The hydrogenation of CO2 into hydrocarbons promoted by the action of sunlight has been studied on Co nanoparticles covered by thin carbon layers. In particular, nearly 100% selectivity to hydrocarbons is obtained with increased selectivity's towards C2+ hydrocarbons and alcohols (mainly ethanol) when using nanostructured materials comprising metallic cobalt nanoparticles, carbon layers, and sodium as promoter (Na-Co@C). In the contrary, larger amount of CH4 and lower selectivity to C2+ hydrocarbons and alcohols were obtained in the conventional thermal catalytic process. When using Co@C nanoparticles in the absence of Na or bare Co3O4 as catalyst, methane is essentially the main product (selectivity >96%). Control experiments in the presence of methanol as a hole scavenger suggest the role of light in generating charges by photon absorption via surface plasmon resonance as promoting factor. The reaction mechanism for photoassited CO2 hydrogenation on the Co-based catalysts were investigated by near ambient-pressure X-ray photoelectron (AP-XPS) and in situ Raman spectroscopies, which provided information on the role of light and Na promotor in the modulation of product distribution for CO2 hydrogenation. Spectroscopic studies suggested that surface CO2 dissociation to CO, the stabilization of CO adsorbed on the surface of Na-Co@C catalyst and the easy desorption of reaction products is a key step for photoassisted CO2 hydrogenation to ethanol and C2+ hydrocarbons.

Ruthenium nanoparticles with a core-shell structure formed by a core of metallic ruthenium and a shell of ruthenium carbide have been synthesized by a mild and easy hydrothermal treatment. The dual structure and composition of the nanoparticles have been determined by synchrotron XPS and NEXAFS analysis and TEM imaging. At increasing sample depth, metallic ruthenium species start to predominate, according to depth profile synchrotron XPS and XRD analysis. The herein ruthenium carbon catalyst is able to activate both CO2 and H2 showing exceptional high activity for CO2 hydrogenation at low temperatures (160-200 °C) with 100% selectivity to methane, surpassing by far the most active Ru catalysts reported up to now. Based on catalytic studies and isotopic 13 CO/ 12 CO2/H2 experiments, the active sites responsible for the unprecedented activity can be associated to those surface ruthenium carbide (RuC) species, enabling CO2 activation and transformation to methane via direct CO2 hydrogenation mechanism. The high activity and absence of CO in the gas effluent confers this catalyst interest for the Sabatier reaction, a reaction with renewed interest for storing surplus renewable energy in the form of methane.

Three cyclic trinuclear pyrazolate complexes with Au(I), Ag(I) or Cu(I) have been studied. These complexes have interesting and distinct optical and thermal properties depending on the metal, namely liquid crystalline behavior, red or deep-red phosphorescence at room temperature, thermoluminochromism and response to silver ions. The selected ligand, 4-hexyl-3,5-dimethylpyrazolate, maximizes the effect that the nature of the metals has on the properties of the complexes, thus allowing the intermolecular metallophilic interactions to be responsible for the optical properties. Moreover, the gold and silver complexes show columnar liquid crystal phases at high temperature. All of the complexes have good solubility properties for processing as poly(methyl methacrylate) (PMMA) doped films. Films of the gold, silver and copper complexes show interesting optical behavior such as wide-range color switching or phosphorescence turn-on upon cooling. In addition, films of the gold complex show a bright color switching (red to blue) in the presence of silver ions. The gold and copper complexes are bright phosphors with phosphorescent quantum yields of 90% in PMMA films, the highest values reported for this class of compounds at room temperature.

Enhanced methanol production is obtained over a non-promoted Cu–MgO–Al2O3 mixed oxide catalyst derived from a Cu–Mg–Al hydrotalcite precursor (HT) containing narrowly distributed small Cu NPs (2 nm). Conversions close to the equilibrium (∼20%) with a methanol selectivity of 67% are achieved at 230 °C, 20 bar, and a space velocity of 571 mL·gcat –1·h–1. Based on operando spectroscopic studies, the striking activity of this Cu-based catalyst is ascribed to the stabilization of Cu+ ions favored under reaction conditions due to lattice reorganization associated with the “HT-memory effect” promoted by water. Temperature-resolved infrared–mass spectrometry experiments have enabled the discernment of monodentate formate species, stabilized on Cu+ as the intermediate in methanol synthesis, in line with the results of density functional theory calculations. These monodentate formate species are much more reactive than bridge formate species, the latter ones behaving as intermediates in methane and CO formation. Moreover, poisoning of the Cu0 surface by strongly adsorbed species behaving as spectators is observed under reaction conditions. This work presents a detailed spectroscopic study highlighting the influence of the reaction pressure on the stabilization of active surface sites, and the possibility of enhancing methanol production on usually less active non-promoted nano-sized copper catalysts, provided that the proper support is selected, allowing the stabilization of doped Cu+. Thus, a methanol formation rate of 2.6 × 10–3 molMeOH·gcat –1·h–1 at 230 °C, 20 bar, and WHSV = 28 500 mL·gcat –1·h–1 is obtained on the Cu–MgO–Al2O3 HT-derived catalyst with 71% methanol selectivity, compared to 2.2 × 10–4 molMeOH·gcat –1·h–1 with 54% methanol selectivity obtained on a reference Cu/(Al2O3/MgO) catalyst not derived from a HT structure.

The dynamic behavior of a CuO/ZnO/Ga2O3 catalyst under Methanol Steam Reforming (MSR) reaction conditions promoted by a high dispersion of the copper nanoparticles and defect sites of a non-stoichiometric ZnGa2O4 spinel phase has been observed, where structural changes taking place in the initial state of the reaction determine the final state of the catalyst in stationary reaction conditions. Mass Spectrometry (MS) studies under transient conditions coupled to X-Ray Photoelectron Spectroscopy (XPS) have shown copper oxidation to Cu + in the initial state of the reaction (TOS = 4 min), followed by a fast reduction of the outer shell to Cu 0 , while keeping dissolved oxygen species in the inner layers of the nanoparticle. The presence of this subsurface oxygen impairs a positive charge to the uppermost surface copper species, i.e.Cu δ+ , which undoubtedly plays an important role on the MSR catalytic activity. The detection of these features, unperceived by conventional spectroscopic and catalytic studies, has only been possible by combining synchrotron NAP-XPS studies with transient studies performed in a low volume catalytic reactor connected to MS and linked with Raman and laboratory scale XPS studies.

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Confined nanosized spaces at the interface between a metal and a seemingly inert material, such as a silicate, have recently been shown to influence the chemistry at the metal surface. In prior work, we observed that a bilayer (BL) silica on Ru(0001) can change the reaction pathway of the water formation reaction (WFR) near room temperature when compared to the bare metal. In this work, we looked at the effect of doping the silicate with Al, resulting in a stoichiometry of Al0.25Si0.75O2. We investigated the kinetics of WFR at elevated H2 pressures and various temperatures under interfacial confinement using ambient pressure X-ray photoelectron spectroscopy. The apparent activation energy was lower than that on bare Ru(0001) but higher than that on the BL-silica/Ru(0001). The apparent reaction order with respect to H2 was also determined. The increased residence time of water at the surface, resulting from the presence of the BL-aluminosilicate (and its subsequent electrostatic stabilization), favors the so-called disproportionation reaction pathway (*H2O + *O ↔ 2 *OH), but with a higher energy barrier than for pure BL-silica.