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To meet the requirement of high catalytic efficiency toward the reduction of toxic p-nitrophenol (PNP) to useful p-aminophenol (PAP), we herein report Ru supported on heavily hydrogen-doped semiconductors, specifically Ru/hydrogen molybdenum bronzes (Ru/HxMoO3−y), which is prepared via a facile H-spillover route. Detailed characterization by means of UV-vis-NIR diffuse reflectance, XRD, TEM, and XPS measurements reveals that Ru/HxMoO3−y (100) (100 means the hydrogen reduction temperature (°C)) exhibits strong visible light absorption with a plasmonic peak at around 690 nm, which can be tunable by varying its stoichiometry. Under visible light irradiation, the Ru/HxMoO3−y (100) hybrid displays superior catalytic activity to photocatalytic reduction of PNP relative to that under dark conditions, in which HxMoO3−y acts as electron-donor centres and Ru NPs act as active centres. More importantly, a proposed mechanism for the N–O bond reduction on the Ru/HxMoO3−y hybrid is presented. This study provides a new avenue to design efficient plasmonic metal/semiconductor hybrids for green chemistry. [ABSTRACT FROM AUTHOR]

Silica-based micro-, meso-, macro-porous materials offer attractive routes for designing single-site photocatalysts, supporting semiconducting nanoparticles, anchoring light-responsive metal complexes, and encapsulating metal nanoparticles to drive photochemical reactions by taking advantage of their large surface area, controllable pore channels, remarkable transparency to UV/vis and tailorable physicochemical surface characteristics. This review mainly focuses on the fascinating photocatalytic properties of silica-supported Ti catalysts from single-site catalysts to nanoparticles, their surface-chemistry engineering, such as the hydrophobic modification and synthesis of thin films, and the fabrication of nanocatalysts including morphology controlled plasmonic nanostructures with localized surface plasmon resonance. The hybridization of visible-light responsive metal complexes with porous materials for the construction of functional inorganic–organic supramolecular photocatalysts is also included. In addition, the latest progress in the application of MOFs as excellent hosts for designing photocatalytic systems is described. [ABSTRACT FROM AUTHOR]

Abstract: Although black phosphorus (BP) is an interesting 2D nanosheet material with a high hole mobility, its application in the photocatalytic water oxidation for O2 evolution is not reported yet. Herein the use of BP coupled with a reductive hydroxide, Ni(OH)2, is reported for the first time. The developed photo‐assisted process confirms that the BP XPS measurements confirm that the oxidation state of BP is reduced through the photo‐assisted loading method. The obtained P−Ni(OH)2 samples present the steady and efficient photocatalytic water splitting for O2 generation. Under the simulated sunlight irradiation in 0.1 M Na2S2O4 solution, the O2 generation rate can reach up to 15.7 μmol/(gcatalyst*h) or 224.3 μmol/(gBP*h). The density functional theory (DFT) calculation suggests that the electrons and holes move to surface of BP and Ni(OH)2, respectively. The merit of self‐polarization of P−Ni(OH)2 ensures the stability of BP and achieves the photocatalytic O2 generation from water. [ABSTRACT FROM AUTHOR]

A PdAg-based nanoparticle catalyst supported on the mesoporous silica material, SBA-15, modified with a weakly basic phenylamine functional group has been developed as a dual heterogeneous catalyst for the H2 delivery and H2 storage reactions mediated by formic acid and carbon dioxide. [ABSTRACT FROM AUTHOR]

Stabilize me: A metal oxide host with a trapped unstable {Mo36}‐type polyoxomolybdate guest exhibits independent reduced diamagnetic building blocks and paramagnetic centers (both types with colors other than the dark blue of the Mo centers). The guest in such systems is stabilized especially by a hydrogen‐bond network between the core and the shell. [ABSTRACT FROM AUTHOR]

Stabilisiert: Ein Metalloxid ‐ Wirt mit einem eingeschlossenen instabilen {Mo36} ‐ artigen Polyoxomolybdat ‐ Gast weist reduzierte diamagnetische Bausteine sowie paramagnetische Zentren auf (beide Arten mit anderen Farben als dem Schwarzblau der Mo ‐ Zentren gekennzeichnet). Der Gast in solchen Systemen wird unter anderem durch ein Netzwerk aus Wasserstoffbrücken zwischen dem Kern und der Schale stabilisiert. [ABSTRACT FROM AUTHOR]

