Structure sensitivity reaction of chloroform hydrodechlorination to light olefins using Pd catalysts supported on carbon nanotubes and carbon nanofibers.

The upgrading of wasted chloroform in hydrodechlorination for the production of olefins such as ethylene and propylene is studied by employing four catalysts (PdCl/CNT, PdCl/CNF, PdN/CNT, and PdN/CNF) prepared by different precursors (PdCl2 and Pd(NO3)2) supported on carbon nanotubes (CNT) or carbon nanofibers (CNF). TEM and EXAFS-XANES results confirm that Pd nanoparticle size increases in the order: PdCl/CNT < PdCl/CNF âˆ¼ PdN/CNT < PdN/CNF, descending the electron density of Pd nanoparticles in the same order. It illustrates that PdCl-based catalysts show donation of electrons from support to Pd nanoparticles, which is not observed in PdN-based catalysts. Moreover, this effect is more evident in CNT. The smallest and well-dispersed Pd nanoparticles (NPs) on PdCl/CNT with high electron density favor an excellent and stable activity and a remarkable selectivity to olefins. In contrast, the other three catalysts show lower selectivity to olefins and lower activities which suffer strong deactivation due to the formation of Pd carbides on their larger Pd nanoparticles with lower electron density, compared to PdCl/CNT.

Photothermal Catalytic CO2 Conversion: Beyond Catalysis and Photocatalysis.

In recent years, the combination of both thermal and photochemical contributions has provided interesting opportunities for solar upgrading of catalytic processes. Photothermal catalysis works at the interface between purely photochemical processes, which involve the direct conversion of photon energy into chemical energy, and classical thermal catalysis, in which the catalyst is activated by temperature. Thus, photothermal catalysis acts in two different ways on the energy path of the reaction. This combined catalysis, of which the fundamental principles will be reviewed here, is particularly promising for the activation of small reactive molecules at moderate temperatures compared to thermal catalysis and with higher reaction rates than those attained in photocatalysis, and it has gained a great deal of attention in the last years. Among the different applications of photothermal catalysis, CO2 conversion is probably the most studied, although reaction mechanisms and photonic-thermal synergy pathways are still quite unclear and, from the reaction route point of view, it can be said that photothermal-catalytic CO2 reduction processes are still in their infancy. This article intends to provide an overview of the principles underpinning photothermal catalysis and its application to the conversion of CO2 into useful molecules, with application essentially as fuels but also as chemical building blocks. The most relevant specific cases published to date will be also reviewed from the viewpoint of selectivity towards the most frequent target products.

Dynamics of Pd Subsurface Hydride Formation and Their Impact on the Selectivity Control for Selective Butadiene Hydrogenation Reaction.

Structure-sensitive catalyzed reactions can be influenced by a number of parameters. So far, it has been established that the formation of Pd-C species is responsible for the behavior of Pd nanoparticles employed as catalysts in a butadiene partial hydrogenation reaction. In this study, we introduce some experimental evidence indicating that subsurface Pd hydride species are governing the reactivity of this reaction. In particular, we detect that the extent of formation/decomposition of PdHx species is very sensitive to the Pd nanoparticle aggregate dimensions, and this finally controls the selectivity in this process. The main and direct methodology applied to determine this reaction mechanism step is time-resolved high-energy X-ray diffraction (HEXRD).

Photobio-electrocatalytic production of H2 using fluorine-doped tin oxide (FTO) electrodes covered with a NiO-In2S3 p-n junction and NiFeSe hydrogenase.

Clean energy vectors are needed towards a fossil fuel-free society, diminishing both greenhouse effect and pollution. Electrochemical water splitting is a clean route to obtain green hydrogen, the cleanest fuel; although efficient electrocatalysts are required to avoid high overpotentials in this process. The combination of inorganic semiconductors with biocatalysts for photoelectrochemical H2 production is an alternative approach to overcome this challenge. N-type semiconductors can be coupled to a co-catalyst for H2 production in the presence of a sacrificial electron donor in solution, but the replacement of the latter with an electrode is a challenge. In this work we attach a NiFeSe-hydrogenase with high activity for H2 production with the n-type semiconductor indium sulfide, which upon visible irradiation is able to transfer its excited electrons to the enzyme. In order to enhance the transfer of the generated holes towards the electrode for their replenishment, we have explored the inclusion of a p-type material, NiO, to induce a p-n junction for H2 production in a photoelectrochemical biocatalytic system in absence of sacrificial reagents.

Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1- x Fex )3 O4 Spinels.

Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn3 O4 to Mn2 O3 limits efficiency. In contrast, (Mn1- x Fex )3 O4 oxides show an enhanced transformation rate, but fundamental understanding of the role played by Fe cations is lacking. Here, nanoscale characterization of Fe-doped Mn oxides is performed to elucidate how Fe incorporation influences solid-state transformations. X-ray diffraction reveals the presence of two distinct spinel phases, cubic jacobsite and tetragonal hausmannite for samples with more than 10% of Fe. Chemical mapping exposes wide variation of Fe content between grains, but an even distribution within crystallites. Due to the similarities of spinels structures, high-resolution scanning transmission electron microscopy cannot discriminate unambiguously between them, but Fe-enriched crystallites likely correspond to jacobsite. In situ X-ray absorption spectroscopy confirms that increasing Fe content up to 20% boosts the reoxidation rate, leading to the transformation of Mn2+  in the spinel phase to Mn3+ in bixbyite. Extended X-ray absorption fine structure shows that FeO length is larger than MnO, but both electron energy loss spectroscopy and X-ray absorption near edge structure indicate that iron is always present as Fe3+  in octahedral sites. These structural modifications may facilitate ionic diffusion during bixbyite formation.

Biocide mechanism of highly efficient and stable antimicrobial surfaces based on zinc oxide-reduced graphene oxide photocatalytic coatings.

Highly efficient photoactive antimicrobial coatings were obtained using zinc oxide-reduced graphene oxide nanocomposites (ZnO-rGO). Their remarkable antibacterial activity and high stability demonstrated their potential use for photoactive biocide surfaces. The ZnO-rGO nanocomposites were prepared by the sol-gel technique to create photocatalytic surfaces by spin-coating. The coatings were deeply characterised and several tests were performed to assess the antibacterial mechanisms. rGO was homogeneously distributed as thin sheets decorated with ZnO nanoparticles. The surface roughness and the hydrophobicity increased with the incorporation of graphene. The ZnO-rGO coatings exhibited high activity against the Gram-positive bacterium Staphylococcus aureus. The 1 wt% rGO coated surfaces showed the highest antibacterial effect in only a few minutes of illumination with up to 5-log reduction in colony forming units, which remained essentially free of bacterial colonization and biofilm formation. We demonstrated that these coatings impaired the bacterial cells due to cell membrane damage and intracellular oxidative stress produced by the photogenerated reactive-oxygen species (ROS). The enhancement of the ZnO photocatalytic performance upon rGO incorporation is due to the increased detected generation of hydroxyl radicals, attributed to the reduction of electron-hole pair recombination. This intimate contact between both components also conveyed stability against zinc leaching and improved the coating adhesion.

Potentiometric detection of ATP based on the transmembrane proton gradient generated by ATPase reconstituted on a gold electrode.

Adenosine triphosphate (ATP) is a key molecule as energy vector for living organisms, therefore its detection reveals the presence of microbial colonies. Environments where the existence of microbial pathogens suppose a health hazard can benefit from real time monitoring of such molecule. We report a potentiometric biosensor based on ATP-synthase from Escherichia coli reconstituted in a floating phospholipid bilayer over gold electrodes modified with a 4-aminothiophenol self-assembled monolayer. The use of a pH-dependent redox probe on the electrode surface allows a simple, specific and reliable on site determination of ATP concentration from 1 µM to 1 mM. The broad range ATP biosensor can offer an alternative way of measuring in a few minutes the presence of microbial contamination.

High-Performance Photocatalytic Hydrogen Production and Degradation of Levofloxacin by Wide Spectrum-Responsive Ag/Fe3O4 Bridged SrTiO3/g-C3N4 Plasmonic Nanojunctions: Joint Effect of Ag and Fe3O4.

Highly photoresponsive semiconductor photocatalysis for energy and environmental applications require judicious choice and optimization of semiconductor interfaces for wide spectral capabilities. This work aims at rational designing of highly active SrTiO3/g-C3N4 junctions bridged with Ag/Fe3O4 nanoparticles for utilizing Z-scheme transfer and surface plasmon resonance effect of Ag augmented by iron oxide. The SrTiO3/(Ag/Fe3O4)/g-C3N4 (SFC) catalyst was employed for photocatalytic hydrogen production and photodegradation of levofloxacin (LFC; 20 mg/L) under UV, visible, near infra-red, and natural solar light exhibiting high performance. Under visible light (<780 nm), SFC-3 sample (30 wt % g-C3N4 and 3% Ag/Fe3O4) shows a H2 evolution of 2008 µmol g-1 h-1 which is ∼14 times that of bare g-C3N4. In addition, 99.3% removal of LFC was degraded in 90 min under visible light with retention of activity under sun. The inherent topological properties, complete, higher charge separation, and reduced recombination allowed this catalyst for a high photocatalytic response which was proved by UV-diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy, and photocurrent response measurements. Scavenging experiments and electron spin resonance analysis reveal that the mechanism shifts from a dual charge transfer in case of binary junction to essential Z-scheme with incorporation of Ag/Fe3O4. Both •O2- and •OH are main active radicals in visible light, whereas •O2- majorly participate under UV. The synergistic effect of SrTiO3, g-C3N4, and plasmon resonance of Ag/Fe3O4 not only improves light response and reduce recombination but also enhances the redox-ability of charge carriers. A H2 production mechanism and LFC degradation pathway (degradation, defluorination, and hydrolysis) has been predicted. This work paves a way for development of photocatalysts working in practical conditions for pollution and energy issues.

