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The purpose of this study was to describe the evolution of meningococcal disease (MD) in the city of Barcelona between 1988 and 2015 and to assess the impact of the vaccine against serogroup C.The evolution of MD and by serogroup was analysed using the information included in the mandatory notification diseases registry. Incidences of all serogroups between the periods of before and after the implementation of the serogroup C vaccine in 2000 were compared. Vaccination coverage among cases, serogroup among vaccinated cases and mortality and case fatality rates were analysed.MD has evolved from an incidence rate in children aged under 1 of 63.09 cases per 100,000 in 1997-2000 to 15.44 per 100,000 in 2001-2015. All MD serogroups incidences decreased after the implementation of the vaccine, especially for serogroup C among children aged between 1 and 4. Since 2000 vaccine coverage in MD cases by this serogroup was 7.6% while in those affected by serogroup B it was 35.0% (p.01). Among those vaccinated, 66.4% of cases were serogroup B and 5.2% were C (p.01). Mortality and case fatality rates were 7.7% and 0.19/100,000 respectively, without significant changes in time regarding case fatality.Incidence caused by serogroups B and C has decreased after the systematic vaccination against serogroup C. Vaccination against serogroup B could further reduce the impact of this lethal disease which has not decreased during this period.

Solvation is crucial in many chemical and electrochemical processes related to alcohol conversion on metal surfaces. Particularly, understanding the dehydrogenation mechanism of methanol on solvated Pd, Pt, and Ru surfaces could allow the design of efficient methanol fuel cells. The large computational cost related to adopting an explicit solvation approach into density functional theory can be reduced drastically by using implicit solvation methods. In this study, we use our recently developed continuum solvation model (MGCM) to elucidate the minimum number of explicit water molecules to add to the solvated methanol/metal surface systems to reproduce experimental data with an optimized balance between time and reliability. Our results stress the importance of adding two explicit water molecules, especially for the case of Ru surfaces. For this later system, we provide a first insight into the decomposition mechanism of methanol using first-principles calculations. Our predictions can be then a useful reference for future studies that aim at designing more efficient heterogeneous catalysts with solvents.

Secondary phosphine oxides (SPOs) can be used as ligands to stabilize catalytically active gold nanoparticles (AuNPs). These materials are active and very selective in the chemoselective hydrogenation of acrolein and other α,β-unsaturated aldehydes, but the origin of the activity remains elusive. Here, by means of density functional theory, we identify a cooperative effect at the AuNP−SPO interface that enables the heterolytic cleavage of the H2 molecule and its kinetically favorable concerted addition to the CO bond (in a transfer hydrogenation-like mode) to form the corresponding allyl alcohol. From the mechanism it is possible to identify the descriptors that explain the activity for a family of SPO-stabilized AuNPs and a set of unsaturated aldehydes. The activity depends on the basicity difference between ligand and reactant and the sites available on the nanoparticle.

Ligand-modified palladium nanoparticles deposited on a carbon carrier efficiently catalyze the direct synthesis of H2O2 and the unique performance is due to their hybrid nanostructure. Catalytic testing demonstrated that the selectivity increases with the HHDMA ligand content from 10% for naked nanoparticles up to 80%, rivalling that obtained with state-of-the-art bimetallic catalysts (HHDMA=C20H46NO5P). Furthermore, it remains stable over five consecutive reaction runs owing to the high resistance towards leaching of the organic moiety, arising from its bond with the metal surface. As rationalized by density functional theory, this behavior is attributed to the adsorption mode of the reaction intermediates on the metal surface. Whereas they lie flat in the absence of the organic shell, their electrostatic interaction with the ligand result in a unique vertical configuration which prevents further dissociation and over-hydrogenation. These findings demonstrate the importance of understanding substrate–ligand interactions in capped nanoparticles to develop smart catalysts for the sustainable manufacture of hydrogen peroxide.

Indium oxide catalyzes acetylene hydrogenation with high selectivity to ethylene (>85%); even with a large excess of the alkene. In situ characterization reveals the formation of oxygen vacancies under reaction conditions, while an in depth theoretical analysis links the surface reduction with the creation of well-defined vacancies and surrounding In3O5 ensembles, which are considered responsible for this outstanding catalytic function. This behavior, which differs from that of other common reducible oxides, originates from the presence of four crystallographically inequivalent oxygen sites in the indium oxide surface. These resulting ensembles are 1) stable against deactivation, 2) homogeneously and densely distributed, and 3) spatially isolated and confined against transport; thereby broadening the scope of oxides in hydrogenation catalysis.

