Dicalcium silicate (C2S) is known to incorporate potentially hazardous metals (Cr and V) in a belite-rich cementitious system. The effect of the electrovalence nature of V and Cr on C2S polymorphs' (α´, β, γ) stability under oxidizing and reducing conditions as well as their reactivity are systematically investigated via analyzing oxidation states, phase composition, bonding system, and microstructure as well as oxide composition quantitively. It is shown that C2S can incorporate Cr (VI) and V(V) consequently leading to stabilization of α´, β-C2S. Instead, Cr (II, III) and V < (V) tend not to substitute in C2S. Despite reactive polymorphs (α´, β-C2S) stability due to Cr (VI) and V(V) incorporation, the early age (48-72 h) C2S reactivity is drastically reduced due to Cr (VI) and V (V) incorporation. Moreover, one batch leaching test revealed that the V (V) leaching is inversely proportional to aqueous Ca2+ ion at pH > 12 while Cr leaching is sensitive to its oxidation state, and dissolution of C2S. Even though C2S can incorporate Cr (VI) and V (V) ions, the final leaching is governed by the immobilization potential of C-S-H gel, pH as well as types of calcium chromate and vanadate complexes.

The influence of the support-oxygen groups and Pt particle size on the catalytic performance of Pt/AC for the aerobic oxidation of alpha-D-glucose to gluconic acid (glycolate) was studied. Surface-oxygen groups were introduced by treating the activated carbon support with diluted HNO3 without significantly affecting the support porosity. The platinum particle size could be decreased on both the treated and untreated support by adding an additional calcination step to the synthesis. The presence of oxygen-containing groups is shown to be highly beneficial (similar to 4 fold increase in the turnover frequency) only for the smallest Pt particle size (1.8-2.5 nm, determined by TEM). For the catalyst with the larger Pt size (3.4-3.6 nm), the presence of additional oxygen-contacting groups does not significantly enhance the activity. Since the size of the smaller Pt particles is close to the product/substrate molecular diameter (glucose/gluconic acid, similar to 0.9 nm) the observed effect can be attributed to the effective repulsion by the negatively charged oxygen groups in close proximity to the glycolate reaction product. The increase in activity originates from the resulting enhanced desorption of glycolate by alleviating the product inhibition presence due to the strong interaction of glycolate with Pt.

Hydrogenation of levulinic acid to gamma-valerolactone is a key reaction in the valorization of carbohydrates to renewable fuels and chemicals. State-of-the-art catalysts are based on supported noble metal nanoparticle catalysts. We report the utility of a bimetallic Fe-Re supported on TiO2 for this reaction. A strong synergy was observed between Fe and Re for the hydrogenation of levulinic acid in water under mild conditions. Fe-Re/TiO2 shows superior catalytic performance compared to monometallic Fe and Re catalysts at similar metal content. The hydrogenation activity of the bimetallic catalysts increased with Re content. H-2-TPR, XPS, XANES, EXAFS, Mossbauer spectroscopy, TEM, and low-temperature CO IR spectroscopy show that the bimetallic catalysts contain metallic Re nanoparticles covered by FeOx species and small amounts of a Fe-Re alloy. Under reaction conditions, the partially reduced surface FeOx species adsorb water and form Bronsted acidic OH groups, which are involved in dehydration of reaction intermediates. Under optimized conditions, nearly full conversion of levulinic acid with a 95 % yield of gamma-valerolactone could be achieved at a temperature as low as 180 degrees C in water at a H-2 pressure of 40 bar.

Based on previous work that identified iridium(III) Cp* complexes containing a C,N-bidentate chelating triazolylidene-pyridyl ligand (Cp* = pentamethylcyclopentadienyl, C 5Me 5 –) as efficient molecular water oxidation catalysts, a series of new complexes based on this motif has been designed and synthesized in order to improve catalytic activity. Modifications include specifically the introduction of electron-donating substituents into the pyridyl unit of the chelating ligand (H, a; 5-OMe, b; 4-OMe, c; 4-tBu, d; 4-NMe 2, e), as well as electronically active substituents on the triazolylidene C4 position (H, 8; COOEt, 9; OEt, 10; OH, 11; COOH, 12). Chemical oxidation using cerium ammonium nitrate (CAN) indicates a clear structure-activity relationship with electron-donating groups enhancing catalytic turnover frequency, especially when the donor substituent is positioned on the triazolylidene ligand fragment (TOF max = 2500 h – 1 for complex 10 with a MeO group on pyr and a OEt-substituted triazolylidene, compared to 700 h – 1 for the parent benchmark complex without substituents). Electrochemical water oxidation does not follow the same trend, and reveals that complex 8b without a substituent on the triazolylidene fragment outperforms complex 10 by a factor of 5, while in CAN-mediated chemical water oxidation, complex 10 is twice more active than 8b. This discrepancy in catalytic activity is remarkable and indicates that caution is needed when benchmarking iridium water oxidation catalysts with chemical oxidants, especially when considering that application in a potential device will most likely involve electrocatalytic water oxidation.