Following procedures formerly developed for the preparation of supported heterogeneous catalysts, carbon-coated cobalt nanoparticles dispersed on porous alumina have been prepared by impregnation of γ-AlO with (NH)[Co(EDTA)] and thermal decomposition in inert atmosphere. Below 350 °C, Co(II) ions are complexed in a hexa-coordinated way by the EDTA ligand. The thermal treatment at 400-900 °C leads to the EDTA ligand decomposition and recovering of the support porosity, initially clogged by the impregnated salt. According to X-ray absorption spectroscopy, and due to in situ redox reactions between the organic ligand and Co(II), both oxidic and metallic cobalt phases are formed. Characterisation by transmission electron microscopy, X-ray diffraction and magnetic measurements reveals that an increase in the treatment temperature leads to an increase of the degree of cobalt reduction as well as to a growth of the cobalt metal particles. As a consequence, the samples prepared at 400-700 °C exhibit superparamagnetism and a saturation magnetisation of 1.7-6.5 emu g at room temperature, whilst the sample prepared at 900 °C has a weak coercivity (0.1 kOe) and a saturation magnetisation of 12 emu g. Metal particles are homogeneously dispersed on the support and appear to be protected by carbon; its elimination by a heating in H at 400 °C is demonstrated to cause sintering of the metal particles. The route investigated here can be of interest for obtaining porous magnetic adsorbents or carriers with high magnetic moments and low coercivities, in which the magnetic nanoparticles are protected from chemical aggression and sintering by their coating. [ABSTRACT FROM AUTHOR]

Periodic DFT calculations coupled to a first-principle thermodynamic approach have allowed us to establish a surface phase diagram for the different terminations of the α-Al2O3(1102) surface in various temperature and water pressure conditions. Theoretical results are compared with previous experimental data from the literature. Under a wide range of temperature and water pressure (including ambient conditions) the most stable surface (denoted C2_1H2O in this work) is terminated with singly coordinated hydroxyls on four-fold coordinated aluminium (Al4C-μ1-OH) while most existing surface models are only considering six-fold coordinated surface Al atoms as in the bulk structure of alumina. The presence of more acidic Al4C-μ1-OH sites helps explain the low Point of Zero Charge (PZC) (between 5 and 6) determined from the onset of Mo oxoanions adsorption on (1102) single crystal wafers. It is also postulated that another termination (corresponding to the hydration of the non-polar, stoichiometric surface, stable in dehydrated conditions) may be observed in aqueous solution depending on the surface preparation conditions. [ABSTRACT FROM AUTHOR]

A set of CaO samples was prepared from thermal decomposition of several precursors, leading to very different surface properties. During storage, CaO samples rehydrated quickly but reversibly. Before characterization, the samples were pre-treated at 1023 K under nitrogen flow to obtain CaO as the active phase. Although this pre-treatment led to almost the same specific surface areas for all samples, their basic reactivity levels toward 2-methylbut-3-yn-2-ol conversion were different from one preparation to another. In contrast with the properties of MgO pre-treated at the same temperature, the basic reactivity of CaO correlates neither with the concentration of surface defects (exposing ions in low coordination) determined by photoluminescence nor with the deprotonation ability toward methanol. In order to identify the active sites on CaO pre-treated under nitrogen in the temperature range 673 K–1023 K, OH groups were quantified with 1H NMR: the higher the surface density of OH groups, the higher the basic reactivity. Even after pre-treatment at 1023 K, after which only a few hydroxyls remain, the basic reactivity is governed by the remaining hydroxylation of the surface. The higher reactivity of OH groups of CaO compared to those of Ca(OH)2and MgO is discussed. [ABSTRACT FROM AUTHOR]

EXAFS spectroscopy is shown as a tool of prime importance to probe the formation of metal–oxygen–support bonds and unravel the surface molecular structure in oxide-supported systems through two examples: (i) a molecular metal complex (Ni(ii) bisglycinate) characterized after impregnation and drying on Al2O3, and (ii) a tungsten oxide nanophase characterized after deposition on zirconia and high temperature thermal treatment (tungstated zirconia catalysts, i.e.WOx/ZrO2). Unlike other spectroscopic techniques, EXAFS at the Ni K-edge proves that a modest thermal activation during the impregnation step triggers the grafting of nickel(ii) bisglycinate onto the support: Al next-nearest neighbours are detected when the impregnation is carried out at 60 °C instead of room temperature. Characterization of WOx/ZrO2catalysts shows the presence of W next-nearest neighbours around tungsten, with W–W distances distinctive of edge-shared WO6octahedra only. The WOxoverlayer can thus be described as bidimensional, nanometric slabs of 4 to 5 WO6units on each side. In these slabs, W octahedra are interconnected to form a more condensed structure than the one present in bulk WO3(in which linkage through corners exists). Moreover, EXAFS results conclusively demonstrate that the WOxoverlayer is directly anchored to the ZrO2surface by means of W–O–Zr bonds with a W–Zr distance of 3.14 . [ABSTRACT FROM AUTHOR]