Role of Exposed Surfaces on Zinc Oxide Nanostructures in the Catalytic Ethanol Transformation.

For a series of nanometric ZnO materials, the relationship between their morphological and surface functionalities and their catalytic properties in the selective decomposition of ethanol to yield acetaldehyde was explored. Six ZnO solids were prepared by a microemulsion-precipitation method and the thermal decomposition of different precursors and compared with a commercial sample. All these materials were characterized intensively by XRD and SEM to obtain their morphological specificities. Additionally, surface area determinations and IR spectroscopy were used to detect differences in the surface properties. The density of acid surface sites was determined quantitatively using an isopropanol dehydration test. Based on these characterization studies and on the results of the catalytic tests, it has been established that ZnO basal surfaces seem to be responsible for the production of ethylene as a minor product as well as for secondary reactions that yield acetyl acetate. Furthermore, one specific type of exposed hydroxyl groups appears to govern the surface catalytic properties.

Morphological and structural behavior of TiO2 nanoparticles in the presence of WO3: crystallization of the oxide composite system.

Composite TiO2-WO3 oxide materials were prepared by a single pot microemulsion method and studied during calcination treatments under dry air in order to analyze the influence of tungsten on the behavior of the dominant titania component. To this end, the surface and bulk morphological and structural evolution of the solid precursors was studied using X-ray diffraction and infrared spectroscopy. In the calcination process, differences in the dominant titania component behavior appeared as a function of the W/Ti atomic ratio of the precursor. First, the crystallization of the anatase phase is affected by tungsten through an effect on the primary particle size growth. Furthermore, such an effect also influences the anatase to rutile phase transformation. The study provides evidence that the W-Ti interaction develops differently for a low/high W/Ti atomic ratio below/above 0.25 affecting fundamentally the above-mentioned anatase primary particle size growth process and the subsequent formation of the rutile phase and showing that addition of tungsten provides a way to control morphology and phase behavior in anatase-based oxide complex materials.

Influence of the Ce-Zr promoter on Pd behaviour under dynamic CO/NO cycling conditions: a structural and chemical approach.

The behaviour of the Pd phase in three way catalysts (TWCs) having a Ce-Zr oxide as a promoter component has been examined under CO/NO cycling conditions. In order to extract information on the role of the noble metal and the metal-promoter interface, two catalysts in, respectively, the presence or the absence of the promoter and having a similar Pd particle size were analyzed by a synchronous multitechnique approach using X-ray absorption (XAS) or high energy X-ray diffraction (HXRD) in combination with diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS). From a structural point of view it is shown that the promoter oxide strongly influences Pd behaviour, limiting morphological (size/shape) and structural (formation of carbide/oxide phases) modifications occurring under dynamic conditions in the absence of the promoter. Activity measurements show that these phenomena have important chemical consequences in terms of CO/NO pollutant metal coverage(s), the occurrence of NO and/or CO dissociation steps as well as the subsequent transformation of the pollutants into CO2 and N2.

Nanoparticulate Pd supported catalysts: size-dependent formation of Pd(I)/Pd(0) and their role in CO elimination.

A combination of time-resolved X-ray absorption spectroscopy (XAS), hard X-ray diffraction (HXRD), diffuse reflectance infrared spectroscopy (DRIFTS), and mass spectrometry (MS) reveals a series of size-dependent phenomena at Pd nanoparticles upon CO/(NO+O(2)) cycling conditions. The multitechnique approach and analysis show that such size-dependent phenomena are critical for understanding Pd CO elimination behavior and, particularly, that different Pd(I) and Pd(0) centers act as active species for a size estimated by XAS to be, respectively, below and above ca. 3 nm. The relative catalytic performance of these two noble metal species indicates the intrinsic higher activity of the Pd(I) species.

The behavior of mixed-metal oxides: physical and chemical properties of bulk Ce1-xTbxO2 and nanoparticles of Ce1-xTbxOy.

The physical and chemical properties of bulk Ce(1-x)Tb(x)O(2) and Ce(1-x)Tb(x)O(y) nanoparticles (xTb exchange nor the introduction of oxygen vacancies in Ce(1-x)Tb(x)O(y) significantly affect the charge on the Ce cations. In contrast, the O K-edge and Tb L(III)-edge XANES spectra for Ce(1-x)Tb(x)O(y) nanoparticles show substantial changes with respect to the corresponding spectra of Ce and Tb single oxide references. The Ce(0.5)Tb(0.5)O(y) compounds exhibit a much larger Tb(3+)/Tb(4+) ratio than TbO(1.7). A comparison with the properties of Ce(1-x)Zr(x)O(y) and Ce(1-x)Ca(x)O(y) shows important differences in the charge distribution, the magnitude of the dopant induced strain in the oxide lattice, and a superior behavior in the case of the Ce(1-x)Tb(x)O(y) systems. The Tb-containing oxides combine stability at high temperature against phase segregation and a reasonable concentration of O vacancies, making them attractive for chemical and catalytic applications.