Stability and Reversible Oxidation of Sub-Nanometric Cu5 Metal Clusters: Integrated Experimental Study and Theoretical Modeling

Sub-nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude "breathing" motions. A chemical phase diagram for Cu oxidation states of the Cu5 -oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu.

Electrochemical Fine-Tuning of the Chemoresponsiveness of Langmuir-Blodgett Graphene Oxide Films

Graphene oxide has been widely deployed in electrical sensors for monitoring physical, chemical, and biological processes. The presence of abundant oxygen functional groups makes it an ideal substrate for integrating biological functional units to assemblies. However, the introduction of this type of defects on the surface of graphene has a deleterious effect on its electrical properties. Therefore, adjusting the surface chemistry of graphene oxide is of utmost relevance for addressing the immobilization of biomolecules, while preserving its electrochemical integrity. Herein, we describe the direct immobilization of glucose oxidase onto graphene oxide-based electrodes prepared by Langmuir-Blodgett assembly. Electrochemical reduction of graphene oxide allowed to control its surface chemistry and, by this, regulate the nature and density of binding sites for the enzyme and the overall responsiveness of the Langmuir-Blodgett biofilm. X-ray photoelectron spectroscopy, surface plasmon resonance, and electrochemical measurements were used to characterize the compositional and functional features of these biointerfaces. Covalent binding between amine groups on glucose oxidase and epoxy and carbonyl groups on the surface of graphene oxide was successfully used to build up stable and active enzymatic assemblies. This approach constitutes a simple, quick, and efficient route to locally address functional proteins at interfaces without the need for additives or complex modifiers to direct the adsorption process.

Synthesis of photocatalytic cysteine-capped Cu≈10 clusters using Cu5 clusters as catalysts

We report an easily scalable synthesis method for the preparation of cysteine-capped Cu_≈10 clusters through the reduction of Cu(II) ions with NaBH₄, using Cu₅ clusters as catalysts. The presence of such catalytic clusters allows controlling the formation of the larger Cu_≈10 clusters and prevents the production of copper oxides or Cu(I)-cysteine complexes, which are formed when Cu₅ is absent or at lower concentrations, respectively. These results indicate that small catalytic clusters could be involved, as precursor species before the reduction step, in the different methods developed for the synthesis of clusters. The visible light-absorbing Cu_≈10 clusters, obtained by the cluster-catalysed method, display high photocatalytic activities for the decomposition of methyl orange with visible light.

Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments

Co- and Ni-based layered hydroxides constitute a unique class of two-dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α-NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co-O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so-called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational-experimental investigation of the electronic and structural details of α-NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.

Synthesis and characterization of Ag2S and Ag2S/Ag2(S,Se) NIR nanocrystals

Syntheses of metal sulfide nanocrystals (NCs) by heat-up routes in the presence of thiols yield NC arrangements difficult to further functionalize and transfer to aqueous media. By means of different NMR techniques, and exemplified by Ag2S NCs, a metal-organic polymer formed during the synthesis acting as a ligand has been identified to be responsible for such aggregation. In this work, a new synthetic hot-injection strategy is presented to synthesize Ag2S NCs which are easily ligand exchangeable in water. Furthermore, the hot-injection route allows an extra NC treatment with Se to produce Ag2S/Ag2(S,Se) NCs with improved optical properties with respect to the Ag2S cores, and better resistance to oxidation, as demonstrated by X-ray absorption experiments.

Increasing the optical response of TiO2 and extending it into the visible region through surface activation with highly stable Cu5 clusters

The decoration of semiconductors with subnanometer-sized clusters of metal atoms can have a strong impact on the optical properties of the support. The changes induced differ greatly from effects known for their well-studied, metallic counterparts in the nanometer range. In this work, we study the deposition of Cu5 clusters on a TiO2 surface and investigate their influence on the photon-absorption properties of TiO2 nanoparticles via the computational modeling of a decorated rutile TiO2 (110) surface. Our findings are further supported by selected experiments using diffuse reflectance and X-ray absorption spectroscopy. The Cu5 cluster donates an electron to TiO2, leading to the formation of a small polaron Ti3+ 3d1 state and depopulation of Cu(3d) orbitals, successfully explaining the absorption spectroscopy measurements at the K-edge of copper. A monolayer of highly stable and well fixated Cu5 clusters is formed, which not only enhances the overall absorption, but also extends the absorption profile into the visible region of the solar spectrum via direct photo-induced electron transfer and formation of a charge-separated state.

