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A spectroscopic and microscopic investigation was made of the dynamics of bimetallic nanoparticles (NPs) in Co–Ni/MgAl2O4 catalysts used for the steam reforming of ethanol (SRE) reaction, consideri...

We focus herein on understanding how the oxidation mechanism of glucose may be affected by the nature of the surface facets of Cu2O-based electrocatalytic sensors. To this end, we performed a series of in situ FTIR spectroelectrochemical experiments and DFT simulations by employing Cu2O cubes and octahedra as electrocatalytic sensors for glucose and other interferents. Interestingly, our in situ results demonstrated that the glucose oxidation mechanism displayed shape-dependent behavior, indicating that the glucose molecule can selectively adsorb on the Cu2O {1 0 0} facets relative to ascorbate and urate interferents in a process that probably occurs without the need for an external potential. However, when the same reaction was performed in the presence of Cu2O octahedra ({1 1 1} facets), the reaction was not selective, and the final product remained on the surface, blocking the sites for further glucose oxidation and leading to significantly lower electrocatalytic activities. Surprisingly, no bands related to the formation of Cu3+ species were detected, indicating that Cu3+ species do not participate in the reaction mechanism. This is very important because these species have been assumed to be the catalytically active sites for glucose oxidation. We believe that the results presented herein provide new insights into different aspects of the oxidation of carbohydrates and may inspire a deeper mechanistic investigation of other semiconductor materials and the development of optimized electrocatalysts.

The palladium(II)-mediated chemical uncaging reaction of propargylic substrates is a recent addition to the field of chemical biology and medicinal chemistry in the activation of bio and prodrug mo...

Deposition on the surface of amberlite resin was conducted to produce two different types of bimetallic nanoparticles, combining one of three different metals (M = Cu, Ag and Ni) with Pd (M–Pd@R and Pd–M@R). To obtain the bimetallic nanoparticles, the four different metal ions were firstly immobilized on the resin surface by ion exchange and monometallic nanoparticles were formed by reduction of the metal ions with NaBH4. By changing the sequence of metal ion immobilization on the resin, six bimetallic supported catalysts were prepared. Surface oxidation of the metals on the surface layer is inhibited in some cases and the catalytic propensity for certain reactions is improved. After careful characterization by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption near edge structure, the activity of the catalysts was evaluated performing kinetic studies on the reduction reactions of 4-nitrophenol and phenylacetylene. The kinetic study revealed that the geometric factor, opening up catalyst sites through the ensemble effect, seems to be the main reason for the differentiated catalytic activity of the nanoparticle composites. Moreover, high selectivity for styrene in the hydrogenation of phenylacetylene was observed for Cu-containing catalysts, with almost total conversion of the substrate.

We report the optimization of both the support and the active phase of PdPt NPs supported on TiO2 nanowires to obtain highly active electro/photocatalysts for the oxygen reduction and water splitting reactions. This system displayed strong metal-support interactions, high concentration of oxygen vacancies, and PdPt NP were similar to 2 nm in size. By optimizing the loading of PdPt, both the photo- and electrocatalytic activities were improved compared to commercial materials. Interestingly, a volcano plot was obtained from the activity and the PdPt composition, and the Pd0.22P0.78-TiO2/C sample afforded the optimal performance. For instance, the amount of hydrogen produced from water splitting was 11.6 mmol/g(catalyst). For the ORR, the activity was similar to a commercial Pt catalyst, but a lower E-onset (0.87 V-RHE vs w 0.95 V-RHE) was detected. The variations in the activities with the composition correlated well with the variations in the electronic effects and the concentration of oxygen vacancies.

By a combination of theoretical and experimental design, we unraveled the effect of {111} and {100} surface facets on the electrocatalytic sensing activities and stabilities of metal oxides by employing Cu2O crystals as a model substrate and glucose as the analyte. We started by theoretically investigating the potential energy curves for the glucose interaction with the Cu2O {111} and {100} surface facets. We found that the glucose interaction energy was significantly higher for the {100} facets than for the {111} facets. Then, we experimentally observed that their electrocatalytic sensing performance displayed shape-dependent behavior. While the catalytic activities followed the order cubes > cuboctahedrons > octahedrons, their stabilities showed the opposite trend. The higher catalytic activity enabled by the {100} facets is explained by their stronger interaction with glucose. On the other hand, the higher stability allowed by the {111} facets is justified by their lower concentration of oxygen vacanci...