Gamma-valerolactone (GVL), a versatile renewable compound listed among the top 10 most promising platform chemicals by the US Department of Energy, is produced via hydrogenation of levulinic acid (LA). The traditional high-loading ruthenium-on-carbon catalyst (5 wt% Ru) employed for this transformation suffers from low metal utilisation and poor resistance to deactivation due to the formation of RuOx species. Aiming at an improved catalyst design, we have prepared ruthenium nanoparticles modified with the water-soluble hexadecyl(2-hydroxyethyl)dimethylammonium dihydrogen phosphate (HHDMA) ligand and supported on TiSi2O6. The hybrid catalyst has been characterised by ICP-OES, elemental analysis, TGA, DRIFTS, H2-TPR, STEM, EDX, 31P and 13C MAS-NMR, and XPS. When evaluated in the continuous-flow hydrogenation of LA, the Ru-HHDMA/TiSi2O6 catalyst (0.24 wt% Ru) displays a fourfold higher reaction rate than the state-of-the-art Ru/C catalyst, while maintaining 100% selectivity to GVL and no sign of deactivation after 15 hours on stream. An in-depth molecular analysis by Density Functional Theory demonstrates that the intrinsic acidic properties at the ligand–metal interface under reaction conditions ensure that the less energy demanding path is followed. The reaction does not obey the expected cascade mechanism and intercalates hydrogenation steps, hydroxyl/water eliminations, and ring closings to ensure high selectivity. Moreover, the interfacial acidity increases the robustness of the material against ruthenium oxide formation. These results provide valuable improvements for the sustainable production of GLV and insights for the rationalisation of the exceptional selectivity of Ru-based catalysts.

The realization of artificial photosynthesis may depend on the efficient integration of photoactive semiconductors and catalysts to promote photoelectrochemical water splitting. Many efforts are currently devoted to the processing of multicomponent anodes and cathodes in the search for appropriate synergy between light absorbers and active catalysts. No single material appears to combine both features. Many experimental parameters are key to achieve the needed synergy between both systems, without clear protocols for success. Herein, we show how computational chemistry can shed some light on this cumbersome problem. DFT calculations are useful to predict adequate energy-level alignment for thermodynamically favored hole transfer. As proof of concept, we experimentally confirmed the limited performance enhancement in hematite photoanodes decorated with cobalt hexacyanoferrate as a competent water-oxidation catalyst. Computational methods describe the misalignment of their energy levels, which is the origin of this mismatch. Photoelectrochemical studies indicate that the catalyst exclusively shifts the hematite surface state to lower potentials, which therefore reduces the onset for water oxidation. Although kinetics will still depend on interface architecture, our simple theoretical approach may identify and predict plausible semiconductor/catalyst combinations, which will speed up experimental work towards promising photoelectrocatalytic systems.

Journal of Catalysis, 353, ISSN:0021-9517, ISSN:1090-2694

Advanced Functional Materials, 27 (8), ISSN:1616-3028, ISSN:1616-301X

We present the ioChem-BD platform (www. iochem-bd.org) as a multiheaded tool aimed to manage large volumes of quantum chemistry results from a diverse group of already common simulation packages. The platform has an extensible structure. The key modules managing the main tasks are to (i) upload of output files from common computational chemistry packages, (ii) extract meaningful data from the results, and (iii) generate output summaries in user-friendly formats. A heavy use of the Chemical Mark-up Language (CML) is made in the intermediate files used by ioChem-BD. From them and using XSL techniques, we manipulate and transform such chemical data sets to fulfill researchers’ needs in the form of HTML5 reports, supporting information, and other research media. &nbsp

Despite its ubiquity in homogeneous and enzymatic catalysis, concerted mechanisms have been overlooked for heterogeneously catalyzed reactions. The elusive nature of transition states leaves Density Functional Theory, DFT, as the only robust tool for their identification and characterization. By means of this method, we show that a concerted path takes part in the recently discovered semihydrogenation of propyne on CeO2, for which an excellent activity and selectivity have been reported. The high surface H coverage imposed by the experimental hydrogenation conditions induces site isolation and drives the reaction through a six-membered ring transition state. This unprecedented pathway accounts for many of the experimental observations, such as the unique syn-stereoselectivity, the excellent alkene selectivities, or the high temperature and large H2/alkyne ratios required.

