the bottleneck for any practical application. When a very thin metallic layer, intended to serve as an electrocatalyst, is placed over a substrate, its configuration is influenced by the structure of the substrate due to lattice mismatch, while the electronic structure is affected due to the strain and the electronic effects of the support. This results in altered bonding within the electrocatalyst layer and the modification of its electronic properties when compared to the pure phase. In this contribution, we address the possibilities of theoretical prediction of surface properties of atomically thin electrocatalyst films formed over different substrates, focusing on the metal side of the elect...

The frontiers between homogeneous and heterogeneous catalysis are progressively disappearing. The decoration of transition metal nanoparticles (NPs) with ligands, also known as surface modifiers or capping agents, primarily allows NP size control but dramatically impacts activity and selectivity in catalysis. Computational tools have shown their capability of providing insight at atomic level in both homogeneous and heterogeneous areas but, due to the complexity of these interfaces, the underlying reaction mechanisms are often not described and certainly not well understood. In this mini-review, we describe the main challenges in modelling and survey the most recent computational studies that emphasise the role of ligands in tuning catalytic performance. We focus on density functional theory (DFT) simulations of the interfaces between transition metals (ruthenium, palladium, platinum, gold) and organic ligands (NHC, amine, phosphine, thiol), surfactants, and ionic liquids. Revealing the reaction pathways that operate at this hidden interface between homogeneous and heterogeneous worlds will provide guiding rules to design new systems that circumvent linear scaling relationships and foster a unified theory of catalysis.

Optimization of metal–support interactions (MSIs) is at the core of heterogeneous catalyst design. For polar reactants, electrostatic interactions resulting from MSIs can facilitate their activation. In this work, a feasible in situ method has been employed to control the electrostatic properties at the interface of a noble-metal-free Cu/Co(OH)2 nanohybrid catalyst. On the Cu/Co(OH)2 interface, the positively charged copper enhances the polar molecule adsorption. By varying the metal/support ratio, a highly efficient catalytic activity for the methanolysis of ammonia borane (AB) with an initial turnover frequency (TOF) of 61.63 mol(H2) mol(catalyst)−1 min−1 and long-term stability at ambient temperature were observed. Theoretical analysis unravels the role of charge transfer in promoting the reactions and the metal/support ratio in manipulating the catalytic activity via tuning electrostatic interactions.

The catalytic activity of membranes produced with commercial unmodified reduced graphene oxide (rGO) was demonstrated for the first time in persulfate (PS) activation through experiments performed in continuous mode. Phenol (Ph; C-0 = 5 mg L-1) and venlafaxine (VFX; C-0 = 250 mu g L-1) were employed as model compounds. The influence of the main operation parameters was first investigated considering an operation period of 24 h. For a rGO membrane with an effective area of 2.1 cm(2) , contaminant removal is favored at lower flow rates (0.1 mL min(-1)) and higher catalyst loads (15 mg). Assays carried out under these conditions yielded average removals of 90 and 94% for Ph and VFX, respectively, corresponding to normalized removal rates in the range of 1.71-1.79 L m(-2) h(-1) mg(cat)(-1). Membrane stability tests were conducted in continuous mode for 1 week, allowing to observe a significant catalyst deactivation after 2-3 d of operation, although the catalytic activity could be recovered through simple thermal regeneration procedures. Batch mode oxidation tests employing powder rGO treated at different temperatures (500, 850 and 1000 degrees C) and materials characterization data allowed to conclude that a shift of the surface chemistry character from acidic to basic enhances the catalytic performance. Moreover, scavenging tests indicated that singlet oxygen (O-1(2)), apparently generated by nucleophilic attack of PS to C = O in pyrone-like functionalities, is the main oxidizing species in the rGO-PS system.