Iron-based nanoparticles prepared from yerba mate extract. Synthesis, characterization and use on chromium removal

Iron-based nanoparticles were synthesized by a rapid method at room temperature using yerba mate (YM) extracts with FeCl₃ in different proportions. Materials prepared from green tea (GT) extracts were also synthesized for comparison. These materials were thoroughly characterized by chemical analyses, XRD, magnetization, SEM-EDS, TEM-SAED, FTIR, UV-Vis, Raman, Mössbauer and XANES spectroscopies, and BET area analysis. It was concluded that the products are nonmagnetic iron complexes of the components of the extracts. The applicability of the materials for Cr(VI) (300 μM) removal from aqueous solutions at pH 3 using two Cr(VI):Fe molar ratios (MR), 1:3 and 1:0.5, has been tested. At Cr(VI):Fe MR = 1:3, the best YM materials gave complete Cr(VI) removal after two minutes of contact, similar to that obtained with commercial nanoscale zerovalent iron (N25), with dissolved Fe(II), and with a likewise prepared GT material. At a lower Cr(VI):Fe MR (1:0.5), although Cr(VI) removal was not complete after 20 min of reaction, the YM nanoparticles were more efficient than N25, GT nanoparticles and Fe(II) in solution. The results suggest that an optimal Cr(VI):Fe MR ratio could be reached when using the new YM nanoparticles, able to achieve a complete Cr(VI) reduction, and leaving very low Cr and Fe concentrations in the treated solutions. The rapid preparation of the nanoparticles would allow their use in removal of pollutants in soils and groundwater by direct injection of the mixture of precursors.

Unexpected Optical Blue Shift in Large Colloidal Quantum Dots by Anionic Migration and Exchange

Compositional changes taking place during the synthesis of alloyed CdSeZnS nanocrystals (NCs) allow shifting of the optical features to higher energy as the NCs grow. Under certain synthetic conditions, the effect of those changes on the surface/interface chemistry competes with and dominates over the conventional quantum confinement effect in growing NCs. These changes, identified by means of complementary advanced spectroscopic techniques such as XPS (X-ray photoelectron spectroscopy) and XAS (X-ray absorption spectroscopy), are understood in the frame of an ion migration and exchange mechanism taking place during the synthesis. Control over the synthetic routes during NC growth represents an alternative tool to tune the optical properties of colloidal quantum dots, broadening the versatility of the wet chemical methods.

Unexpected compositional and structural modification of CoPt3 nanoparticles by extensive surface purification

We combined synchrotron small angle X-ray scattering, X-ray fluorescence and extended X-ray absorption fine structure spectroscopy to probe the structure of chemically synthesized CoPt3 nanoparticles (NPs) after ligand removal via the commonly accepted solvent/nonsolvent approach. We showed that the improved catalytic activity of extensively purified NPs could not be explained only in terms of a "cleaner" surface. We found that extensive surface purification results in the substantial leaching of the Co atoms from the chemically synthesized CoPt3 NPs transforming them into CoPt3/Pt core/shell structures with an unexpectedly thick (∼0.5 nm) Pt shell. We indicated that the improved catalytic activity of extensively purified NPs in octyne hydrogenation reaction can be explained by the formation of CoPt3/Pt core/shell structures. Also, we demonstrated that drastic compositional and structural transformation of water transferred CoPt3 NPs was rather a result of extensive removal of native ligands via a solvent/nonsolvent approach than leaching of cobalt atoms in aqueous media. We expect that these findings can be relevant to other transition metal based multicomponent NPs.