Linear-scaling relationships are powerful tools in the rational design of new catalysts. Few of these thermodynamic relationships consider multifunctionalized molecules, and none deal with intramolecular interactions such as hydrogen bonds, widely present in polyoxygenated molecules obtained from renewable sources. We have completed an adsorption database with 14 mono- and polyalcohols up to four carbon atoms, on clean Pt and Pd(111) surfaces, using periodic density functional theory, and including van der Waals terms, and we have obtained results that are in good agreement with experimental data. With this data, we propose a robust multifactorial linear-scaling relationship, which is an additive function of the contributions from hydroxyl and CHx groups and the hydrogen bonds. We have validated the model by comparison with experiments and by the prediction of adsorption energies of C4–C7 sugar alcohols on both surfaces. Our study paves the way for the study of large multifunctionalized molecules, like th...

The theoretical study of catalysis would substantialy benefit from the use of atomistic simulations that can provide information beyond mean-field approaches. To date, the nanoscale understanding of surface reactions has been only qualitatively achieved by means of kinetic Monte Carlo coupled to density functional theory, KMC-DFT. Here, we examine a widely employed model for oxygen interaction with the RuO2(110) surface, a highly anisotropic system. Our analysis reveals several covert problems that render as questionable the model’s predictions. We suggest an advanced approach that considers all the relevant elementary steps and configurations while smoothing the intrinsic errors in the DFT description of oxygen. Under these conditions, KMC provides quantitative agreement to temperature-programmed desorption experiments. These results illustrate how KMC-based simulations can be pushed forward so that they evolve toward being the standard methodology to study complex chemistry at the nanoscale.

Mechanisms for H2 dissociation on metal oxides have been typically inferred from the infrared spectra of reaction products on the basis of the presence or lack of M–H fingerprints. Here, we demonstrate by means of density functional theory that oxides with polar M–O bonds might favor heterolytic dissociation. Moreover, we report that the resulting heterolytic product can further evolve to the homolytic one provided that metal ions are reducible. Hence, it follows that the redox capacity of the metal determines the reaction outcome. This finding sheds light on why both M–H and O–H bands appear in the infrared spectra of nonreducible oxides such as MgO or γ-Al2O3, while only O–H bands are observed for reducible oxides like CeO2. It results in a unified mechanism for polar oxides that can be generalized to other materials exhibiting significant charge separation. Importantly, we also show that the low activity of CeO2 toward H2 can be improved by enhancing the basicity of surface O atoms upon lattice expansi...

We investigated which factors govern the critical steps of cation exchange in metal-organic frameworks by studying the effect of various solvents on the insertion of Ni(2+) into MOF-5 and Co(2+) into MFU-4l. After plotting the extent of cation insertion versus different solvent parameters, trends emerge that offer insight into the exchange processes for both systems. This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials.

The adsorption of the first water layer on metals combines several structural motifs like pentagons, hexagons, and heptagons interconnected variably leading to a myriad of patterns. Although theoretical methods are now able to discriminate the ground states, there is a need to find simple ways to account for the relative stability of different patterns on the surface. Taking the already reported structures for water bilayers as training sets we have decomposed the adsorption energy of each of the motifs to their fundamental components: water-water and water-metal interactions through strain-induced surface metal deformations. Models coming from this scheme can be used to survey the properties of many of the structures reported irrespectively of their complexity, thus providing a simple structure-based tool to assess the likeliness, relative stability, wettability, and main patterns of water motifs in metals.