We described herein the facile synthesis of sub-15 nm CeO2 nanowires based on a hydrothermal method without the use of any capping/stabilizing agent, in which an oriented attachment mechanism took place during the CeO2 nanowire formation. The synthesis of sub-15 nm CeO2 nanowires could be achieved on relatively large scales (∼2.6 grams of nanowires per batch), in high yields (>94%), and at low cost. To date, there are only a limited number of successful attempts towards the synthesis of CeO2 nanowires with such small diameters, and the reported protocols are typically limited to low amounts. The nanowires displayed uniform shapes and sizes, high surface areas, an increased number of oxygen defects sites, and a high proportion of Ce3+/Ce4+ surface species. These features make them promising candidates for oxidation reactions. To this end, we employed the selective oxidation of aniline as a model transformation. The sub-15 nm CeO2 nanowires catalyzed the selective synthesis of nitrosobenzene (up to 98% selectivity) from aniline at room temperature using H2O2 as the oxidant. The effect of solvent and temperature during the catalytic reaction was investigated. We found that such parameters played an important role in the control of the selectivity. The improved catalytic activities observed for the sub-15 nm nanowires could be explained by: i) the uniform morphology with a typical dimension of 11 ± 2 nm in width, which provides higher specific surface areas relative to those of conventional catalysts; ii) the significant concentration of oxygen vacancies and high proportion of Ce3+/Ce4+ species at the surface that represent highly active sites towards oxidation reactions; iii) the crystal growth along the (110) highly catalytically active crystallographic directions, and iv) the mesoporous surface which is easily accessible by liquid substrates. The results reported herein demonstrated high activities under ambient conditions, provided novel insights into selectivities, and may inspire novel metal oxide-based catalysts with desired performances.

The main purpose of this work is to contribute to the description of the acetone synthesis from ethanol employing Zn x Zr 1-x O 2-y based catalysts. The catalytic behavior of these solids was evaluated (isoconversion) in the acetone synthesis. The most active catalyst and m -ZrO 2 (used as a reference) were characterized by the following techniques: pyridine adsorption, TPD of NH 3 , TPD of CO 2 , TPD of ethanol followed by IR (DRIFTS)/MS, TPD of ethanol followed by XANES at the Zr K-edge and Zn K-edge and XRD in situ . The present study suggests that the main steps of the acetone generation from ethanol are the following: firstly, ethoxide species are generated and, then, they are dehydrogenated to acetaldehyde. Both steps are related to strong basic and acid sites. Acetaldehyde reacts with the O of the solid solution generating acetate species and vacancies on the catalyst surface. These carboxylate species condensate (strong basic sites) and generate acetone and CO 2 . Water dissociates on the vacancies of the catalyst and reoxidizes the its surface, closing the catalytic cycle. All these steps might occur on Zn +2 and on the species in its vicinity (XANES).

The effect of ceria in cobalt-ceria-alumina catalyst was studied using in situ X-ray near edge spectroscopy (XANES) at Co K-edge and Ce LIII-edge. The introduction of ceria in this catalyst resulted in a significant removal of Co from CoAl2O4 spinel phase to Co and CoO phases. The Co K-edge revealed the symmetry changes in Co according to the temperature and atmosphere in reduction process. We also showed the stability of Co sites as well the oxidation state of ceria in operando steam reforming of ethanol (SRE) reaction. After reduction of Ce4+ to Ce3+, no significant changes were observed by XANES. Gas Chromatography (GC) analysis showed a high ethanol conversion at 500 °C, high hydrogen yield and low formation of undesired products as methane and ethylene. The results showed a Co/Ce/Al2O3 catalyst as promising material to be applied in hydrogen production in SRE reaction.

The trans-2-phenylvinylboronic acid homocoupling reaction catalyzed by palladium nanocubes (Pd-NCs) was investigated by kinetics, spectroscopy, and poisoning experiments. The reaction was evidenced to be sensitive to the presence of the base, which acts synergistically with the substrate molecules and assists the leaching of Pd oxide (PdOx) species to the reaction medium. This species catalyzes the homocoupling reaction through the formation of Pd–Ox–B(OH)2R pretransmetalation intermediates, via coordination with the vinylboronic acid molecules, involving an oxo-palladium-type interaction. The reaction rate was not enhanced by the saturation of the reaction medium with O2, which is due to the oxidized nature of the Pd-NC surface.