Sustainable electrocatalysis of the oxygen evolution reaction (OER) constitutes a major challenge for the realization of green fuels. Oxides based on Ni and Fe in alkaline media have been proposed to avoid using critical raw materials. However, their ill-defined structures under OER conditions make the identification of key descriptors difficult. Here, we have studied Fe−Ni−Zn spinel oxides, with a well-defined crystal structure, as a platform to obtain general understanding on the key contributions. The OER reaches maximum performance when: (i) Zn is present in the Spinel structure, (ii) very dense, equimolar 1 : 1 : 1 stoichiometry sites appear on the surface as they allow the formation of oxygen vacancies where Zn favors pushing the electronic density that is pulled by the octahedral Fe and tetrahedral Ni redox pair lowering the overpotential. Our work proves cooperative electronic effects on surface active sites as key to design optimum OER electrocatalysts., This work was funded by the European Union under the H2020 FET-PROACT A-LEAF project (Grant Agreement No. 732840). The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by the Barcelona Supercomputing Center (QCM-2018-3-0012 Theoretical studies on catalysis optimization for an Artificial Leaf (A-LEAF)). ICN2 acknowledge funding from Generalitat de Catalunya 2017 SGR 327. ICN2 and UJI acknowledge funding from the Spanish MINECO coordinated project VALPEC (ENE2017-85087-C3). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme / Generalitat de Catalunya.

Five organic fertilizers (DTPA, EDDHA, HEDTA, EDTA and EDDS) were studied as iron sources for photo-Fenton process at natural pH to remove micropollutants (MPs) from wastewater for its reuse in irrigation. The results demonstrated that the stability constant of iron chelates is a key parameter for optimal micropollutants removal and it is linked to the structure of chelator. Mixtures of organic fertilizers were also tested to overcome excessive iron loose and to optimize MPs abatement kinetics. An improvement of photo-Fenton process occurred when using chelating mixtures. For instance, with 50 %EDDS + 50 %EDTA total removal of propranolol (PROP) was achieved at 30 min while EDTA needed up to 90 min of reaction and with EDDS total degradation was not achieved. In addition, the availability of dissolved iron of the mixture at the end of the treatment was 5.5 times higher than EDDS, increasing its suitability as reuse water for irrigation.

Metal promotion in heterogeneous catalysis requires nanoscale-precision architectures to attain maximized and durable benefits. Herein, we unravel the complex interplay between nanostructure and product selectivity of nickel-promoted In2O3 in CO2 hydrogenation to methanol through in-depth characterization, theoretical simulations, and kinetic analyses. Up to 10 wt.% nickel, InNi3 patches are formed on the oxide surface, which cannot activate CO2 but boost methanol production supplying neutral hydrogen species. Since protons and hydrides generated on In2O3 drive methanol synthesis rather than the reverse water-gas shift but radicals foster both reactions, nickel-lean catalysts featuring nanometric alloy layers provide a favorable balance between charged and neutral hydrogen species. For nickel contents >10 wt.%, extended InNi3 structures favor CO production and metallic nickel additionally present produces some methane. This study marks a step ahead towards green methanol synthesis and uncovers chemistry aspects of nickel that shall spark inspiration for other catalytic applications., Nature Communications, 12 (1), ISSN:2041-1723

The electroreduction of carbon dioxide using renewable electricity is an appealing strategy for the sustainable synthesis of chemicals and fuels. Extensive research has focused on the production of ethylene, ethanol and n‐propanol, but more complex C4 molecules have been scarcely reported. Herein, we report the first direct electroreduction of CO2 to 1‐butanol in alkaline electrolyte on Cu gas diffusion electrodes (Faradaic efficiency=0.056 %, j 1‐Butanol=−0.080 mA cm−2 at −0.48 V vs. RHE) and elucidate its formation mechanism. Electrolysis of possible molecular intermediates, coupled with density functional theory, led us to propose that CO2 first electroreduces to acetaldehyde‐a key C2 intermediate to 1‐butanol. Acetaldehyde then undergoes a base‐catalyzed aldol condensation to give crotonaldehyde via electrochemical promotion by the catalyst surface. Crotonaldehyde is subsequently electroreduced to butanal, and then to 1‐butanol. In a broad context, our results point to the relevance of coupling chemical and electrochemical processes for the synthesis of higher molecular weight products from CO2., Carbon dioxide was electroreduced to 1‐butanol on oxide‐derived copper. The reaction mechanism was determined to proceed through a combination of electrochemical and chemical steps, some of which require contrasting conditions. This example highlights limitations in one‐pot synthesis and provides a case for utilizing independently optimized sequential reactors in a tandem system to build complex molecules from low molecular‐weight feedstocks.