Several works in literature demonstrated that catalytic ozonation using metal ions promotes the decomposition of ozone and generation of hydroxyl radicals (HO•). The purpose of this study was to assess the effects of different metal ions (Fe2+, Co2+ and Al3+) in disinfection of urban wastewater through E.coli and Pseudomonas spp inactivation along with cellular adenosine triphosphate (ATP) depletion. Simultaneously, the effect of catalytic ozonation of secondary effluent on the selected micropollutants removal with different ozone kinetics (acetamiprid, dichlorvos and atrazine) was evaluated in semi-continuous operation. Results demonstrated that E.coli and Pseudomonas spp inactivation increased almost 20% with 1 mg L−1 Fe2+, Co2+, Al3+ and 40% with 10 mg L−1 Fe2+ compared with single ozonation. Fe2+ was the most effective metal ion on inhibiting regrowth after the treatments. The cellular ATP followed the same trend as the indicators microorganisms inactivation, with significant reduction of ATP over the treatment to single ozonation comparison. The ROH,O3 was applied for the treatments to quantify and compare the micropollutants removal by the radical pathway. The improvement of metal ions on ROH,O3 values occurred significantly for both stages of ozonation (before and after initial ozone demand) for all tested metals. Thus, metal ions addition to ozonation process provided an increase in simultaneous disinfection and pesticides removal as well as in the inhibition of bacterial reactivation, which resulted in savings between 30–50% of ozone dose needs compared with the same attainment in single ozonation.

IrO2 has been investigated as alternative rutile-type catalyst to RuO2 for gas-phase HCl oxidation. The HCl conversion level over IrO2 at 723 K was comparable to that of RuO2 at ca. 170 K lower temperature, in line with the higher computed energy barrier for chlorine evolution over the former oxide. Similarly to RuO2, chlorination took place only at the IrO2 surface, which is predicted to exhibit full occupation of the coordinatively unsaturated iridium sites and replacement of 50% of the oxygen bridge positions by chlorine. Advantageously, IrO2 is more resistant than RuO2 against oxidation, since the latter forms volatile RuO4 species at high temperatures. IrO2 (2 wt %) supported on TiO2-rutile displayed a 6 times higher activity than on TiO2-anatase. Although this corroborates the crucial role of the structural similarity between the carrier and active phase highlighted in the development of RuO2-based catalysts, some differences were uncovered. (i) Small and highly dispersed IrO2 clusters rather than t...

Oxides at the nanometric scale show a behavior markedly different from that of their bulk counterparts. Ultrathin oxides grown on metals do not reach the full insulator regime, and they cannot decouple the electronic clouds of incoming adsorbates from that of the metal substrate. Although oxygen vacancies control the chemical and physical properties of ultrathin oxide films, the role of intrinsic defects has been overlooked so far. By means of density functional theory methods, we show that the addition of atoms with high electron affinity, such as Au, to ultrathin MgO grown either on a Ag or Mo support, completely reverses the preferential positions of oxygen vacancies, decreases their residual charge, and enhances their mobility. Oxygen vacancies behave completely different for the MgO/M systems compared to the Au/MgO/M systems, which opens a new way to tune the reactivity of adsorbates.

Seed-mediated growth is the most efficient methodology to control the size and shape of colloidal metal nanoparticles. In this process, the final nanocrystal shape is defined by the crystalline structure of the initial seed as well as by the presence of ligands and other additives that help to stabilize certain crystallographic facets. We analyze here the growth mechanism in aqueous solution of silver shells on presynthesized gold nanoparticles displaying various well-defined crystalline structures and morphologies. A thorough three-dimensional electron microscopy characterization of the morphology and internal structure of the resulting core-shell nanocrystals indicates that {100} facets are preferred for the outer silver shell, regardless of the morphology and crystallinity of the gold cores. These results are in agreement with theoretical analysis based on the relative surface energies of the exposed facets in the presence of halide ions.

Tin oxide (SnO2) represents a major fraction of research for developing solid-state gas sensors. Nevertheless, a detailed insight into the chemical-to-electrical transduction mechanisms between ammonia (NH3) molecules and this metal oxide is still limited. Here, the adsorption of NH3 on SnO2 was examined by density functional theory (DFT) calculations and confronted to experimental data obtained with individual nanowire devices. It was concluded that under real working conditions nonlattice oxygens (O5c) adsorbed on SnO2 exhibit a more basic character than lattice bridging oxygens (O2c), and consequently, they play a key role in the dehydrogenation of NH3 on SnO2, with N2 and H2O as the main resulting products. The sensing process of ammonia on tin oxide nanowires not only involves physical mechanisms but also has a concomitant chemical nature that requires two molecules of NH3 for the reaction to take place. Our theoretical modeling reveals why ammonia sensing is competitive to the adsorption of water mo...

