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We present a multifunctional structural coloration strategy for solar cell glass covers based on all-dielectric nanoscatterer arrays. Titanium dioxide (TiO2) nanostructures are designed to efficiently scatter in the visible and absorb in the UV region, making them suitable candidates as UV absorptive color coatings. Results from finite difference time domain (FDTD) simulations on a square lattice of TiO2 nanocylinders show that a rich palette in the reflected colors can be obtained by varying the period of the lattice. The reflected colors are narrow-banded, with a typical FWHM similar to 11-17 nm, leading to a minimal penalty on the amount of transmitted light. This narrow band reflectance is attributed to the interaction of Mie resonances between individual scatterers with their neighbors in the lattice. The color appearance, with viewing angles of similar to 45 degrees, is maintained for incidence angles up to similar to 70 degrees. With TiO2 being transparent for a major part of silicon solar cells spectral response (400-1100 nm), a loss of similar to 4.5-9.2% in the short-circuit current has been estimated in the specified wavelength range, primarily due to the loss of photons in the reflected light. Furthermore, due to the inherent UV-absorption properties of TiO2, the proposed color-cover designs reduce the transmittance of UV radiation (320-400 nm) by up to similar to 63.70%, potentially preventing the degradation of the encapsulation materials and thus increasing the lifetime expectancy of a solar panel., QC 20220610

The main objective of this research is a systematic development of advanced micro/nanostructured materials based on most used metal-oxides for ORR and metal-oxide with extremely low-loading of Pt for comparison. Hybrid composites that were compared are: MnO2, La2O3, LMO and LMO-Pt. The influence of reduced amount of noble metal, as well as single oxide activity toward ORR was analyzed. The complete electrochemical performances of the hybirde materials have been done by means of CV, LSV and EIS.

The rational design of catalysts by tailoring specific surface sites with different elements could result in catalysts with high activity, selectivity, and stability. In this work, we show that *CO on-top and O* on-top adsorption energies are good descriptors for the catalysis of the CO oxidation reaction (COOR) on pure metals and binary alloys. The observed Bronsted-Evans- Polanyi (BEP) and scaling relations for the COOR on different surfaces are incorporated into a predictive model that uses the binding strength of the four adjacent metal atoms making up the active site for COOR catalysis to estimate reaction and activation energies. The model is used to screen 161 multimetallic catalyst candidates made by combining Ru, Pt, Pd, Cu, and Au at these four sites. The screening and subsequent calculations suggest that Ru-Pt-Cu alloys are good catalysts for the COOR. Our study shows that it is possible to use information from pure metals and binary alloys to predict the catalytic behavior of more complex alloys, and hereby reduce the computational cost of identifying catalyst candidates for COOR.

A novel hybrid solvothermal approach for perovskite nanocrystal formation via accurate control of the hydrolytic process is reported. This new synthetic methodology sets a whole general route to successfully tune the sizes of high-quality BaMO3 (M = Ti4+, Zr4+, and Hf4+) perovskite nanocrystals. Purely cubic-phase nanocrystals (stable in alcohol media) were obtained using controlled water amounts, combining the well-known aqueous sol–gel process with the classic solvothermal method. Exhaustive optimizations revealed feasibility of a fast (1 hour) and reproducible synthesis with small variations in the crystal size or agglomeration parameters. The study also reveals water content as the pivotal factor to achieve this wide range of sizes through a controlled hydrolytic step. Finally, the study of the hydrolytic process made it possible to shed some light on mechanistic insights of this synthetic route.

A sustainable future requires clean energy and environmental technologies. At the heart of these technologies are high-performance catalysts that efficiently increase the rate and selectivity of key chemical reactions involved. Single perovskites have long been considered as a class of active catalysts with a relatively simple atomic arrangement. Double perovskites, a subclass of perovskites characterized by cation ordering, are emerging alternatives to single perovskites showing comparable or even better performance. In this review, we explore recent developments of double perovskites in various catalytic applications including general catalysis, electrocatalysis, and photo(electro)catalysis. We also discuss how double perovskite chemistries can be tailored toward improved functionality and identify opportunities for the future research of double perovskite catalysts.