The growing generation of data and their wide availability has led to the development of tools to produce, analyze and store this information. Computational chemistry studies and especially catalytic applications often yield a vast amount of chemical information that can be analyzed and stored using these tools. In this manuscript we present a framework that automatically performs a full automated procedure consisting in the transfer of an adsorbate from a known metal slab to a new metal slab with similar packing. Our method generates the new geometry and also performs the required calculations and analysis to finally upload the processed data to an online database (ioChem-BD). Two different implementations have been built, one to relocate minimum energy point structures and the second to transfer transition states. Our framework shows good performance for the minimum point location and a decent performance for the transition state identification. Most of the failures occurred during the transition state searches needed additional steps to fully complete the process. Further improvements of our framework are required to increase the performance of both implementations. These results point to the _avoidhuman_ path as a feasible solution for studies on very large systems that require a significant amount of human resources and in consequence are prone to human errors.

In a water scarcity scenario, the reused wastewater could be an essential source for agricultural irrigation considering that 60% of fresh water is destined to this area. In this study, an organic fertilizer (Diethylene triamine pentaacetic acid, DTPA) was used as a new chelating agent of iron for photo-Fenton's application at neutral pH using LEDs. Secondary effluents with different characteristics were tested for propranolol removal and bacterial inactivation. With DTPA, the best results were achieved with MBR matrix: 94.0% of propranolol removal and total bacterial inactivation after 120 min. IFAS matrix showed the worst results: 63.2% of propranolol removal and only 2-log reduction for Total Coliforms. The performance of DTPA as chelating agent was compared with EDTA and EDDS with two matrices. In MBR matrix, propranolol removal with EDTA was 100% in 15 minutes, while DTPA and EDDS reached similar results at 120 minutes (94.0 and 91.3%), respectively. The iron precipitation was evaluated, and DTPA showed high stability with Fe2+ (only 10.4% of iron reduction instead 97.3% for EDDS). In addition, it looks like that the stability of iron chelates plays an important role in bacterial inactivation. Thus, the experiments with DTPA showed the lowest bacterial growth-on-the-plate after 72 hours of the end of the experiment. Biodegradability and phytotoxicity were also evaluated and the experiments with DTPA had the lowest toxicity. The results of the experiments performed with DTPA were compared with the values in Proposal for agricultural water reuse suggesting that treated effluent accomplish the requirements for agriculture.

The oxygen evolution reaction (OER) is the major bottleneck to develop viable and cost-effective water electrolysis, a key process in the production of renewable fuels. Hematite, all iron α-Fe2O3, would be an ideal OER catalyst in alkaline media due to its abundance and easy processing. Despite its promising theoretical potential, it has demonstrated very poor OER activity under multiple experimental conditions, significantly worse than that of Co or Ni-based oxides. In the search for improving hematite performance, we have analysed the effect of doping with redox vs. non-redox active species (Ni or Zn). Our results indicate that Zn doping clearly outperforms Ni, commonly accepted as a preferred dopant. Zn-doped hematite exhibits catalytic performances close to the state-of-the-art for alkaline water splitting: reaching 10 mA cm−2 at just 350 mV overpotential (η) at pH 13, thus twenty times that of hematite. Such a catalytic enhancement can be traced back to a dramatic change in the reaction pathway. Incorporation of Ni, as previously suggested, decreases the energetic barrier for the OER on the available centres. In contrast, Zn facilitates the appearance of a dominant and faster alternative via a two-site reaction, where the four electron oxidation reaction starts on Fe, but is completed on Zn after thermodynamically favoured proton coupled electron transfer between adjacent metal centres. This unique behaviour is prompted by the non-redox character of Zn centres, which maintain the same charge during OER. Our results open an alternative role for dopants on oxide surfaces and provide a powerful approach for catalytic optimisation of oxides, including but not limited to highly preferred all-iron oxides., The distinct beneficial effect of Zn-doping on the OER alkaline activity of Fe-based catalysts points towards an alternative and faster two-site mechanism.