Ti xSiBEA zeolites ( x = 1.5, 3.2 and 5.8 Ti wt%) are prepared by a two-step postsynthesis method involving (1) dealumination of TEABEA zeolite by nitric acid leading to nests of SiO–H groups in vacant T-atom sites and (2) incorporation of Ti into SiBEA zeolite by reacting TiCl4 vapor with those silanol groups. The incorporation of Ti into the SiBEA framework is evidenced by XRD, 29Si MAS NMR, 1H–29Si CP MAS NMR and 1H MAS NMR. DR UV–vis and XPS investigations show that, for low Ti content, mainly framework tetrahedral Ti(IV) ions are present in Ti xSiBEA zeolites. On the basis of XPS data, the quantification of framework tetrahedral Ti(IV) and framework and/or extra-framework octahedral Ti(IV) ions is followed as a function of Ti content. [ABSTRACT FROM AUTHOR]

Differences between the acidic properties of silicoaluminic Pt-containing catalysts and those assessed on their parent supports have been reported in the literature and attributed to the presence of the metal nanoparticles and to their influence on the acid sites. It is shown here that for mesoporous materials containing various types of Al species, an alternative explanation can be proposed. 27Al NMR spectroscopy, FTIR of adsorbed CO and probe catalytic tests suggest the redistribution of aluminium atoms upon contact of the parent support with the aqueous solution containing the Pt precursor. Upon contact with water and thermal treatment, strong and mild Brønsted sites (Si–O(H)–Al) transform into strong Lewis sites (isolated tetracoordinated Al atoms). As a consequence, it may not be straightforward to deduce the acidic properties of metal-containing catalysts supported on Al-containing mesoporous materials from those of the bare support, because the surface species may differ significantly. [ABSTRACT FROM AUTHOR]

The Cu x SiBEA zeolites prepared by a two-step postsynthesis method are active in selective catalytic reduction of NO by ethanol and their catalytic activity is related to the presence of mononuclear Cu(II) species. Zeolite with isolated lattice mononuclear Cu(II) species is active in this reaction with selectivity toward dinitrogen close to 70–90%. [ABSTRACT FROM AUTHOR]

Fe3+–OH groups of a Fe –H –BEA sample prepared by conventional ion-exchange method are characterized by an IR band at 3686–3684 cm−1. They exhibit a weak acidity: upon low-temperature CO adsorption the O–H stretching modes are blue shifted by 100 cm−1 and the respective carbonyl adducts are observed at 2158 cm−1. The Fe3+–OH groups are reduced at room temperature by NO to form Fe2+–NO species and NO+ groups in cationic positions. Desorption of pre-adsorbed NO at temperatures above 373 K regenerates the Fe3+–OH groups. The relation of the Fe3+–OH species to the so-called α-oxygen is discussed. [ABSTRACT FROM AUTHOR]

Ni (7 wt%)/Al2O3 catalysts prepared by decomposition of Ni(II)-ethylenediamine complexes in inert atmosphere initially contain a mixture of metallic and oxidized nickel. X-ray photoelectron spectroscopy shows that after a hydrogen treatment at 500 °C, the system contains more metallic nickel than catalysts prepared from the usual precursor, nickel nitrate. Carbonaceous species resulting from the partial oxidation of ethylenediamine are also eliminated. The catalyst post-treated in hydrogen exhibits a high metallic surface area accessible to reactants and is able to catalyze CO methanation. [ABSTRACT FROM AUTHOR]