A comparative study of the electrochemical intercalation of Ca2+ and Mg2+ in layered TiS2 using alkylcarbonate-based electrolytes is reported, and for the first time, reversible electrochemical Ca2+ insertion is proved in this compound using both X-ray diffraction and differential absorption X-ray tomography at the Ca L-2 edge. Different new phases are formed upon M2+ insertion that are structurally characterized, their amount and composition being dependent on M2+ and the experimental conditions. The first phase formed upon reduction is found to be the result of an ion-solvated intercalation mechanism, with solvent molecule(s) being cointercalated with the M2+ cation. Upon further reduction, new non-cointercalated calcium-containing phases seem to form at the expense of unreacted TiS2. The calculated activation energy barriers for Ca2+ migration in TiS2 (0.75 eV) are lower than those previously reported for Mg (1.14 eV) at the dilute limit and within the CdI2 structural type. DFT results indicate that the expansion of the interlayer space lowers the energy barrier and favors a different pathway for Ca2+ migration., Ministerio de Economia y Competitividad (España), Toyota Motor Europe, Ministerio de Ciencia e Innovación (España), Depto. de Física de Materiales, Depto. de Química Inorgánica, Instituto Pluridisciplinar (IP), Fac. de Ciencias Físicas, Fac. de Ciencias Químicas, TRUE, pub

The active combustion catalyst that is based on 30 wt % cobalt oxide on mesoporous SBA-15 has been tested in 1,2-dichloropropane oxidation and is characterized by means of FT-IR (Fourier transform infrared spectroscopy) and ammonia-TPD (temperature-programmed desorption). In this work, we report the spectroscopic evidence for the role of surface acidity in chloroalkane conversion. Both Lewis acidity and weakly acidic silanol groups from SBA support are involved in the adsorption and initial conversion steps. Moreover, total oxidation reaction results in the formation of new Bronsted acidic sites, which are likely associated with the generation of HCl at high temperature and its adsorption at the catalyst surface. Highly dispersed Co oxide on the mesoporous support and Co-chloride or oxychloride particles, together with the presence of several families of acidic sites originated from the conditioning effect of reaction products may explain the good activity of this catalyst in the oxidation of Chlorinated Volatile Organic Compounds.

The active combustion catalyst that is based on 30 wt % cobalt oxide on mesoporous SBA-15 has been tested in 1,2-dichloropropane oxidation and is characterized by means of FT-IR (Fourier transform infrared spectroscopy) and ammonia-TPD (temperature-programmed desorption). In this work, we report the spectroscopic evidence for the role of surface acidity in chloroalkane conversion. Both Lewis acidity and weakly acidic silanol groups from SBA support are involved in the adsorption and initial conversion steps. Moreover, total oxidation reaction results in the formation of new Bronsted acidic sites, which are likely associated with the generation of HCl at high temperature and its adsorption at the catalyst surface. Highly dispersed Co oxide on the mesoporous support and Co-chloride or oxychloride particles, together with the presence of several families of acidic sites originated from the conditioning effect of reaction products may explain the good activity of this catalyst in the oxidation of Chlorinated Volatile Organic Compounds.

The active combustion catalyst that is based on 30 wt % cobalt oxide on mesoporous SBA-15 has been tested in 1,2-dichloropropane oxidation and is characterized by means of FT-IR (Fourier transform infrared spectroscopy) and ammonia-TPD (temperature-programmed desorption). In this work, we report the spectroscopic evidence for the role of surface acidity in chloroalkane conversion. Both Lewis acidity and weakly acidic silanol groups from SBA support are involved in the adsorption and initial conversion steps. Moreover, total oxidation reaction results in the formation of new Bronsted acidic sites, which are likely associated with the generation of HCl at high temperature and its adsorption at the catalyst surface. Highly dispersed Co oxide on the mesoporous support and Co-chloride or oxychloride particles, together with the presence of several families of acidic sites originated from the conditioning effect of reaction products may explain the good activity of this catalyst in the oxidation of Chlorinated Volatile Organic Compounds.