Ceria has attracted considerable interest for the high-temperature electrocatalytic water splitting reaction (WSR) in solid oxide electrolysis cells (SOECs) due to the large active surface area enabled by its accessibility to ions, electrons and gas molecules. The mechanism of the WSR on the (1 1 1) facet of ceria has been studied extensively and hydroxyl decomposition is widely reported as the rate-determining step. However, WSR on other most-often exposed low-index surfaces like CeO2(1 1 0) and CeO2(1 0 0) remains unclear, especially the effect of high temperature on the formation of hydroxyls with different hydrogen coverage (ϴH) and reaction pathways. After identifying stable electron localization on cerium by using density functional theory corrected for on-site Coulomb interactions (DFT + U), we found that the formation of reaction intermediates such as oxygen vacancies, hydroxyls and vacancy-hydroxyl mixed phases on CeO2(1 0 0) is much more stable than that on CeO2(1 1 0) and CeO2(1 1 1). The higher stability of hydroxyls on CeO2(1 0 0) inhibits hydroxyl decomposition into H2, as compared to the reaction on the (1 1 0) and (1 1 1) facets, leading to the WSR on CeO2(1 1 0) and CeO2(1 1 1) 10 ~ 100 times faster than the reaction on CeO2(1 0 0) at temperature (T) < 950 K. In addition, we investigated the WSR via the formation of hydroxylated ceria with different coverage ϴH and found that the most efficient reaction pathway is also strongly facet-dependent, with the WSR on CeO2(1 0 0) and CeO2(1 1 1) preferentially proceeding on their overly hydroxylated surfaces (ϴH > 1, beyond one monolayer), while ϴH of the most active hydroxylated CeO2(1 1 0) decreased with the increase of temperature because of the unstable formation of highly hydroxylated CeO2(1 1 0) at high temperature. Our studies shed more light on the facet sensitivity of electrocatalysis on ceria.

The production of propylene from renewable resources might be relevant to provide this compound in a scenario of scarcity due to the use of shale gas as a raw material. In the present, work we provide a full density functional theory description of the reaction network that drives the hydrodeoxygenation of glycerol on molybdenum oxide. From these results, a microkinetic model is built that allows the analysis of the most common routes and the potential bottlenecks compromising the activity and selectivity of the process. With this integrated scheme, we have found that the reaction proceeds mainly through the formation of hydroxypropanal, propanal, and 1-propanol, and the reaction order for hydrogen is close to 1. Our work paves the way toward the evaluation of complex reaction networks for the study of biomass compounds.

Molybdenum oxides are finding increasing applications that rely on their redox character. For the most common polymorph, α-MoO3, oxygen vacancy formation leaves two electrons on the surface that can be stored as small polarons. Detailed density functional theory calculations that properly account for the self-interaction term, Ueff = 3.5 eV, show that the vacancy generates two different configurations: either two Mo5+ centers (Mo5+□ and Mo5+═O) or a single double-reduced Mo4+. These states are separated by 0.22 eV with a barrier for interconversion of 0.33 eV, and thus both are populated at catalytic temperatures, as shown by first-principles molecular dynamics. At higher reduction levels, vacancies can only be accumulated along a preferential direction and the energy difference between the 2×Mo5+ and Mo4+ configurations is reduced. These results point out the need for a revision of the experimental assignments based on our characterization that includes charges, vibrational frequencies, and XPS signatures.