The Cover Feature shows how molybdenum leaches from the nickel-molybdenum electrocatalysts used for the hydrogen evolution reaction. Molybdenum leaching primarily occurs under the influence of hydroxyl anions, but it is also a function of the counter cation (e.g. Na+, K+, and Li+) used during electrocatalysis. The accompanied increase of the catalyst surface area results in an increased electrocatalytic efficiency. More information can be found in the Full Paper by J. H. J. Wijten et al.

A new, sustainable catalytic route for the synthesis of tetrahydrofuran-2,5-dicarboxylic acid (THFDCA), a compound with potential application in polymer industry, is presented starting from the bio-based platform chemical 5-(hydroxymethyl)furfural (HMF). This conversion was successfully achieved via oxidation of tetrahydrofuran-2,5-dimethanol (THFDM) over hydrotalcite (HT)-supported gold nanoparticle catalysts (∼2 wt %) in water. THFDM was readily obtained with high yield (>99%) from HMF at a demonstrated 20 g scale by catalytic hydrogenation. The highest yield of THFDCA (91%) was achieved after 7 h at 110 °C under 30 bar air pressure and without addition of a homogeneous base. Additionally, Au–Cu bimetallic catalysts supported on HT were prepared and showed enhanced activity at lower temperature compared to the monometallic gold catalysts. In addition to THFDCA, the intermediate oxidation product with one alcohol and one carboxylic acid group (5-hydroxymethyl tetrahydrofuran-2-carboxylic acid, THFCA) was...

The catalytic activity of metal nanoparticles can be altered by applying strain, which changes the crystalline lattice spacing and modifies the electronic properties of the metal. Understanding the role of elastic strain during catalytic reactions is thus crucial for catalyst design. Here, we show how single highly faceted Pt nanoparticles expand or contract upon interaction with different gas atmospheres using in situ nano-focused coherent X-ray diffraction imaging. We also demonstrate inter-particle heterogeneities, as they differ in development of strain under CO oxidation reaction conditions. The reported observations offer new insights into the design of catalysts exploiting strain effects.

The role of aluminum in the structure of hydrotalcite-based sorbents was investigated with Al-27-NMR and XPS with respect to the chemisorption mechanism of different sorbate species, such as CO2, H2O and H2S, at elevated temperatures. Sorbent materials with different ratios of Al/Mg were studied in order to elucidate the influence of the material composition on the Al coordination. Two different tetrahedrally and octahedrally coordinated Al species were detected. It was found that their quantitative appearance depends on the ratio of Al/Mg within the sorbent material. A higher Mg content leads to a higher distortion and to the formation of more tetrahedrally coordinated Al with a high chemical shift. Whereas CO2 and H2O adsorption does not seem to influence well-coordinated Al, as observed with NMR, chemisorption of H2S showed a clear interaction with Al leading to the formation of an additional tetrahedrally coordinated site with a high chemical shift. XPS showed that a reversible metal sulfate complex was formed on the sorbent, which was reversible upon exposure to H2O. (C) 2019 The Authors. Published by Elsevier Ltd.

The activation processes of [Cu-II(bdmpza)(2)] in the water oxidation reaction were investigated using cyclic voltammetry and chronoamperometry. Two different paths wherein CuO is formed were distinguished. [Cu-II (bdmpza)(2)] can be oxidized at high potentials to form CuO, which was observed by a slight increase in catalytic current over time. When [Cu-II(bdmpza)(2)] is initially reduced at low potentials, a more active water oxidation catalyst is generated, yielding high catalytic currents from the moment a sufficient potential is applied. This work highlights the importance of catalyst pre-treatment and the choice of the experimental conditions in water oxidation catalysis using copper complexes. (C) 2016 Published by Elsevier B.V.