Metal–organic frameworks with open metal sites such as Cu-BTC have the potential to improve separations of molecules of differing polarities. In the Cu-BTC structure, molecules with high dipole moment such as water are preferentially adsorbed in the cages containing the open metal sites, while less polar molecules such as alcohols can be adsorbed in the other cages. We combine Monte Carlo simulations and ab initio calculations with the aim of tuning the adsorption properties of Cu-BTC (a) via selective blockage of cages or (b) poisoning the open metal centers. The simulation results propose selective blocking and screening of the active sites as good strategies to enhance the alcohol/water selectivity in the gas and liquid phase as well as the water resistance of the structure.

Surface structure controls the physical and chemical response of materials. Surface polar terminations are appealing because of their unusual properties but they are intrinsically unstable. Several mechanisms, namely metallization, adsorption, and ordered reconstructions, can remove thermodynamic penalties rendering polar surfaces partially stable. Here, for CeO2(100), we report a complementary stabilization mechanism based on surface disorder that has been unravelled through theoretical simulations that: account for surface energies and configurational entropies; show the importance of the ion distribution degeneracy; and identify low di usion barriers between conformations that ensure equilibration. Disordered configurations in oxides might also be further stabilized by preferential adsorption of water. The entropic stabilization term will appear for surfaces with a high number of empty sites, typically achieved when removing part of the ions in a polar termination to make the layer charge zero. Assessing the impact of surface disorder when establishing new structure–activity relationships remains a challenge.

Catalytic materials are complex systems that contain different units, typically a carrier and an active phase. For many reactions, redox-active materials constitute the active phase. Active catalytic phases based on metal oxides include, but are not limited to, silver, copper, vanadium, molybdenum, iron, cobalt, and titanium oxides, and most notably ceria.(1, 2) This results in variable occupations of the d or f states of the cations. Therefore, the proper energy alignment of these states is mandatory for the adequate description of the chemistry responsible for the catalytic processes. In particular, all the challenges related to energy-harvesting and storage technologies are intrinsically linked to the small energy difference between the different spin configurations, the easy transfer between them, and the correct alignment of the energy states.

In September 2014, university professors from UAB (Universitat Autonoma de Barcelona) and teacher educators from CESIRE (Centre for Support of Educational Innovation and Research) started to collaborate in the design of a primary teacher development program called “IBS and English learning in primary education”. One of the goals of this program was to create a sustainable triadic partnership (Primary school teachers/UAB university professors, researchers, and primary student teachers/CESIRE’s teacher educators) which fosters educational innovations and research in the integration of Inquiry based science and English in primary education in Catalan schools. The triadic partnership, piloted for the first aim in the academic year 2014–2015, has provided a scenario for successful collaborative and innovative teacher development processes. The first strength of the teacher preparation model has been the explicit theoretical support provided by university and teacher educators from both science and foreign language education. The theory acted as an arena where to create a boundary object that was shared and negotiated among all participants. The boundary object was supported by the theoretical framework of the program and by the development of a tool used by all participants. This tool was designed to guide the planning of the Inquiry Based Science instructional unit in English and it will be refined in the next future theoretically and practically. The second strength of the program has been the composition of the learning community including school teachers, student teachers, university professors and teacher educators from both science and language education disciplines.

Surface structure controls the physical and chemical response of materials. Surface polar terminations are appealing because of their unusual properties but they are intrinsically unstable. Several mechanisms, namely metallization, adsorption, and ordered reconstructions, can remove thermodynamic penalties rendering polar surfaces partially stable. Here, for CeO

SnO2 NWs networks on heated micromembranes have been characterized as ammonia sensors. The approach allows achieving reproducible growth and stable and long-lasting ammonia sensors with site- specific grown SnO2 NWs. The devices have been tested both in dry and humid conditions showing response time down to two minutes. Sensors have been tested up to 1 month, only presenting variation of the base resistance with full retention of the response towards the gaseous analytes. Different concur- rent sensing mechanisms have been identified relating the determined sensing kinetics with previous theoretical calculations. Specifically, oxygen dissociation seems to play a key role in the overall ammonia sensing sequence. In humid conditions, moisture reduces the response to ammonia but also lowers the activation energy of the reaction process.