The large-scale production of hydrogen from biomass under industrial conditions is fundamental for a sustainable future. Here we present a multiscale study of the available reforming technologies based on a density functional theory open database that allows the formulation of linear scaling relationships and microkinetics. The database fulfills the FAIR criteria: findability, accessibility, interoperability and reusability. Moreover, it contains more than 1000 transition states for the decomposition of C2 alcohols on close-packed Cu, Ru, Pd, and Pt surfaces. The microkinetic results for activity, selectivity toward H2, and stability can be directly mapped to experiments, and the catalytic performance is controlled by various types of poisoning. Linear scaling relationships provide valid quantitative results that allow the extrapolation to larger compounds like glycerol. Our database presents a robust roadmap to investigate the complexity of biomass transformations through the use of small fragments as surrogates when investigated under different reaction conditions. The production of hydrogen from biomass is of fundamental importance for a sustainable future. Here, the authors present a multiscale method that allows the formulation of scaling relationships and microkinetics of C1-C2 alcohol decomposition based on a density functional theory open database.

Increasing demand and high prices of advanced catalysts motivate a constant search for novel active materials with reduced content of noble metals. The development of thin films and core-shell catalysts seem to be a promising strategy along this path. Using Density Functional Theory we have analyzed a number of surface properties of supported bimetallic thin films with composition A3B (where A = Pt, Pd, B = Cu, Ag, Au). We focus on surface segregation, dissolution stability and surface electronic structure. We also address the chemisorption properties of Pd3Au thin films supported by different substrates, by probing the surface reactivity with CO. We find a strong influence of the support in the case of mono- and bilayers, while the surface strain seems to be the predominant factor in determining the surface properties of supported trilayers and thicker films. In particular, we show that the studied properties of the supported trilayers can be predicted from the lattice mismatch between the overlayer and the support. Namely, if the strain dependence of the corresponding quantities for pure strained surfaces is known, the properties of strained supported trilayers can be reliably estimated. The obtained results can be used in the design of novel catalysts and predictions of the surface properties of supported ultrathin catalyst layers., 23 pages, 5 figures, Supplementary Information included, submitted to Physical Chemistry Chemical Physics

Metal phosphides have emerged as a new powerful class of materials that can be employed as heterogeneous catalysts in transformations mainly to generate new energy vectors and the valorization of renewables. Synthetic protocols based on wet techniques are available and are based on the decomposition of the organic layer decorating the nanoparticles. For nickel, the phosphine of choice is trioctylphosphine, and this leads to the formation of NiPx materials. However, the temperature at which the decomposition starts has been found to depend on the quality of the nickel surface. Density functional theory, DFT, holds the key to analyze the initial steps of the formation of these phosphide materials. We have found how clean nickel surfaces, either (111) or (100), readily breaks the ligand P−C bonds. This triggers the process that leads to the replacement of a surface nickel atom by P and concomintantly forms a Ni adatom on the surface surrounded by two methyl groups, thus starting the formation of the NiPx phase. The whole process requires low energies, in agreement with the low temperature found in the experiments, 150 °C. In contrast, if the surface is oxidized, the reaction does not proceed at low temperatures and oxygen vacancies need to be created first to start the P−C bond breaking on the Ni-clean patches. Our results show that the cleaner the surface is, the milder the reactions are required for the NiPx formation, and thus they pave the way for gentler synthetic protocols that can improve the control of these materials.

The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H2 heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a cis isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H2 dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom–ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanis...

