Juan J. Delgado

CuOx−TiO2 Photocatalysts for H2 Production from Ethanol and Glycerol Solutions†

Hydrogen production by photocatalytic reforming of aqueous solutions of ethanol and glycerol was studied with the use of impregnated and embedded CuO(x)/TiO(2) photocatalysts. Embedded CuO(x)@TiO(2) was prepared by a water-in-oil microemulsion method, which consists in the formation of Cu nanoparticles in the microemulsion followed by controlled hydrolysis and condensation of tetraisopropyl orthotitanate with the aim of covering the protected metal particles with a surrounding layer of porous titanium oxyhydroxide. Mild calcination leads to the complete removal of the organic residues, the crystallization of TiO(2), and an unavoidable oxidation of copper. Two reference samples were prepared by classical wet impregnation of preformed TiO(2) with different ratios of anatase, rutile, and brookite polymorphs. The two supports were prepared by sol-gel (TiO(2)-SG) and microemulsion (TiO(2)-ME) methods. Superior performances have been observed for the embedded system, which shows higher hydrogen production rates with respect to the impregnated systems using either ethanol or glycerol as sacrificial molecules. Deep structural characterization of the materials has been performed by coupling high resolution transmission electron microscopy (HRTEM), high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure (XAFS), and electron paramagnetic resonance (EPR) techniques. Correlation between copper oxidation state and its dispersion and reactivity has been attempted. Finally, the stability of the CuO(x)/TiO(2) catalysts was also studied with respect to carbonaceous deposits and copper leaching.

A Noble-Metal-Free Catalyst Derived from Ni-Al Hydrotalcite for Hydrogen Generation from N2H4⋅H2O Decomposition†

Storing hydrogen safely and efficiently is one of the major technological barriers preventing the widespread application of hydrogen-fueled cells, such as proton exchange membrane fuel cells (PEMFCs). Hydrous hydrazine (N2H4·H2O) is considered as a promising liquid hydrogen storage material owing to the high content of hydrogen (7.9%) and the advantage of CO-free H2 produced. [1] In particular, hydrous hydrazine offers great potential as a hydrogen storage material for some special applications, such as unmanned space vehicles and submarine power sources, where hydrazine is usually used as a propellant. The decomposition of hydrazine proceeds by two typical reaction routes:

Nanostructured Cu/TiO2 Photocatalysts for H2 Production from Ethanol and Glycerol Aqueous Solutions.

The sustainable development of the human society requires an increasing use of renewable raw materials and energy sources. In this context, photocatalysis represents a promising and necessary way to produce solar fuels and chemicals. The photocatalytic hydrogen production of renewable oxygenated compounds from aqueous solutions could represent an important alternative 6] to the more complex water splitting, or to conventional thermal reforming processes. Noble and base metals, including Pt, Au, Pd, Ni, Cu, and Ag, have been reported to be very efficient at increasing the production of H2 in TiO2 photocatalysis. [11] Increasing attention has been devoted to Cu2O and CuO as photocatalysts. [12, 13] Both copper oxides are abundant natural p-type semiconductors and are attractive owing to their virtual non-toxicity. Their bandgaps (2.1 eV for Cu2O and 1.2 eV for CuO) are suitable for photosplitting water to produce hydrogen by using visible light. However, these materials have been shown to be unstable in electrolytic solutions owing to their facile photooxidation. Siripala et al. prepared a Cu2O/TiO2 heterojunction by electrodeposition of copper oxide; the device was shown to perform photoelectrolysis of water, the TiO2 layer providing protection against photocorrosion. Herein, a cheap and active photocatalysts based on Cu nanoparticles dispersed on TiO2 supports, which are capable of operating under solar radiation, are investigated for the production of hydrogen from ethanol and glycerol. Second generation ethanol and sugars, extracted from lignocellulosic parts of vegetables, and glycerol, produced as a by-product of bio-diesel, are attractive and largely available sacrificial agents. 16] Two different TiO2 supports were prepared, the former from titanium isopropoxide (TiO2-SG) [17] by a sol–gel method, the latter from titanyl sulphate (TiO2-PS) by precipitation, [18] followed in both cases by calcination at 450 8C for 6 h. TiO2-SG (surface area 69 mg ) was composed of a mixture of polymorphs (Figure S1 in the Supporting Information). The analysis of its XRD pattern, following the work of Zhang et al. , evidenced the presence of anatase (64 wt %), rutile (8 wt %) and brookite (28 wt %). Mean crystallite sizes of 11, 32, and 11 nm were calculated for anatase, rutile, and brookite, respectively. TiO2-PS possessed a slightly higher surface area (104 m 2 g ). Its powder XRD pattern showed the presence of a pure anatase phase (Figure S1 in the Supporting Information), with a mean crystallite size of 8 nm. The photodeposition of Cu on the surface of both TiO2 supports was performed by using UV/Vis irradiation (2 h) in the presence of copper nitrate and CH3OH as a hole scavenger (Figure S2). XRD analysis of the Cu/TiO2 nanocomposites did not allow the identification of Cu-related phases probably because of their low amount and/or high dispersion. Therefore, the Cu phases photodeposited on TiO2 supports were characterized by using X-ray absorption near-edge structure (XANES) or extended X-ray absorption fine structure (EXAFS) spectroscopy. Immediately after photodeposition, XANES spectra at the Cu K edge was in good agreement with that of Cu foil used as reference standard (Figure 1), thus indicating that copper is deposited in the form of zero-valent copper. The results of the analysis of the EXAFS spectra are summarized in Table 1.