Synthesis of nickel entities: From highly stable zerovalent nanoclusters to nanowires. Growth control and catalytic behavior

Non-noble metal nanoclusters synthesis is receiving increased attention due to their unique catalytic properties and lower cost. Herein, the synthesis of ligand-free Ni nanoclusters with an average diameter of 0.7 nm corresponding to a structure of 13 atoms is presented; they exhibit a zero-valence state and a high stability toward oxidation and thermal treatment. The nanoclusters formation method consists in the electroreduction of nickel ions inside an ordered mesoporous alumina; also, by increasing the current density, other structures can be obtained reaching to nanowires of 10 nm diameter. A seed-mediated mechanism is proposed to explain the growth to nanowires inside these mesoporous cavities. The size dependence on the catalytic behavior of these entities is illustrated by studying the reduction of methylene blue where the nanoclusters show an outstanding performance.

Understanding and Reducing Photothermal Forces for the Fabrication of Au Nanoparticle Dimers by Optical Printing

Optical printing holds great potential to enable the use of the vast variety of colloidal nanoparticles (NPs) in nano- and microdevices and circuits. By means of optical forces, it enables the direct assembly of NPs, one by one, onto specific positions of solid surfaces with great flexibility of pattern design and no need of previous surface patterning. However, for unclear causes it was not possible to print identical NPs closer to each other than 300 nm. Here, we show that the repulsion restricting the optical printing of close by NPs arises from light absorption by the printed NPs and subsequent local heating. By optimizing heat dissipation, it is possible to reduce the minimum separation between NPs. Using a reduced graphene oxide layer on a sapphire substrate, we demonstrate for the first time the optical printing of Au-Au NP dimers. Modeling the experiments considering optical, thermophoretic, and thermo-osmotic forces we obtain a detailed understanding and a clear pathway for the optical printing fabrication of complex nano structures and circuits based on connected colloidal NPs.

Inorganically coated colloidal quantum dots in polar solvents using a microemulsion-assisted method

The dielectric nature of organic ligands capping semiconductor colloidal nanocrystals (NCs) makes them incompatible with optoelectronic applications. For this reason, these ligands are regularly substituted through ligand-exchange processes by shorter (even atomic) or inorganic ones. In this work, an alternative path is proposed to obtain inorganically coated NCs. Differently to regular ligand exchange processes, the method reported here produces core-shell NCs and the removal of the original organic shell in a single step. This procedure leads to the formation of connected NCs resembling 1D worm-like networks with improved optical properties and polar solubility, in comparison with the initial CdSe NCs. The nature of the inorganic shell has been elucidated by X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Photoelectron Spectroscopy (XPS). The 1D morphology along with the lack of long insulating organic ligands and the higher solubility in polar media turns these structures very attractive for their further integration into optoelectronic devices.

Oxidation Induced Doping of Nanoparticles Revealed by in Situ X-ray Absorption Studies

Doping is a well-known approach to modulate the electronic and optical properties of nanoparticles (NPs). However, doping at nanoscale is still very challenging, and the reasons for that are not well understood. We studied the formation and doping process of iron and iron oxide NPs in real time by in situ synchrotron X-ray absorption spectroscopy. Our study revealed that the mass flow of the iron triggered by oxidation is responsible for the internalization of the dopant (molybdenum) adsorbed at the surface of the host iron NPs. The oxidation induced doping allows controlling the doping levels by varying the amount of dopant precursor. Our in situ studies also revealed that the dopant precursor substantially changes the reaction kinetics of formation of iron and iron oxide NPs. Thus, in the presence of dopant precursor we observed significantly faster decomposition rate of iron precursors and substantially higher stability of iron NPs against oxidation. The same doping mechanism and higher stability of host metal NPs against oxidation was observed for cobalt-based systems. Since the internalization of the adsorbed dopant at the surface of the host NPs is driven by the mass transport of the host, this mechanism can be potentially applied to introduce dopants into different oxidized forms of metal and metal alloy NPs providing the extra degree of compositional control in material design.

Understanding the Zr and Si interdispersion in Zr1−xSixO2 mesoporous thin films by using FTIR and XANES spectroscopy

Zr_1−xSi_xO₂ mesoporous oxide thin films were obtained and their interdispersion was demonstrated by careful characterization using spectroscopic techniques.