The shape control of nanoparticles constitutes one of the main challenges in today’s nanotechnology. The synthetic procedures are based on trial-and-error methods and are difficult to rationalize as many ingredients are typically used. For instance, concave nanoparticles exhibiting high-index facets can be obtained from Pt with different HCl treatments. These structures present exceptional capacities when are employed as catalysts in electrochemical processes, as they maximize the activity per mass unit of the expensive material. Here we show how atomistic simulations based on density functional theory that take into account the environment can predict the morphology for the nanostructures and how it is even possible to address the appearance of concave structures. To describe the control by etching, we have reformulated the Wulff construction through the use of a geometric model that leads to concave polyhedra, which have a larger surface-to-volume ratio compared to that for nanocubes. Such an increase makes these sorts of nanoparticles excellent candidates to improve electrocatalytic performance

Journal of Materials Chemistry A, 5 (31), ISSN:2050-7488, ISSN:2050-7496

Single atom heterogeneous catalysts, SAHCs, have been considered as one of the holy grails in catalysis as they enable the best utilization of scarce and expensive catalytic noble metals. Obtaining atomic dispersions in a matrix is relatively easy but the thermodynamics favour the formation of nanoparticles, as roughly saying, the cohesive energy per atom is gained by agglomeration. The nature of SAHC interactions with the matrix is crucial as it controls the electronic structure of the atom, its charge, the coordination pattern (that might be different from a solid) and the overall catalytic ensemble. In order to avoid coalescence, SAHC interactions with the carrier should be strong enough that the electron clouds of catalytically active atoms are compromised in bonds with the host lattice and that they are made catalytically inert as no additional bonds can be formed. The dispersion of single catalytic atoms is controlled by the relative bond strength between the metal and the matrix, the metals' own cohesive energy and the topology of the active adsorption sites available in the matrix. As a consequence, a few classes of hosts including metals, oxides, carbon nitrides, molecular crystals and metal organic frameworks allow the efficient formation of SAHCs. So far, these matrixes have been examined independently and thus a common framework to study these SAHCs has not been proposed. Theoretical tools hold the key to investigate the properties of the potentially catalytic metals transversally (in different carriers), which is precisely the aim of the present work. We have checked all these aspects by studying the same single atom, Pt in oxides, metals and carbon nitride. Particularly we have found that the nature of the different SAHCs is strongly dependent on the matrix as it affects the charge and position of the atomic levels. In addition, the matrix atoms can also participate in the reactions which has an impact on the overall SAHC reactivity illustrated by the interaction with hydrogen. With respect to SAHC stability, the major threat to these compounds, the most favourable case is found when cationic (still active) species are formed since coalescence is prevented by electrostatics.

The development of high-efficiency and low-cost catalysts for hydrogen release from chemical hydrogen-storage materials is essential for the hydrogen-economy paradigm. Herein, we report a facile and controllable method to fabricate a series of Co-doped nickel phosphides and their corresponding nanohybrids with graphene oxide (GO) as highly efficient, robust and noble-metal-free catalysts for ammonia borane hydrolysis. The incorporation of Co into Ni2P effectively optimizes the electronic structures of Ni2−xCoxP catalysts to enhance their interaction with AB and simultaneously facilitate the hydroxyl activation of AB, resulting in the reduction of the reaction energy barrier and thus substantial improvement of the catalytic rate.