Bifunctional Hybrid SiO2 Nanoparticles Showing Synergy between Core Spin Crossover and Shell Luminescence Properties

It is well-known that certain octahedral coordination compounds with electronic configurations from d to d can undergo spin crossover (SCO) between high-spin (HS) and low-spin (LS) states. The spin state, and consequently the color, size, and magnetic properties of these SCO systems can be tuned through external stimuli such as temperature, pressure, light, magnetic fields, and guest absorption/desorption. Additionally, some SCO compounds exhibit abrupt transitions with large hysteresis loops, which confer a memory effect to these materials. Therefore, SCO systems offer some promising opportunities for application in information processing, data storage, molecular switches, and/or display devices. For integration into functional devices, SCO materials need to be prepared at the nanometer scale, whilst retaining their magnetic and cooperative behavior. As a result, different research groups have focused their studies on the synthesis and physicochemical characterization of spin-crossover nanoparticles (SCONPs). They have demonstrated that the SCO phenomenon is preserved at the nanometer scale and that it is possible to tune the transition temperatures and the size of the hysteresis loop by controlling the particle size. Parallel to this approach, some other research groups have concentrated their studies on the design of new molecular systems that combine spin crossover and other interesting properties such as luminescence. To the best of our knowledge, only one attempt has been made to prepare bifunctional SCO/luminescence nanoparticles. Specifically, Bousseksou and co-workers have obtained nanoparticles of the SCO complex [Fe(NH2Trz)3](tos)2 (NH2Trz = 4-amino-1,2,4-triazole; tos = tosyl) doped with the fluorescent agent Rhodamine 110. In this system, the emission spectrum of the Rhodamine at room temperature overlaps with the A1g!T1g absorption band of the iron(ii) polymer in the LS state and the emission is partially quenched. When the temperature is raised to 320 K (HS regime), the A1g!T1g absorption band bleaches and the emission intensity increases. Herein, we propose an alternative strategy to prepare bifunctional SCO/luminescence nanoparticles which consists of using silica as a matrix for the SCO component (Figure 1). Although silica nanoparticles (SiO2NPs) have been widely used as supports for the fabrication of multifunctional materials that have a vast number of important potential applications in fields such as drug delivery, biosensors, cell labeling, and so forth, as far as we know, no examples of hybrid SiO2NPs SCO systems have been reported so far. Silica is a particularly suitable material for the preparation of SiO2NPs SCO systems because its high porosity allows for the incorporation of SCO compounds and as silica does not absorb light and does not interfere with magnetic fields the SCO compounds inside the SiO2NPs will keep their original optical and magnetic properties. Additionally, the surfaces of these SiO2NPs SCO systems can be functionalized by grafting active species, such as fluorophores, to afford bifunctional SCO/luminescence nanomaterials. The first results of this original approach are reported, herein. As the SCO material we have used a 1D Fe complex {[Fe(HTrz)2(Trz)](BF4)}n (hereafter Fe-Trz; HTrz = 1,2,4-1H-

3 D Characterization of Gold Nanoparticles Supported on Heavy Metal Oxide Catalysts by HAADF‐STEM Electron Tomography

Living on the edge: Three-dimensional reconstructions from electron tomography data recorded from Au/Ce(0.50)Tb(0.12)Zr(0.38)O(2-x) catalysts show that gold nanoparticles (see picture; yellow) are preferentially located on stepped facets and nanocrystal boundaries. An epitaxial relationship between the metal and support plays a key role in the structural stabilization of the gold nanoparticles.

Magnetic Nanoparticles-Templated Assembly of Protein Subunits: A New Platform for Carbohydrate-Based MRI Nanoprobes

A new approach for the preparation of carbohydrate-coated magnetic nanoparticles is reported. In a first step, we show that the pH-driven assembly-disassembly natural process that occurs in apoferritin protein is effective for the encapsulation of maghemite nanoparticles of different sizes: 4 and 6 nm. In a second step, we demonstrate that the presence of functional amine groups in the outer shell of apoferritin allows functionalization with two carbohydrates, N-acetyl-D-glucosamine and d-mannose. High-resolution electron microscopy (HREM), high angle annular dark field scanning electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), and SQUID technique have been used to characterize the magnetic samples, termed herein Apomaghemites. The in vivo magnetic resonance imaging (MRI) studies showed the efficiency in contrasting images for these samples; that is, the r(2) NMR relaxivities are comparable with Endorem (a commercial superparamagnetic MRI contrast agent). The r(2) relaxivity values as well as the pre-contrast and post-contrast T(2)*-weighted images suggested that our systems could be used as perspective superparamagnetic contrast agents for magnetic resonance imaging (MRI). The carbohydrate-functionalized Apomaghemite nanoparticles retained their recognition abilities, as demonstrated by the strong affinity with their corresponding carbohydrate-binding lectins.