Photostability of gold nanoparticles with different shapes: the role of Ag clusters

Anisotropic gold nanostructures prepared by the seed method in the presence of Ag ions have been used to study their photostability to low-power UV irradiation (254 nm) at room temperature. It has been observed that, whereas spheres are very stable to photoirradiation, rods and prisms suffer from photocorrosion and finally dissolve completely with the production of Au(III) ions. Interpretation of these differences is based on the presence of semiconductor-like Ag clusters, adsorbed onto rods and prisms, able to photocorrode the Au nanoparticles, which are absent in the case of Au spheres. We further show direct evidence of the presence of Ag clusters in Au nanorods by XANES. These results confirm a previous hypothesis (J. Am. Chem. Soc., 2014, 136, 1182-1185) about the major influence of very stable small Ag clusters, not only on the anisotropic formation of nanostructures but also on their photostability.

Controlled growth of extended arrays of CoSi2 hexagonal nanoplatelets buried in Si(001), Si(011) and Si(111) wafers

Because of their high electrical conductivity CoSi2 nanostructures are potential candidates for preparing ordered nano-arrays to be used as electrode interconnectors and contacts in microelectronic devices. We here describe a controlled procedure for the endotaxial growth of hexagonal CoSi2 nanoplatelets buried in differently oriented single crystalline Si wafers on which a Co-doped SiO2 thin film was previously deposited. These nanomaterials were obtained by a clean procedure consisting of isothermal annealing at 750 °C under a He atmosphere of Co-doped SiO2 thin films deposited onto the surface of three differently oriented flat Si substrates, namely Si(001), Si(011) and Si(111). Buried CoSi2 nanoplatelets are in all cases spontaneously formed as a consequence of the diffusion of Co atoms into the silicon wafer and their reaction with host Si atoms. Our TEM and GISAXS analyses demonstrated that these arrays, irrespective of host Si orientation, consist of CoSi2 hexagonal nanoplatelets in all cases parallel to Si{111} crystallographic planes. Additionally, the dimensions of the nanoplatelets were consistently determined by TEM and GISAXS for the three different host Si single crystal orientations.

Aminopropyl-modified mesoporous silica SBA-15 as recovery agents of Cu(II)-sulfate solutions: Adsorption efficiency, functional stability and reusability aspects

Hybrid mesoporous materials are potentially useful for metal ion scavenging and retrieval because of their high surface areas, controlled accessibility and tailored functionalization. Some aspects that are linked to the performance of HMM include pore accessibility, stability of the organic functions and reusability. Knowledge of these aspects is critical in the design of adsorption-desorption protocols. In this work we produce and characterize propylamino-substituted large pore silica (SBA-15-N), which is submitted to Cu(II) adsorption from copper sulfate solutions, followed by desorption in acid media and material regeneration. We find that the hybrid material is an efficient adsorbent (1.15-1.75mmol Cu(II)g(-1)), although a fraction of the organic groups is lost during the adsorption process. An X-ray photoelectron spectroscopy (XPS) study demonstrates that the contents of amino groups are higher in the material surface, leading to different behaviors in Cu(II) complexation along the material. These materials can be regenerated by exposure to acidic media. Thermal processing of the hybrid materials leads to better durability in aqueous solutions during reprocessing, due to enhanced polycondensation of the inorganic framework. Thermally treated samples, once regenerated, are efficient adsorbents in a second step of Cu(II) adsorption. We discuss the materials processing factors involved in the improved adsorption of Cu(II), its quantitative release and reusability of the material.