The addition of Re to Ni on TiO2 yields efficient catalysts for the hydrogenation of acids and esters to alcohols under mild conditions. Rhenium promotes the formation of atomically dispersed and sub-nanometre-sized bimetallic species interacting strongly with the oxide support.

Here we showcase the synthesis and catalytic response of the anionic iridium(III) complex [IrCl3(pic)(MeOH)]− ([1]−, pic = picolinate) toward the evolution of oxygen. Online electrochemical mass spectrometry experiments illustrate that an initial burst of CO2 due to catalyst degradation is expelled before the oxygen evolution reaction commences. Electrochemical features and XPS analysis illustrate the presence of iridium oxide, which is the true active species.

The effect of Re-addition to Pt/TiO2 catalysts for the hydrogenation of carboxylic acids and esters to their corresponding alcohols was investigated. The highest catalytic activity was observed for the materials with Pt:Re molar ratio of 1:2, which allowed for a complete conversion of hexanoic acid under mild conditions. The hydrogenation of esters over the same catalysts was much more difficult. The reactions showed only moderate alcohol yields which also depended strongly on the alkoxy moiety of the ester substrate. The highest yield of ca. 25% was achieved by the hydrogenation of ethyl hexanoate. Conversion of methyl hexanoate was much less efficient. This was attributed to the inhibiting effect of methanol byproduct. In situ FTIR spectroscopy suggests that the decarbonylation of methanol and the resulting CO poisoning of the catalyst surface in the course of the reaction is the most likely cause of the low activity of Pt and Pt-Re/TiO2 towards methyl ester hydrogenation. (C) 2016 Elsevier B.V. All rights reserved.

When exposed to a potential exceeding 1.5 V versus RHE for several minutes the molecular iridium bishydroxide complex bearing a pentamethylcyclopentadienyl and a N-dimethylimidazolin-2-ylidene ligand spontaneously adsorbs onto the surface of glassy carbon and gold electrodes. Simultaneously with the adsorption of the material on the electrode, the evolution of dioxygen is detected and modifications of the catalyst structure are observed. XPS and XAS studies reveal that the species present at the electrode interface is best described as a partly oxidized molecular species rather than the formation of large aggregates of iridium oxide. These findings are in line with the unique kinetic profile of the parent complex in the water oxidation reaction.

Plasma-assisted atomic layer deposition (PA-ALD) was adopted to deposit TiO2-xNx ultrathin layers on Si wafers, calcined Ti foils and nanotubular TiO2 arrays. A range of N content and chemical bond configurations were obtained by varying the background gas (O-2 or N-2) during the Ti precursor exposure, while the N-2/H-2-fed inductively coupled plasma exposure time was varied between 2 and 20s. On calcined Ti foils, a positive effect from N doping on photocurrent density was observed when O-2 was the background gas with a short plasma exposure time (5 and 10 s). This correlates with the presence of interstitial N states in the TiO2 with a binding energy of 400 eV (N-interst) as measured by X-ray photoelectron spectroscopy. A longer plasma time or the use of N-2 as background gas results in formation of N state with a binding energy of 396 eV (N-subst) and very ow photocurrents. These N-subst are linked to the presence of Ti3+, which act as detrimental recombination center for photo-generated electron-hole pairs. On contrary, PA-ALD treated nanotubular TiO2 arrays show no variation of photocurrent density (with respect to the pristine nanotubes) upon different plasma exposure times and when the O-2 recipe was adopted. This is attributed to constant N content in the PA-ALD TiO2-xNx, regardless of the adopted recipe. (C) 2015 Elsevier B.V. All rights reserved.

A novel catalyst material for the selective dehydrogenation of propane is presented. The catalyst consists of 1000 ppm Pt, 3 wt% Ga, and 0.25 wt% K supported on alumina. We observed a synergy between Ga and Pt, resulting in a highly active and stable catalyst. Additionally, we propose a bifunctional active phase, in which coordinately unsaturated Ga3+ species are the active species and where Pt functions as a promoter.