Catalytic HBr oxidation is an integral step in the bromine-mediated functionalisation of alkanes to valuable chemicals. This study establishes the relationships between the mechanism of HBr oxidation over rutile-type oxides (RuO2, IrO2, TiO2) and their apparent catalytic performance. Comparison with the well-studied HCl oxidation revealed distinct differences in surface chemistry between HBr and HCl oxidation that impact the stability and activity of the catalysts. The kinetic fingerprints of both oxidation reactions over the three rutile-type oxides investigated are compared using temporal analysis of products, which substantiates the energy profiles derived from density functional theory. The quantitative determination of the halogen uptake under operando conditions using prompt gamma activation analysis demonstrates that RuO2 suffers from extensive subsurface bromination upon contact with hydrogen bromide, particularly at low temperature and low O2 : HBr ratios, which negatively affects the stability of the catalyst. TiO2 exhibits intrinsically low halogen coverage (30–50%) under all the conditions investigated, due to its unique defect-driven mechanism that renders it active and stable for Br2 production. On the contrary, for HCl oxidation TiO2 is inactive, and the chlorination of the highly active RuO2 is limited to the surface. Differences in the extent of surface halogenation of the materials were also confirmed by high-resolution transmission electron microscopy and explained by the DFT calculations. These insights into the molecular-level processes taking place under working conditions pave the way for the design of the next generation catalysts for bromine production.

Selective hydrogenations lay at the heart of many industrial processes. The archetypal catalysts for this class of reactions are generally prepared by ‘metal poisoning’ strategies: the active metal is protected and selectively deactivated with vari- ous compounds. This approach has been applied for decades, with limited understanding. Low product selectivity and pres- ence of toxic elements in the catalyst pose severe constraints in the utilization of these materials in the future. Thus, to de- velop more sustainable catalysts, this field has recently gained momentum. This Review analyzes the concepts and frontiers that have been developed in the last decade: from nanostruc- turing less conventional metals in order to improve their ability to activate H2, to the use of oxides as active phases, from alloy- ing, to the ensemble control in hybrid materials, and site isola- tion approaches in single-site heterogeneous catalysts. Particu- lar attention is given to the hydrogenation of alkynes and ni- troarenes, two reactions at the core of the chemical industry, importantly applied in the manufacture of polymers, pharma- ceuticals, nutraceuticals, and agrochemicals. The strategies here identified can be transposed to other relevant hydrogena- tions and can guide in the design of more advanced materials.

The relationship between the homogeneous and heterogeneous phases of a catalyst is widely neglected in part due to the inherent differences between the experimental and theoretical techniques employed to study them. It is well- known that, under reaction conditions, many homogeneous catalysts deactivate and generate black metals (i.e., nano- particles). Simultaneously, heterogeneous catalysts tend to suffer of leaching processes under harsh conditions, which produce the formation of species in the homogeneous phase (i.e., volatile or organometallic species). To unravel the links between these two types of catalytic species, we have taken PdAu catalysts in the oxidation of crotyl alcohol to crotonaldehyde and investigated the reaction process for both homogeneous and heterogeneous phases. We show that the process is possible in both phases and, essentially, contains the same elementary steps. The results indicate that the homogeneous catalyst is slightly more active; however, the enhanced stability of the heterogeneous phase provides a better performance under relevant reaction conditions. Both catalytic systems are connected through two simple steps that can be computed: oxidative leaching and deposition. The oxidative leaching of the PdAu nanoparticles in the presence of dioxygen can produce Pd(II) monomeric species able to catalyze the alcohol oxidation in homogeneous conditions. After the reaction the reduced Pd(0) homogeneous catalyst is reabsorbed onto the PdAu nanoparticles, preventing the aggregation process. The present work shows that the full homogeneous/heterogeneous catalytic cycle can be analyzed in a holistic manner with computational techniques.

Increasing the resistance to humid environments is mandatory for the implementation of isoreticular metal-organic frameworks (IRMOFs) in industry. To date, the causes behind the sensitivity of [Zn(4)(μ(4)-O)(μ-bdc)(3)](8)(IRMOF-1; bdc=1,4-benzenedicarboxylate) to water remain still open. A multiscale scheme that combines Monte Carlo simulations, density functional theory and first-principles Born-Oppenheimer molecular dynamics on IRMOF-1 was employed to unravel the underlying atomistic mechanism responsible for lattice disruption. At very low water contents, H(2)O molecules are isolated in the lattice but provoke a dynamic opening of the terephthalic acid, and the lattice collapse occurs at about 6% water weight at room temperature. The ability of Zn to form fivefold coordination spheres and the increasing basicity of water when forming clusters are responsible for the displacement of the organic linker. The present results pave the way for synthetic challenges with new target linkers that might provide more robust IRMOF structures.