peer-reviewed, Catalysts with about 2.5 wt% of gold supported on Al2O3, ZrO2, CeO2, La2O3 and MgO oxides and with the same mean metal particle sizes of 2.4-3.0 nm have been studied in hydrogen production via formic acid decomposition. A strong volcano-type relation of the catalytic activity on the electronegativity of the support's cation was demonstrated with the Au/Al2O3 catalyst on the top. This indicated that the activity is affected by the acid-base properties of the support. A study of the most active Au/Al2O3 catalyst with aberration-corrected HAADF/STEM, XPS and EXAFS proved that gold is in metallic state. The content of single supported gold atoms/cations was negligible. Therefore, the mechanism of the reaction was related to the activation of formic acid on the catalyst's support followed by further decomposition of the formed reaction intermediate on the Au/support interface., PUBLISHED, peer-reviewed

A new subporphyrin was synthesized for use as a molecular sensitizer in electrochemical and dye-sensitized photoelectrochemical water oxidation. A photoelectrochemical cell with a TiO2 electrode modified with the sensitizer and a molecular water oxidation catalyst generated higher photocurrent than reference cells that have electrodes modified with either the photosensitizer or the catalyst under visible light (lambda > 500 nm) illumination. Oxygen evolution was confirmed after photolysis by GC and GC-MS analyses using isotope-labeling experiments. The large molar extinction coefficients of the ring-contracted porphyrin in the visible region enabled kinetic analysis by time-resolved transient absorption spectroscopy, which also supported the photocatalytic activity., QC 20170109

The Lebedev ethanol-to-butadiene process entails a complex chain of reactions that require catalysts to possess a subtle balance in the number and strength of acidic and basic sites. SiO2-MgO materials can be excellent Lebedev catalysts if properly prepared, as catalyst performance has been found to depend significantly on the synthesis method. To assess the specific requirements for butadiene production in terms of active sites and to link their presence to the specific preparation method applied, five distinct SiO2-MgO catalysts, prepared by wet-kneading and co-precipitation methods, were thoroughly characterized. The amount and strength of the acidic (pyridine-IR and NH3-TPD) and basic (CDCl3-IR and CO2-TPD) sites of the materials as well as the overall acid/base properties in the liquid phase (Hammett indicators) were determined. The number of acidic and strong basic sites could be correlated with the extent of ethylene and diethyl ether by-product formation. The best performing catalysts are those containing a small amount of strong basic sites, combined with an intermediate amount of acidic sites and weak basic ones. These results thus provide further insight into the relation between the amount and strength of acidic/basic sites, preparation method and catalytic performance.

Dehydrogenation promoters greatly enhance the performance of SiO2-MgO catalysts in the Lebedev process. Here, the effect of preparation method and order of addition of Cu on the structure and performance of Cu-promoted SiO2-MgO materials is detailed. Addition of Cu to MgO via incipient wetness impregnation (IWI) or coprecipitation (CP) prior to wet-kneading with SiO2 gave similar butadiene yields (similar to 40%) as when Cu was added to the already wet-kneaded catalyst. In contrast, the catalyst prepared by impregnation of Cu on SiO2 first proved to be the worst catalyst of the series. TEM, XRD, and XPS analyses suggested that, for all catalyst materials, Cu2+ forms a solid solution with MgO. This was confirmed by UV-vis, XANES, and EXAFS data, with Cu being found in a distorted octahedral geometry. As a result, the acid base properties, as determined by Pyridine- and CDCl3-IR as well as NH3-TPD, are modified, contributing to the improved performance. Operando XANES and EXAFS studies of the evolution of the copper species showed that Cu2+, the only species initially present, is extensively reduced to a mixture of Cu-0 and Cu+, leaving only a limited amount of unreduced Cu2+. This formation of Cu-0 is the result of the reducing environment of the Lebedev process and is thought to be mainly responsible for the improved performance of the Cu-promoted catalysts.