TiO₂-photocatalytic reduction of pentavalent and trivalent arsenic: production of elemental arsenic and arsine

Heterogeneous photocatalytic reduction of As(V) and As(III) at different concentrations over TiO(2) under UV light in deoxygenated aqueous suspensions is described. For the first time, As(0) was unambiguously identified together with arsine (AsH(3)) as reaction products. As(V) reduction requires the presence of an electron donor (methanol in the present case) and takes place through the hydroxymethyl radical formed from methanol oxidation by holes or hydroxyl radicals. On the contrary, As(III) reduction takes place through direct reduction by the TiO(2)-conduction band electrons. Detailed mechanisms for the photocatalytic processes are proposed. Although reduction to solid As(0) is convenient for purposes of As removal from water as a deposit on TiO(2), attention must be paid to formation of AsH(3), one of the most toxic forms of As, and strategies for AsH(3) treatment should be considered.

Shape changes of Pt nanoparticles induced by deposition on mesoporous silica

Polyvinylpyrollidone (PVP)-capped platinum nanoparticles (NPs) are found to change shape from spherical to flat when deposited on mesoporous silica substrates (SBA-15). Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) analyses are used in these studies. The SAXS results indicate that, after deposition, the 2 nm NPs have an average gyration radius 22% larger than in solution, while the EXAFS measurements indicate a decrease in first neighbor co-ordination number from 9.3 to 7.4. The deformation of these small capped NPs is attributed to interactions with the surface of the SBA-15 support, as evidenced by X-ray absorption near-edge structure (XANES).

"Naked" gold nanoparticles supported on HOPG: melanin functionalization and catalytic activity

Reductive electrodesorption has been used to produce "naked" gold nanoparticles (AuNPs) 3 nm in size on HOPG from different thiolate-capped AuNPs. The clean AuNPs transform the electrocatalytic inert HOPG into an active surface for hydrogen peroxide electroreduction, causing a lowering of the cathodic overpotential of 0.25 V with respect to the Au(111) surface. Compared to the plain gold substrates, the nanostructures promote only a slight increase in the hydrogen evolution reaction. In a second modification step a ∼1 nm thick melanin-iron coating is electrochemically formed around the AuNPs. This ultrathin melanin-iron coating largely improves the catalytic activity of the bare AuNPs for both hydrogen peroxide electroreduction and hydrogen evolution reaction. This strategy, which integrates electrochemistry and nanotechnology, can be applied to the preparation of efficient "naked" AuNPs and organic-iron capped AuNPs catalysts.

Synthesis and characterization of gold at gold(i)-thiomalate core at shell nanoparticles

In this paper, the synthesis of gold at gold(I)-thiolate core at shell nanoparticles is described for the first time. The chemical nature and structure of these nanoparticles were characterized by a multi-technique approach. The prepared particles consist of gold metallic cores, about 1 nm in size, surrounded by stable gold(I)-thiomalate shells (Au at Au(I)-TM). These nanoparticles could be useful in medicine due to the interesting properties that gold(I)-thiomalate has against rheumatoid arthritis. Furthermore, the described results give new insights in the synthesis and characterization of metallic and core at shell nanoparticles.

Electronic Perturbation in a Molecular Nanowire of [IrCl5(NO)]− Units

The nitrosyl in [IrCl5(NO)]- is probably the most electrophilic known to date. This fact is reflected by its extremely high IR frequency in the solid state, electrochemical behavior, and remarkable reactivity in solution. PPh4[IrCl5(NO)] forms a crystal in which the [IrCl5(NO)]- anions are in a curious wire-like linear arrangement, in which the distance between the N--O moiety of one anion and the trans chloride of the upper one nearby is only 2.8 A. For the same complex [IrCl5(NO)]- but with a different counterion, Na[IrCl5(NO)], the anions are stacked one over the other in a side-by-side arrangement. In this case the electronic distribution can be depicted as the closed-shell electronic structure Ir III-NO+, as expected for any d(6) third-row transition metal complex. However, in PPh4[IrCl5(NO)] an unprecedented electronic perturbation takes place, probably due to NO*-Cl- acceptor-donor interactions among a large number of [IrCl5(NO)]- units, favoring a different electronic distribution, namely the open-shell electronic structure Ir IV-NO*. This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidation state for iridium in PPh4[IrCl5(NO)] is +4, as compared with +3 in K[IrCl5(NO)]. In agreement, solid-state DFT calculations show that the ground state for [IrCl5(NO)]- in the PPh4+ salt comprises an open-shell singlet with an electronic structure which encompasses half of the spin density mainly localized on a metal-centered orbital, and the other half on an NO-based orbital. The electronic perturbation could be seen as an electron promotion from a metal-chloride to a metal-NO orbital, due to the small HOMO-LUMO gap in PPh4[IrCl5(NO)]. This is probably induced by electrostatic interactions acting as a result of the closeness and wire-like spatial arrangement of the Ir metal centers, imposed by lattice forces due to pi-pi stacking interactions among the phenyl rings in PPh4+. Experimental and theoretical data indicate that in PPh4[IrCl5(NO)] the Ir-N-O moiety is partially bent and tilted.