State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes usually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core–shell Fe2O3/Fe2TiO5 type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm−2 at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of Fe2TiO5 and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the Fe2O3/Fe2TiO5/ CoFe-PBA heterostructure reveals that the surface states’ electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO, Grants CTQ2015-71287-R, CTQ2015-71287-R, and CTQ2015-68770-R) and the coordinated Project ValPEC (ENE2017-85087-C3), the BIST Ignite Project inWOC2 and the Generalitat de Catalunya (2017 SGR 90, 2017 SGR 327, 2017 SGR 329, 2017 SGR 1246, and 2017 SGR 1406). ICN2 acknowledges the support from the Severo Ochoa Program (MINECO, Grant SEV-2017-0706). ICN2, ICIQ, and IREC are funded by the CERCA Programme/Generalitat de Catalunya. P.Y.T. acknowledges the scholarship support of DAAD short term grant. H.C.D. acknowledges support from the Deutsche Forschungsgemeinschaft (SFB 917). F.S.H. thanks the “LaCaixa”-Severo Ochoa International Programme (Programa internacional de Becas “LaCaixa”- Severo Ochoa) for a Ph.D. fellowship. P.P. and M.H. thank for the support by the Federal Ministry for Economic Affairs and Energy (BMWi) (Fundingregistration number: 03ET6080E). M.L. thanks the COST Action StableNextSol project MP1307, supported by COST (European Cooperation in Science and Technology). H.X. acknowledges the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295 for the postdoctoral contract.

The methoxycarbonylation of toluenediamines with dialkyl carbonates constitutes an alternative route for the phosgene-free production of isocyanate precursors. Despite the remarkable catalytic activity of ceria in the reaction, achieving full selectivity and long-term stability still represent major challenges. Here, the mechanism of the methoxycarbonylation of the industrially relevant 2,4-diaminotoluene (2,4-TDA) with dimethylcarbonate (DMC) along with the evolution of the property−performance interplay upon consecutive cycles are rationalized via the identification of reaction products, characterization tools, and density functional theory (DFT). The formation of the desired carbamates (7% mono- and 83% biscarbamate) is favored over the (111) facet, the most abundant in the as-prepared material, and proceeds via a complex reaction mechanism that involves a broad number of isomers and multiple reaction paths. A consecutive reaction in which 2,4-TDA is converted into a monocarbamate that further reacts to the biscarbamate drives the selective path. Part of these carbamates reacts to form productive ureas, unprecedented intermediates that reversely transform into carbamates. A full product analysis enables us to identify a number of side products that mostly comprises N-methylated carbamates and N-methylated ureas. Evaluation in subsequent cycles evidences the catalyst deactivation and the concomitant increase in the formation of byproducts, which is linked to the increasing amount of carbon deposits along with the DMC-induced partial surface restructuring into an oxygen-defective (100) facet after six cycles. These findings highlight the challenges in the rational design of robust heterogeneous catalysts for the production of isocyanate precursors.

Chemical Science, 10 (2), ISSN:2041-6520, ISSN:2041-6539

Single-atom heterogeneous catalysts with welldefined architectures are promising for deriving structure– performance relationships, but the challenge lies in finely tuning the structural and electronic properties of the metal. To tackle this point, a new approach based on the surface diffusion of gold atoms on different cavities of N-doped carbon is presented. By controlling the activation temperature, the coordination neighbors (Cl, O, N) and the oxidation state of the metal can be tailored. Semi-hydrogenation of various alkynes on the single-atom gold catalysts displays substratedependent catalytic responses; structure insensitive for alkynols with g-OH and unfunctionalized alkynes, and sensitive for alkynols with a-OH. Density functional theory links the sensitivity for alkynols to the strong interaction between the substrate and specific gold-cavity ensembles, mimicking a molecular recognition pattern that allows to identify the cavity site and to enhance the catalytic activity.