V-containing β zeolites were prepared by solid-state reaction between V2O5 and β zeolite. The zeolite structure was analysed by XRD and N2 physisorption. The V speciation was studied by chemical analysis and different spectroscopies (FT-IR, 27Al-NMR, UV-Vis, EPR, photoluminescence). After calcination of V2O5–β zeolite mechanical mixtures at 500°C, three kinds of V species were identified: (i) oligomeric vanadates with octahedral V5+ easily removed by treatment with NH4OAc, (ii) isolated vanadyl (V=O)2+ ions in axially distorted octahedral or square pyramidal environment, interacting with framework and/or extraframework Al nuclei and (iii) isolated V5+ in tetrahedral and octahedral environments, localized in framework defect sites. The amount of the latter species is higher when water vapor is present during calcination and when parent β zeolite contains a high concentration of defect sites generated by a strong acid pretreatment. Isolated V5+ are easily reduced to tetrahedral V4+ or to square pyramidal (V=O)2+. Possible models of the mechanism of formation of V species by solid-state reaction and further reduction are proposed. [ABSTRACT FROM AUTHOR]

When CO2+/ZSM5 catalysts are prepared by solid state exchange between H-ZSM5 and cobalt acetate, CO2+ ions form layered cobalt phyllosilicate at the surface of the zeolite grains, bringing about a reassessment of the chemistry involved in the preparation of catalytic systems by solid state exchange. [ABSTRACT FROM AUTHOR]

Technical improvement of the photoluminescence cell and its coupling to a dynamic vacuum system allow to avoid quenching phenomena. These results in emission spectra of MgO, which are better-resolved and more stable in time, leading to a better characterization of the very reactive oxide ions, i.e., those in low coordination. Apart from a more precise assignment of the spectra, new developments are proposed to evaluate the relative distribution of ions of low coordination. Discrimination of the oxide ions with different coordination numbers is also possible by studying in situ their interaction with propyne as a probe molecule. [ABSTRACT FROM AUTHOR]

VxSiβ catalysts with x = 0.05, 0.2 and 1.75 V wt%, prepared by a two-step post-synthesis method, have been characterised by physical techniques and their photocatalytic reactivity investigated in the decomposition of NO. XRD and diffuse reflectance UV-Vis spectroscopy show that vanadium is incorporated as tetrahedral Vv species, a result confirmed by XANES and EXAFS. Photoluminescence spectra of VxSiβ catalysts show well-resolved vibrational fine structures due to three different kinds of tetrahedral Vv (α, β, γ) species, with different degrees of distortion. Their relative amounts depend on V content and calcination/hydration treatments. Calcined-hydrated V1.75Siβ, calcined V1.75Siβ and calcined V0.05Siβ exhibit mainly the α, γ and β kind of tetrahedral vanadium, respectively. These samples are active in the decomposition of NO under UV-irradiation, leading mainly to N2 and O2. The decomposition of NO is strongly enhanced in presence of propane, leading to higher yield of N2. The latter strongly depends on the distortion of tetrahedral V species. The highest activity is found for the catalyst with tetrahedral V of highest distortion, lowest V=O bond length and biggest lifetime of its excited triplet state. [ABSTRACT FROM AUTHOR]

The basic mechanisms of transition metal complex (TMC) adsorption on oxide surfaces are now well rationalized. In particular, we have proposed earlier a simple classification based on the role of oxide surface groups in adsorption. However, as our knowledge of specific systems progresses, it appears that this picture has to be refined and that partners other than surface groups and metal ions may take an important part in governing adsorption phenomena. All of the ligands of the transition metal complex are important, even those at first sight unaffected by the adsorption reaction. The functional groups of the so-called “spectator” ligands may in fact establish their own interactions with the surface groups, giving rise to the notion of surface/complex interactional complementarity. This idea is illustrated with analogs from homogeneous coordination chemistry, and we discuss two examples from catalyst preparation that suggest that interactional complementarity also plays a role in this field. [ABSTRACT FROM AUTHOR]

H2PtCl6 adsorption on silica and the evolution of the Pt(IV) speciation upon drying and rewetting were studied by 195Pt NMR, UV-visible, and EXAFS spectroscopies. Upon drying at 40 °C, H2PtCl6 forms outer-sphere complexes with silica. At 90 °C, inner-sphere complexes are formed; this grafting is reversible upon rehydration. Each surface Pt(IV) species is characterized by a specific reduction temperature, as evidenced by TPR. [ABSTRACT FROM AUTHOR]

The quenching effect of NO, O2, CO, and N2O on the photoluminescence of Mo6+/SiO2 has been studied at room temperature as a function of gas pressure. Nonlinear plots of the relative photoluminescence intensity I0/I (I0 is the initial intensity under vacuum) vs. pressure of the quenching gases were rationalized assuming that only adsorbed molecules efficiently quench the (Mo5+–O-)* excited state and that the fraction of adsorbed quenching molecules can be determined from the classical Langmuir-type adsorption isotherm. The ratio of the quenching rate constants for NO and CO calculated from the computer best fits of the experimental I0/I–pressure dependence is in agreement with earlier data on the kinetics of the photocatalytic reduction of NO by carbon monoxide on Mo6+/SiO2. [ABSTRACT FROM AUTHOR]