We report on the solar-light-mediated degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on hematite and goethite nanoparticles in synthetic air. Adsorption and photoreactions of TMP and TEP were studied by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) on dry and water-precovered nanoparticles in dark and under simulated solar light irradiation. Two-dimensional correlation analysis of infrared spectra was used to identify surface products as a function of reaction time. The optical properties of the hematite and goethite nanoparticles were investigated with optical spectrophotometry. The optical band gap was determined by analysis of the Tauc relationship around the band gap energy, E-g, yielding band gap energies of 2.14 and 2.28 eV for hematite and goethite nanoparticles, respectively. It is found that both TMP and TEP are readily photodegraded upon solar light irradiation (employing AM1.5 filters with 1735 W m(-2)), yielding surface orthophosphate as the final product. The first step in the dissociation of TMP and TEP is displacement of the methoxy and ethoxy groups, respectively, yielding adsorbed dimethyl phosphate (DMP) and methoxy, and diethyl phosphate (DEP) and ethoxy intermediates. Further photodegradation displaces additional methoxy and ethoxy groups with adsorbed orthophosphate as final reaction product. Methoxy and ethoxy fragments are simultaneously oxidized to carboxylates and carbonates. Photodegradation of TMP and TEP is promoted by OH radicals, which is evidenced by the higher photodegradation rate on water-precovered surfaces. The rate of TMP degradation is higher than that for TEP contrary to what is expected from their corresponding bulk hydrolysis rates, but consistent with their surface reactivity in dark, where TMP is observed to dissociate at room temperature but not TEP (or only very slowly). The photodegradation rate is higher on the goethite nanoparticles than the hematite nanoparticles o

An ultrahigh vacuum technique using mass spectrometry for in-situ investigations of gas-solid interactions is described in this paper. Examples of chemical reactions (oxidation, hydration) between solids and gas mixtures, dissociation of gases on solid surfaces, outgassing of solid materials and permeation of gases through membranes are discussed where the experimental arrangement is explained in detail. This Gas Phase Analysis (GPA) technique can be used at temperatures from room temperature to 1200 degrees C and at pressures up to 1 atm. Aspects related to sample preparation, isotopic gas mixture selection, data acquisition, calibration and interpretation of the experimental data are also addressed., Conference: Workshop on Size-dependent Effects in Materials for Environmental Protection and Energy Application. Varna, BULGARIA. MAY 25-27, 2006

The efficiency of dilute oxalic and citric acid solutions on improving the oxygen storage capacity (OSC) and catalytic activity of a severely aged (83 000 km) commercial three-way catalyst (TWC) has been investigated. Washing procedures applied after optimization of experimental parameters, namely, temperature, flow-rate, and concentration of acid solution, led to significant improvements of OSC and catalytic activity (based on dynamometer test measurements) of the aged TWC. The latter was made possible due to the removal of significant amounts of various contaminants accumulated on the catalyst surface (e.g., P, S, Pb, Ca, Zn, Si, Fe, Cu, and Ni) during driving conditions, as revealed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and X-ray Photoelectron Spectroscopy (XPS) analyses. For the first time, it is demonstrated that dilute oxalic acid solution significantly improves the catalytic activity of an aged commercial TWC toward CO, CxHy, and NOx conversions under real exhaust gas conditions (dynamometer tests) by two to eight times in the 250-450 degrees C range and the OSC quantity by up to 50%. Oxalic acid appears to be more efficient than citric acid in removing specifically P- and S-containing compounds from the catalyst surface, whereas citric acid in removing Pb- and Zn-containing compounds, thus uncovering surface active catalytic sites., QC 20100812

Titanium dioxide solution was prepared via sol-gel process with and without acetyl acetone (AcAc). The formation of the anatase phase in the thin films using AcAc was initiated at 300 degrees C while the anatase phase in the thin films without using AcAc began to appear at 100 degrees C. Surface roughness of the TiO2 films using and without using AcAc ranged from 0.414 to 3.08 nm and from 3.72 to 5.35 nm, respectively. Photocatalytic decomposition rate examined by methylene blue solution showed 80% at 400 degrees C and 88% at 600 degrees C for the TiO2 thin films using AcAc. On the other hand, the photocatalytic decomposition rate of the TiO2 thin films without using AcAc showed 80% at 100 degrees C and 97% at 400 degrees C, respectively. At the temperature above 400 degrees C, the photocatalytic activity decreased due to appearance of the rutile phase. Comparison between the TiO2 thin films showing the maximum photocatalytic activity revealed that the TiO2 thin film without using AcAc showed 10% higher photocatalytic decomposition rate from the initial 10 to 120 min as compared with the TiO2 thin film using AcAc, which was closely related to the formation of the anatase phase and the surface roughness., QC 20100525