The interaction of a single formaldehyde or methanol molecule with a bare and a water-covered Pt(111) surface has been investigated using density-functional calculations, including the contribution of dispersion forces. van der Waals (vdW) terms are found to be essential to obtain the adsorption energies of both isolated molecules to the Pt(111) surface and the water wetting layer in agreement with experimental data. Moreover, the vdW correction changes completely the view on the mixed molecule–water–surface adsorption profile. In turn, the change induced by the vdW-forces on the geometric properties is very small for the minima found. For the water-covered surface, pure density-functional calculations underestimate the binding energy of a wetting-layer on Pt(111) by about 140 meV/H2O molecule. The dispersion corrected calculations reveal a binding energy of 0.61 eV/H2O molecule of a water bilayer at the platinum (111) surface, which is in perfect agreement with the experimental lattice energy of bulk ice...

Partial hydrogenation of unsaturated hydrocarbons comprises an important family of reactions that are applied in many industrial sectors. Understanding the hydrogenation of polyunsatured and polyunsaturated compounds on heterogeneous catalysts at its molecular level remains a challenging milestone to fine-tune the product distribution. Our study presents a detailed mechanistic analysis of the gas phase hydrogenation of vinylacetylene (1-butene-3-yne) and valylene (2-methyl-1-butene-3-yne) over palladium and copper catalysts. These two metals are selected owing to their pronounced differences in continuous flow catalytic tests at ambient pressure. The chemoselectivity, regioselectivity, isomerization, and oligomerization patterns measured in a broad range of feed hydrogen/hydrocarbon ratios are rationalized by density functional theory simulations. An extended Bronsted–Evans–Polanyi relationship for both substrates and active metals is found for the hydrogenation processes. The identified factors that govern selectivity are similar to those identified for smaller C2 and C3 compounds and, thus, a means of systematization to other polyunsaturated compounds is opened up.

The mechanisms of direct N 2 O decomposition and N 2 O reduction by H 2 or NH 3 on RuO 2 has been studied by means of steady-state catalytic tests at ambient pressure, transient experiments in a temporal analysis of products (TAP) reactor, and density functional theory (DFT) simulations. Bulk RuO 2 is very active for N 2 O decomposition into N 2 and O 2 , achieving full conversion at 723 K. According to the DFT calculations, coordinatively unsaturated ruthenium (Ru cus ) sites are active for the decomposition and oxygen elimination from the surface is rate-limiting step. When pre-reducing RuO 2 with H 2 , the de-N 2 O activity in the low-temperature region increases. This is attributed to the higher reactivity of surface oxygen vacancies created by H 2 at bridge sites compared to Ru cus sites. Co-feeding of hydrogen or ammonia with nitrous oxide strongly accelerates the rate of N 2 O elimination. TAP studies show that oxygen species formed upon N 2 O decomposition over RuO 2 react with NH 3 and H 2 yielding N 2 , NO, N 2 O, and H 2 O. Both TAP experiments and DFT simulations show that the N-containing intermediates coming from ammonia adsorb much stronger on the catalyst surface than H-containing intermediates coming from hydrogen. This causes blockage of active sites for N 2 O decomposition by the former species, accounting for the higher efficiency of H 2 as reductant for N 2 O. The presence of O 2 in the feed cancels the reducing effect of H 2 or NH 3 due to the more favorable re-oxidation of reduced RuO 2 by O 2 compared to N 2 O.

We have investigated the full reaction path leading to the formation of HCN from ammonia and methane on Pt(111) by means of density functional theory. Industrially, the reaction can take place under oxidative or nonoxidative conditions, and thus, we have described the effect of oxygen in the reaction mechanism. DFT calculations show that the reaction network is very complex, including dehydrogenation steps, HxC−NHy (x = 0−2, y = 0−2) couplings, de/hydrogenation of C−N-containing species, and isomerization. Under nonoxidative conditions (Degussa process), the main reaction path for C−N formation takes place through partially hydrogenated compounds, in particular, those coming from HxC + NH2 (x = 0, 1) coupling with subsequent dehydrogenation of the resulting intermediate. Under oxygen-rich conditions (Andrussow), the main C−N bond formation step switches to HC + N or C + N. The mechanistic switch between oxidative and nonoxidative conditions is driven by the change in the relative stability of the intermed...