EPR studies using naturally abundant and 95Mo-enriched molybdenum have shown that reduced MoO x/SiO2catalysts with different dispersion of molybdenum provide a unique opportunity for molecular-level investigations of surface phenomena involved in the bonding to and activation of small molecules by oxide surfaces. Different types of electron transfer (ET) processes accompanying the activation of O2and N2O as well as the reactivity of O-and ⋅CH2OH transients with coadsorbed CH3OH and O2, respectively, have been identified. They include nondissociative and dissociative ET, surface intramolecular ET, and electroprotic transformation (ET coupled with proton transfer). In the case of methanol dehydrogenation it was found that if the reaction occurs on the MoO xcluster centers, ET exhibits a complementary character, in contrast to isolated Mo centers where noncomplementary ET accompanied by migration of the hydroxymethyl intermediate is observed. [ABSTRACT FROM AUTHOR]

In calcined and rehydrated VSiß zeolite prepared following a method described earlier, three kinds of tetrahedral VV species can be clearly identified by photoluminescence spectroscopy even at low V content, in contrast to 51V NMR and diffuse reflectance UV-Visible spectroscopies which do not allow them to be distinguished. A comparative study by photoluminescence and 51V NMR spectroscopies leads to the suggestion that there is a correlation between the vibrational energy of the V=O bond and the corresponding chemical shift of the 51V NMR signal. [ABSTRACT FROM AUTHOR]

A dealuminated zeolite β has been contacted with solutions of ammonium metavanadate to incorporate vanadium as tetrahedral V species which are not removed under treatment with aqueous solution of ammonium acetate. The effects of calcination and rehydration on the environment of the V species have been studied by diffuse reflectance UV-visible and 51V NMR. The reducibility of the V species has been followed by TPR and ESR. The dehydroxylation/rehydroxylation process occurring in the β framework upon dehydration/rehydration has been monitored by 29Si MAS NMR and FT-IR spectroscopy. [ABSTRACT FROM AUTHOR]

Presents a study on the nature and strength of the interactions between V species and aluminophosphate molecular sieves. Observations on zeolitic materials; Details on the experiment; Results and conclusion.

The superoxide radical anion O2 - is both an important intermediate in heterogeneous catalytic oxidation and a useful probe for positive charges in ionic solids, such as metal oxides and zeolites. The paper illustrates the main circumstances under which stable superoxide anions are formed at surfaces: (i) direct surface–oxygen electron transfer; (ii) photoinduced electron transfer; (iii) surface intermolecular electron transfer; (iv) decomposition of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Titanium-silicon (Ti/Si) binary oxides having different Ti content were prepared by the sol-gel method and utilized as photocatalysts for the hydrogenation and hydrogenolysis of CH2CCH with H2O. The photocatalytic reactivity and selectivity of these catalysts were investigated as a function of the Ti content and it was found that the hydrogenolysis reaction (C2H6 formation) was predominant in regions of low Ti content, while the hydrogenation reaction (C3H6 formation) proceeded in regions of high Ti content. The in situ photoluminescence, diffuse reflectance absorption, FT-IR, XAFS (XANES and EXAFS), and XPS spectroscopic investigations of these Ti/Si binary oxides indicated that the titanium oxide species are highly dispersed in the SiO2 matrices and exist in a tetrahedral coordination exhibiting a characteristic photoluminescence spectrum. The charge transfer excited state of the tetrahedrally coordinated titanium oxide species plays a significant role in the efficient photoreaction with a high selectivity for the hydrogenolysis of CH3CCH to produces mainly C2H6 and CH4, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity for the hydrogenation of CH3CCH to produce C3H6, being similar to reactions of the powdered TiO2 catalysts. The good parallel relationship between the yield of the photoluminescence and the specific photocatalytic reactivity of the Ti/Si binary oxides as a function of the Ti content clearly indicates that the high photocatalytic reactivity of the Ti/Si binary oxides having low Ti content is associated with the high reactivity of the charge transfer excited state of the isolated titanium oxide species in tetrahedral coordination, [Ti3+-O−]*. [ABSTRACT FROM AUTHOR]