In the context of vinyl chloride monomer (VCM) production, an oxychlorination catalyst that allows direct VCM formation from gas-derived ethane instead of expensive oil-derived ethene is intensively sought after. A wide range of stable ethane oxychlorination catalysts for this purpose have recently been reported, yet they mainly yield ethene, while VCM remains a minor by-product. Strikingly, the same catalysts are active in ethene oxychlorination, resulting in selective VCM formation under equivalent reaction conditions. This work reveals the origin of these diverging selectivity patterns by combining quantitative catalytic tests, temporal analysis of products (TAP), and density functional theory (DFT) on iron phosphate. Ethane oxychlorination is found to proceed sequentially through ethyl chloride (EtCl) dehydrochlorination to ethene, while ethene oxychlorination directly yields VCM without formation of the intermediate dichloroethane (EDC) on iron phosphate. Furthermore, by co-feeding ethane in ethene oxychlorination, we demonstrate that the alkane suppresses the formation of VCM in ethene oxychlorination. The reason for this VCM inhibition is found in the hydrocarbon competition for a combination of the active, free and chlorinated iron centers. As ethane activation exhibits half of the barrier of ethene activation, the presence of ethane leads to active site depletion, hindering VCM formation. These observations are extended by ethane co-feeding tests in ethene oxychlorination over a wide range of known oxychlorination catalysts (EuOCl, LaOCl, CeO2, and CuCl2-KCl-LaCl3/c-Al2O3), and corresponding DFT calculations, indicating that the described phenomenon is material independent. The gathered molecular-level understanding explains the major hurdle of using ethane as feedstock for vinyl chloride production.

Graphene decorated with isolated single atoms (SAs) offers new vista to magnetic and spintronic devices up to single-atom catalysts. While sp atoms can be efficiently bound to graphene, d-block atoms require anchoring groups to prevent nanoparticle formation. Identification of suitable binding sites is a challenging task because the interaction among graphene, anchoring groups and adatoms is very complex. Using density functional theory (DFT) we explored strength and nature of interactions of graphene covalently functionalized by − OH, − CN, − F, and − H groups as anchors for Pt SAs. Both theory and experiment showed that − CN groups acted as suitable ligand enabling immobilization of 3.7 wt % single Pt adatoms. The findings imply that CN functionalized graphene, i.e., cyanographene, is a perspective material for anchoring metal adatoms with potential implications as single-atom-catalysts.

Increasing the activity of the nitrogen reduction reaction while slowing the detrimental hydrogen evolution reaction is a key challenge in current electrocatalysis to provide a sustainable route to ammonia. Recently, nanoparticles in ionic liquid (IL) environments have been found to boost the selectivity of electrochemical synthesis of ammonia from dinitrogen at room temperature. Here, we use for the first time a fully atomistic representation of metal−IL interfaces at the density functional theory level to understand experimental evidence, with particular focus on the rate and selectivity determining formation of N2H intermediates compared to hydrogen evolution. We find that decorating the metal surface with fluorinated ILs creates specific H-bond interactions between Ru−N2H and IL anions, stabilizing this intermediate and thus driving the selectivity of the electrochemical process.

Nitric oxide disproportionation at the site-isolated Fe centers of the metal organic framework material known as Fe-MOF-5 has been explored with density functional theory (DFT). The computed reaction sequence supports the mechanism suggested by experiment that involves the formation of the monoanionic hyponitrite radical. The validity of the computed reaction mechanism is bolstered by impressive agreement between computed and experimental vibrational spectroscopic evidence of each reaction step. Similarly the analogous MnII-MOF-5 system indicates that the disproportionation of NO should proceed smoothly with this single-site material. These results, observed also for some homogeneous Mn(II) catalysts, indicate that heterogeneous Mn-based materials could be employed as efficient biological and industrial catalytic systems in NO disproportionation processes.

Controlling the structure sensitivity of catalyzed reactions over metals is central to developing atom-efficient chemical processes. Approaching the minimum ensemble size, the properties enter a non-scalable regime in which each atom counts. Almost all trends in this ultra-small frontier derive from surface science approaches using model systems, because of both synthetic and analytical challenges. Exploiting the unique coordination chemistry of carbon nitride, we discriminate through experiments and simulations the interplay between the geometry, electronic structure, and reactivity of palladium atoms, dimers, and trimers. Catalytic tests evidence applicationdependent requirements of the active ensemble. In the semihydrogenation of alkynes, the nuclearity primarily impacts activity, whereas the selectivity and stability are affected in Suzuki coupling. This powerful approach will provide practical insights into the design of heterogeneous catalysts comprising well-defined numbers of atoms.