Temporary supply of CO during propyne hydrogenation over a copper-based catalyst derived from a Cu–Al hydrotalcite permanently increased the alkene selectivity from 60% to 92% at 100% alkyne conversion (473 K). The superior performance of the CO-modified copper catalyst (higher alkene selectivity and resistance against deactivation by fouling) was further confirmed at lower temperature (373 K). Our catalytic results suggested that carbon monoxide in the presence of propyne and hydrogen irreversibly restructures the catalyst surface leading to a smaller copper ensemble that minimizes C–C coupling. Consequently, the enhanced alkene production in the CO-modified catalyst was coupled to a decreased oligomer production and very little propane production. The pretreatment mixture, feed CO concentration, and type of alkyne are important aspects to attain a selective copper catalyst. The CO effect in alkyne hydrogenation over copper radically differs from that over palladium or nickel. On the latter two metals, the increased alkene selectivity in the presence of CO is mostly due to a reduction in the over-hydrogenation channel. In addition, the effect is fully reversible, that is, it vanishes on removing CO from the feed. The permanent modification of the copper ensemble by CO might be advantageous for (chemo) selective hydrogenations of high acetylenic substrates.

A Lindlar catalyst is a popular heterogeneous catalyst that consists of 5 wt.% palladium supported on porous calcium carbonate and treated with various forms of lead and quinoline. The additives strategically deactivate palladium sites. The catalyst is widely used for the partial hydrogenation of acetylenic compounds in organic syntheses. Alkyne reduction is stereoselective, occurring via syn addition to give the cis-alkene. Even if it has been employed for about 60 years, there is a lack of molecular level understanding of the Lindlar catalyst. We have applied density functional theory simulations to understand the structure and the nature of the interplay between the multiple chemical modifiers in the Lindlar catalyst. Indeed, the poisons influence different parameters controlling selectivity to the alkene: Pb modifies the thermodynamic factor and hinders the formation of hydrides, while quinoline isolates Pd sites thus minimizing oligomerization.

The pressure and materials gaps in heterogeneous catalysis often complicate the extrapolation of results from surface science experiments over single crystals to real catalysis at elevated pressure...

Alkyne hydrogenation, a widely used process in industry to purify olefin streams, comprises a prototype reaction to understand selectivity in heterogeneously catalyzed reactions. The selectivity of the reaction on palladium catalysts to the alkene, alkane, or oligomers strongly depends on the state of the (sub)surface; i.e. , the occurrence of complex carbide/hydride phases. In practice, hydrogenation reactors in C2 and C3 cuts of steam crackers require continuous CO feeding in order to enhance the alkene selectivity of palladium-supported catalysts. In the present work, we have studied the impact of carbon monoxide on the formation of carbide and hydride phases as a standpoint to derive structure–performance relationships under realistic process conditions. For this purpose, catalytic tests on a standard 1 wt.% Pd/Al 2 O 3 and Density Functional Theory on Pd(1 1 1) were combined. The influence of: (i) the alkyne (ethyne and propyne), (ii) the hydrogen:alkyne ratio (1–10), (iii) the carbon monoxide:hydrogen ratio (0–0.2), and (iv) the catalyst pretreatment on the product distribution was assessed in a continuous flow fixed-bed reactor at ambient pressure. In absence of CO, subtle changes in the hydrogen:alkyne ratio generate undesired products. Carbon monoxide enables the external control of the catalyst state by suppressing the formation of subsurface hydride and carbide phases, thereby stabilizing a high alkene yield in a broad range of feed hydrogen:alkyne ratios. This scenario contrasts with the more fragile regime of the hydride–carbide phases under CO-free conditions. DFT calculations obtained a single Bronsted–Evans–Polanyi relationship independently of the state of the catalyst (carbide, hydride, CO-covered) and the alkyne–alkene–alkane set (C2, C3).

The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al 2 O 3 and Cu/SiO 2 ). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N 2 adsorption, H 2 -TPR, XPS, and N 2 O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523 K using H 2 :C 3 H 4 ratios of 1–12 and were complemented by operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C 3 H 6 selectivity up to 80% at full C 3 H 4 conversion and stable performance in long-run tests at T ⩾ 473 K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites [S. Abello, D. Verboekend, B. Bridier, J. Perez-Ramirez, J. Catal. 259 (2008) 85] exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.