Influence of N-Doping on the Structure and Electronic Properties of Titania Nanoparticle Photocatalysts

N-containing TiO(2)-based nanostructured materials (average particle size approximately 10 nm) with an anatase-type structure were investigated using oxygen (O) K-edge and titanium (Ti) K- and L-edge X-ray absorption near-edge spectroscopy (XANES). The Ti K pre-edge features indicate that samples predominantly contain ([6])Ti with some ([5])Ti, and there is no evidence for ([4])Ti. We observed that those samples with a larger fraction of Ti in a fivefold coordination, that is, with a significant number of oxygen vacancies, also present a modified Ti environment at the medium-range scale. The presence of these defects drastically modifies the electronic structure of the conduction band, as evidenced by the O K XANES spectra, but does not result in the presence of reduced Ti(3+) states. We discuss the influence of N-doping on titania nanoparticles and their structure, electronics and photocatalytic activity.

Temperature Effect on the Synthesis of Au−Pt Bimetallic Nanoparticles

Pt-Au bimetallic nanoparticles have been synthesized by the polyol method and stabilized with poly(vinylpyrrolidone) (PVP), modifying the temperature of synthesis. Interesting structure changes were observed in the nanoparticles as the temperature was varied. At lower temperatures no bimetallic nanoparticles were detected, but as the temperature increased bimetallic nanoparticles started to appear, commonly obtaining core-shell nanoparticles, always covered by the polymer. This originates the modification of the optical response of the system in the UV-visible region. An absorption peak centered at 520 nm at low temperatures was observed (100-110 degrees C); at higher temperatures (130-170 degrees C) there were non detectable absorption peaks, and finally at the two highest temperatures (180-190 degrees C) the reappearance of an absorption feature centered at 510 nm was noticed. These UV-visible results indirectly imply the composition of the surface of the particle. The structure of the particles has been determined using transmission electron microscopy and high-angle annular dark field (HAADF), the latter being a powerful technique to determine the structural composition of the particles and allowing a direct correlation of the optical response with their structural composition. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were also performed on the samples and their results support the idea of a Pt(core)-Au(shell) structure with the elements segregated from each other. The combination of these experimental techniques with calculated UV-vis absorption spectra allowed, in a reliable way, the elucidation of the nanoparticles structure and elemental distribution.

Structure of extremely nanosized and confined In-O species in ordered porous materials

Perturbed-angular correlation, x-ray absorption, and small-angle x-ray scattering spectroscopies were suitably combined to elucidate the local structure of highly diluted and dispersed InOx species confined in the porous of the ZSM5 zeolite. This novel approach allow us to determined the structure of extremely nanosized In-O species exchanged inside the 10-atom-ring channel of the zeolite, and to quantify the amount of In2O3 crystallites deposited onto the external zeolite surface.

In situ and ex situ XANES study of nanodispersed Mo species in zeolites used in fine chemistry catalysis

Mo K-edge XANES experiments on Mo-containing zeolites at low Mo loading (1 and 2 wt% of Mo on H-ZSM-11, H-BETA and H-ZSM-5 catalysts), active in fine chemistry reactions, were performed ex situ as function of sample calcination temperature in air (in the range 773-973 K) or in situ at 873 and 973K under N2 flow. The results showed a 4-fold oxygen coordination for the incorporated Mo species in the activated (dehydrated) state. Combining these results with additional data evidences an almost total Mo exchange inside the zeolite channels.