A mechano-colloidal approach was developed to produce Au nano-tadpoles. It comprises the generation of seeds by ball-milling from a solid mixture containing a precursor, reductant, and capping agent, followed by the dispersion of this mixture in water leading to seeded-growth to generate the target nanoparticle morphology.

Pt nanoparticles (Pt NPs) supported on carbon have been widely employed as electrocatalysts toward oxygen reduction reaction. The development of more efficient electrocatalysts that enable one to reduce or even not require the use of Pt is a central challenge. In addition to the control over the physical and chemical features of Pt NPs, metal support interactions can be employed to enhance activities via the generation and exposure of surface-active sites. In this context, we report herein the development of electrocatalysts composed of Pt NPs supported on TiO2 microspheres, that were subsequently impregnated onto carbon. We have found that, by optimizing the loading of Pt at the TiO2 surface, the electrocatalytic activity toward the ORR could be improved compared to that of the commercial Pt/C (E-TEK) material, even at lower Pt loadings. The enhancement in activities could be assigned to the balance between Pt loading and generation of reactive surface sites, such as adsorbed oxygenated species. Moreover, the utilization of TiO2 as support enabled improved stabilities relative to Pt/C (E-TEK). We believe that the results described herein may inspire the development of electrocatalysts for the ORR with improved activities and stabilities.

Gold nanoparticles incorporated on ceria nanowires have been employed as efficient nanocatalysts for the selective oxidation of thioanisole. The control of both physical and chemical parameters as well as metal–support interactions are important factors that determine their performances. Considering their one-dimensional morphology with large surface area, thin diameters, high concentration of oxygen vacancies, and small Au NPs uniformly on the entire CeO2 surface with a high fraction of oxidized gold species, these characteristics make them favorable nanocatalysts for oxidation transformations. The CeO2-Au nanowires displayed improved performances towards the oxidation of thioanisole when compared to the pure CeO2 nanowires and commercial CeO2-Au catalysts. The CeO2-Au nanowires catalyzed the selective synthesis of methyl phenyl sulfoxide with up to 100 % of selectivity and high conversion. The impact of solvent and temperature during the catalytic reaction was also experimentally and theoretically investigated by DFT calculations, indicating a key role in the observed activities.

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.

This study demonstrates that the precursor reduction kinetics can be employed to control the morphology and composition of bimetallic metal/metal oxides systems obtained by galvanic replacement reaction using metal oxides as sacrificial templates. This work investigated Cu2O as a proof-of-concept example, in which the relative rates of Cu2O oxidation by O2 and by noble metal precursors determined the morphology and composition of the products. We focused on three metal precursors with fast, medium, and slow reduction kinetics in the presence of Cu2O under aerobic conditions: PdCl42–, AuCl4–, and Ru3+, respectively. It was found that metal-oxide-based bowls, rattles, or dendrites can be obtained by simply changing the precursor reduction kinetics. These results provide novel insights over the versatility and mechanistic understanding of galvanic replacement to the synthesis of metal/metal-oxide bimetallic nanoparticles.

Although green catalytic transformations are very attractive, they often remain limited by low conversion percentages and selectivity. Here, we demonstrate that high catalytic performances (TOF = 590,000 h −1 ) could be achieved towards the green oxidation of silanes and H 2 production under ultralow Au loadings (0.001–0.0002 mol% in terms of Au) employing H 2 O as the oxidant, 25 °C as the reaction temperature, and MnO 2 nanowires decorated with ultrasmall Au NPs (3 nm) as catalysts. In addition to these high activities towards a variety of substrates, the MnO 2 –Au NPs displayed good stability/recyclability, in which no morphological changes or loss of activity were observed even after 10 reaction cycles. The improved catalytic activities observed for the MnO 2 –Au NPs can be assigned to: (i) the metal–support interactions, in which the presence of Au NPs could facilitate oxidative processes and thus yield high performances towards the oxidation of hydrosilanes; (ii) the significant concentration of Au δ+ species and oxygen vacancies at the catalyst surface that represent highly catalytically active sites towards oxidation reactions, and (iii) the Au NPs ultrasmall sizes at the MnO 2 surface that enable the exposure of high energy Au surface/facets, high surface-to-volume ratios, and their uniform dispersion. The MnO 2 –Au NPs could be synthesized by a facile approach based on the utilization of MnO 2 nanowires as physical templates for Au deposition without any prior surface modification/functionalization steps. The utilization of supported ultrasmall Au NPs having controlled sizes and dispersion may inspire the design of novel catalysts capable of enabling high catalytic performances towards green transformations at ultralow metal loadings.