The relative activities of a low-surface crystalline and high-surface amorphous LaOC1, further denoted as S1 and S2, have been compared for the destructive adsorption of CCl4. It was found that the intrinsic activity of S2 is higher than that of S1. Both samples were characterized with X-ray diffraction (XRD), X-ray pbotoelectron spectroscopy (XPS), N-2-physisorption, and Raman and infrared (IR) spectroscopy. IR was used in combination with CO2, CO, and methanol as probe molecules. The CO2 experiments showed that different carbonate species are formed on both materials. For S1, a high surface concentration of bidentate carbonate species and a lower concentration of monodentate carbonate were observed. In the case of S2, bulk carbonates were present together with bridged carbonates. CO adsorption shows that S2 and S I have very similar Lewis acid sites. However, methanol adsorption experiments showed that S2 had a higher number of stronger Lewis acid sites than S1 and that twofold coordinated methoxy species were more strongly bound than threefold coordinated methoxy species. Because of the analogy between methanol dissociation and the removal of the first chlorine atom in the destructive adsorption Of CCl4, the sites enabling twofold coordination were likely to be the same Lewis acid sites actively involved in the destructive adsorption Of CCl4. La2O3 was less active than the two LaOCl materials, and therefore, the intrinsic activity of the catalyst increases as the strength of the Lewis acid sites increases. S2 contains more chlorine at the surface than S1, which is expressed by the higher number of sites enabling twofold coordination. Moreover, this explains the difference in destructive adsorption capacity for CCl4 that was observed for the samples S1 and S2. Since LaCl3, being the most acidic phase, is not active for the destructive adsorption Of CCl4, basic oxygen atoms, however, remain needed to stabilize the reaction intermediate CCl3 as La-O-CCl3.

Soils under intensive livestock farming and heavily fertilized with animal manure may have elevated soil phosphorus (P) contents. We determined P desorption kinetics in batch experiments using soils from a pot experiment where grass was cropped on a P-rich noncalcareous sandy soil without P addition, to lower the soil P content. A diffusion model was used to describe P desorption kinetics from a spherical aggregate. The model was calibrated with data from the batch experiments. Simulation results show that in the pot experiment, P desorption from the solid phase of the inner layers was initially far from equilibrium with the rest of the aggregate, but desorption came closer to equilibrium as the soil P content decreased further. A simple tool is presented, referred to as the dynamic bioavailability index (DBI), to determine whether kinetics of P desorption limits plant uptake. This tool is the dimensionless ratio of the modeled maximal diffusive flux from soil aggregates to solution and the plant uptake rate measured in the pot experiment. The DBI was initially much larger than one; the maximal possible P desorption rate exceeded the uptake rate, so uptake was not limited by desorption. The DBI stabilized at a value somewhat larger than one after a while, due to soil transport limitations. This decrease coincided with a large decrease of the P content in the grass to a value (far) below what is considered as optimal; the supply rate of P from soil to the root cannot meet the demand needed for optimal P uptake. The DBI could be seen as a promising onset to a new dynamic approach of bioavailability.

The mechanism of catalytic oxidation reactions was studied using in situ X-ray absorption spectroscopy (XAFS) over a 17.5 wt% V2O5/Al2O3 catalyst, i.e., at reaction temperatures and in the presence of reactants. It was found that X-ray absorption near-edge structure (XANES) is a powerful tool to study changes in the local environment and the oxidation state of the vanadium centres during catalytic oxidation. At 623 K, the catalyst follows the associative mechanism in CO oxidation. XAFS revealed that the Mars-van Krevelen mechanism is operative at 723 K for CO oxidation. The extended X-ray absorption fine structure (EXAFS) results showed that the structure of the supported V2O5 phase consists of monomeric tetrahedral (Al-O)(3)-V=O units after dehydration in air at 623 K. However, the residuals of the EXAFS analysis indicate that an extra contribution has to be accounted for. This contribution probably consists of polymeric vanadate species. The structure remains unchanged during steady-state CO oxidation at 623 and 723 K. Furthermore, when oxygen was removed from the feed at 623 K, no changes in the spectra occurred. However, when oxygen is removed from the feed at 723 K, reduction of the vanadium species was observed, i.e., the vanadyl oxygen atom is removed. The V3+ ion subsequently migrates into the gamma-Al2O3 lattice, where it is positioned at an Al3+ octahedral position. This migration process appears to be reversible; so the (Al-O)(3)-V=O units are thus restored by re-oxidation.