Mixed Ga-Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and solid-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photocatalytic water splitting, CO oxidation, and H-2 oxidation. Mixed Ga-Zn oxynitrides produced by wet precipitation and nitridation had good visible-light-absorption properties and high surface areas, so they were used to support uniformly sized poly(vinylpyrrolidone)-stabilized Rh nanoparticles. The nanoparticle size range was 2-9 nm. These catalysts had negligible activity in photocatalytic H-2 production by water splitting with methanol as a sacrificial agent. Other mixed Ga-Zn oxynitrides were also inactive. A reference sample provided by Domen also showed very low activity. The influence of particle size on Rh-catalyzed oxidation of CO and H-2 was investigated. For CO oxidation, the activities of small particles were higher for particles with higher Rh oxidation degrees. The opposite holds for H-2 oxidation. (C) 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Enhanced productivity toward propene oxide in the direct propene epoxidation with hydrogen and oxygen over gold nanoparticles supported on titanium‐grafted silica was achieved by adjusting the gold–titanium synergy. Highly isolated titanium sites were obtained by lowering the titanium loading grafted on silica. The tetrahedrally coordinated titanium sites were found to be favorable for attaining small gold nanoparticles and thus a high dispersion of gold. The improved productivity of propene oxide can be attributed to the increased amount of the interfacial AuTi sites. The active hydroperoxy intermediate is competitively consumed by epoxidation and hydrogenation at the AuTi interface. A higher propene concentration is favorable for a lower water formation rate and a higher formation rate of propene oxide. Propene hydrogenation, if occurring, can be switched off by a small amount of carbon monoxide.

Unraveling the oxidation state of gold is important to understand the role of gold in direct propene epoxidation on gold–titania catalysts. A Fourier transform infrared study of low-temperature carbon monoxide adsorption was performed over Au/TiO2 and Au/Ti–SiO2 under an atmosphere of the reaction mixture of oxygen, hydrogen, and propene. Data reveals that the active gold sites treated by the reaction mixture are fully covered by reaction intermediates and deactivating species. Oxidation at 573 K removes these carbonaceous species on gold. Oxygen adsorption at the reaction temperature leads to positively charged gold, which can be reduced to metallic gold in the presence of hydrogen. Propene acts as an electron donor to the gold atoms resulting in negatively charged gold with the carbonyl band at 2079 cm−1. The results in this study may provide a general scheme of electron transfer via gold on the gold–titania catalysts for direct propene epoxidation.

In this paper we report a study of novel thermally stable surface enhanced Raman scattering (SERS) substrates consisting of Ag nanoparticles immobilized on an anodized aluminum oxide (AAO) support. The morphological and chemical characteristics and the SERS activity of the Ag nanoparticles before and after the thermal treatment were evaluated using SEM, XPS, UV-vis and Raman spectroscopy. Our results show that the nanoporous surface of AAO significantly hinders the fusion of Ag nanoparticles to single large particles at up to 400 degrees C, preserving high SERS enhancement. XPS and SERS results indicate that exposure to high temperatures efficiently 'cleanses' the surface from citrate remnants, opening more binding sites for analytes on Ag nanoparticles. In addition, thermal decomposition of silver oxide occurs at 400 degrees C, ensuring a pure metallic surface and further enhancing SERS activity.

Aerobic oxidation of a thin film of octadecanol at 105°C and ambient pressures to its corresponding carbonyl derivatives (a mixture of aldehyde and carboxylic acid) was for the first time performed over a flat-model (i.e. two-dimensional), silicon wafer-supported metallic silver catalyst. The experimental set-up was extraordinary simple. An open-to-the-atmosphere glass beaker was used as reactor. Just enough octadecanol was placed on the silicon-supported catalytic surface to cover it with a thin film when melted. Reaction progress was monitored by ATR-FTIR analyses to identify the appearance of octadecanal and octadecanoic acid carbonyl stretching peaks at 1730 and 1710cm−1 respectively. The successful demonstration of this simple approach in studying catalysed small-molecule condensed organic reactions opens a new avenue towards simplified catalytic mechanistic studies of such processes. The catalyst was prepared by spin coating silver nitrate on a flat silicon wafer with (100) surface orientation, pretreated to have 4−5 silanol (SiOH) groups per nm2. Reduction by hydrogen at 350°C afforded metallic silver particles on the two-dimensional support at a nominal surface concentration of ca. 21–23 silver atoms/nm2. XPS differentiation between the catalyst precursor, AgNO3, and the metallic silver catalytic surface required use of the Auger MNN kinetic energies. TEM studies of the active catalyst showed no serious aggregation of metallic Ag particles occurred during reduction.