Highly Ordered Mesoporous Carbon as Catalyst for Oxidative Dehydrogenation of Ethylbenzene to Styrene

We demonstrate that mesoporous carbon without deposition of metal particles is a highly active catalyst. It exhibits both high activity and selectivity in oxidative dehydrogenation of ethylbenzene to styrene, as well as long catalytic stability when compared with activated carbon. Both the as-prepared mesoporous carbon and the active coke formed during the initial stage of the reaction play an important role in the catalytic performance. XPS and IR techniques reveal that the surface oxygen functional groups formed during the reaction are the active sites for the reaction. The ordered mesoporous structure is beneficial for mass transport in catalytic reaction exhibiting long term stability in contrast to activated carbon.

Optimization of tin dioxide nanosticks faceting for the improvement of palladium nanocluster epitaxy

Semispherical palladium nanoclusters have been epitaxed on {110} facets of tin dioxide nanosticks. The synthesis of tin dioxide nanoparticles has been optimized to obtain a crystallite shape with a maximum surface area lying on the rutile structure {110} planes, which are the most active for gas sensing. For this purpose, we describe a microwave method, which allowed us to obtain monocrystalline stick-like tin dioxide nanoparticles (so-called nanosticks) with rectangular prism shape. These nanosticks present long lateral {110} faces, squared cross-section 5–25 nm wide, and lengths of up to 0.5 μm.

Influence of the Preparation Procedure on the Catalytic Activity of Gold Supported on Diamond Nanoparticles for Phenol Peroxidation

The catalytic activity of diamond-supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol (50 g L(-1)) and H(2)O(2) excesses (100 g L(-1)) and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of O(2) evolved two different reactions of H(2)O(2) decomposition (the Fenton reaction at acidic pH values and spurious O(2) evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and 35 kJ mol(-1)). By using dimethylsulfoxide as a radical scavenger and N-tert-butyl-α-phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected PBN-OCH(3) adduct was detected, supporting the generation of HO(.), characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as H(2)O(2) decomposition at pH 4 (due to the barrierless attack of HO(.) to phenol), but increases the activation energy gradually up to about 90 kJ mol(-1) at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 (49 kJ mol(-1)).

Fully Reversible Metal Deactivation Effects in Gold/Ceria–Zirconia Catalysts: Role of the Redox State of the Support

Gold nanoparticles supported on reducible oxides are highly interesting catalytic materials. In particular, they are known to exhibit exceptional activity for CO oxidation, lowtemperature water–gas shift (LT-WGS), and selective oxidation of CO in the presence of a large excess of hydrogen (PROX). 20–24] Despite the extraordinary research effort devoted to these catalysts, there are still some key questions about the nanostructural constitution and chemical properties of the gold sites involved in the above reactions that require further clarification. The relationship between the redox state of the support and the chemical properties of gold nanoparticles is one of these major open questions. 5] Its understanding, however, is critically important to fully interpret catalysis by Au/reducible oxide systems, particularly in the case of processes like LTWGS, 19] PROX, and hydrogenation reactions, which typically occur under net reducing conditions. To gain further information on this issue, we investigated CO adsorption on an Au/Ce0.62Zr0.38O2 (Au/CZ) sample subjected to different redox pretreatments. In our experimental approach, FTIR spectroscopic and volumetric adsorption techniques were combined with studies on ultimate oxygen storage capacity (OSC), metal dispersion, as determined by high-resolution TEM (HRTEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and X-ray photoelectron spectroscopy (XPS). By this approach, the influence of the redox state of the support on the CO adsorption capability of Au nanoparticles could be established on a quantitative basis. In contrast with earlier proposals suggesting that gold catalysts do not exhibit a strong metal/support interaction (SMSI) effect, the results presented and discussed herein indicate that the behavior of our Au/CZ shows close resemblances with those of a number of noble metal/reducible oxide systems which are acknowledged to show this effect. Our experimental approach also allowed us to show that the absorption coefficient of the n[CO(Au)] band depends on the redox state of the support. The implications of this finding for the use of integrated absorption data as a quantitative tool for characterizing the changes of CO adsorption capability occurring in gold nanoparticles supported on reducible oxides is discussed. Figure 1 shows the n(CO) FTIR spectra recorded on the same sample disk successively submitted to a) oxidizing treatment at 523 K (Au/CZ-O523); b) pretreatment (a) followed by reduction at 473 K (Au/CZ-O523-R473); and