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Levulinic acid is an important molecule of biomass and the gamma-valerolactone (GVL) is one of the most promising compound from levulinic acid. We have developed an efficient catalyst for the catalytic conversion of LA into GVL, ruthenium based catalyst in silica, titania and a silica-titania hybrid support The prepared catalysts were characterized by TEM, XRD, TPR and nitrogen adsorption analysis. The results have shown higher catalytic activity of Ru/TiO2-SiO2 than Ru/TiO2 either Ru/SiO2. Herein, we report that yields higher than 90% were obtained for gamma-valerolactone from levulinic acid hydrogenation catalyzed by Ru/TiO2-SiO2 at 100 °C and 20 atm of hydrogen without additives.

We reported herein a systematic investigation on how the nature of the support affected the catalytic performances of Rh nanoparticles. The prepared catalysts were denoted as Rh/MxOy, where M corresponded to Ce, Ti, Si, Zn, and Al, and Rh was Rh3+ reduction to Rh nanoparticles on the surface of oxides. This strategy was performed in a single step using urea as a mediator and in the absence of any other stabilizer or capping agent. The Rh nanoparticles displayed relatively similar sizes, shapes, and uniform distribution over the supports, differing only in terms of the nature of the support. This strongly affected the metal–support interaction between Rh nanoparticles and the respective oxides, leading to significant differences in their catalytic performances toward the ethanol steam reforming. Here, not only the catalytic activity (in terms of ethanol conversion) was affected, but both the selectivity and stability were also influenced by the nature of the oxide support. Interestingly, the reaction paths as well as the deactivation profile were completely changed as function of the employed support. Such differences were associated with differences in the oxygen storage, oxygen mobility, and acidity/basicity of the supports. We believe that our results can contribute to the development and understanding of Rh-supported catalysts for the applications toward gas-phase transformations such as the ethanol steam reforming reaction.

We reported herein the synthesis in high yields (>97%) of Ce0.9Sm0.1O2-δ nanowires displaying well-defined shape, size, and composition by a simple, fast, and low-cost two-step hydrothermal method. The Ce0.9Sm0.1O2-δ nanowires synthesis was followed by the wet impregnation of Ni without the utilization of any stabilizing agent. The Ni/Ce0.9Sm0.1O2-δ nanowires showed higher surface area, high concentration of oxygen vacancies at surface, and finely dispersed Ni particles with significantly higher metallic surface area as compared with catalysts prepared from commercial materials with similar compositions. Such unique and improved properties are reflected on the catalytic performance of the Ni/Ce0.9Sm0.1O2-δ nanowires towards ethanol steam reforming. The nanowires exhibited high yields for hydrogen production (∼60% of selectivity) and an exceptional stability with no loss of activity after 192 h of reaction at 550 °C. The reported results provide insights and can inspire high-yield production of nanostructured catalysts displaying controlled and superior properties that enable practical applications in heterogeneous catalysis.

The understanding of relaxation dynamics of metallic nanoshells is important for a range of nanotechnological applications. In this work, we present a combined experimental-theoretical study of the relaxation dynamics of AgAu nanoshells. This was investigated using ultrafast pump-probe experiments resonant with the surface plasmon of the nanoshells, as well as via atomistic molecular dynamics simulations of relaxation and temperature-jump (DT-jump) processes. Both techniques were then discussed and complemented using a non-equilibrium statistical mechanical model. Data collected at low energies were consistent with our previously reported work and allowed the characterization of intrinsic electron-phonon coupling times (EPCT) and of the overall relaxation dynamics in terms of a two-temperature model. Data at intermediate and higher energies, in turn, showed a nonlinear dependence of EPCT as a function of the pump power, faster relaxation being observed at higher pump energies. In the limit of small DT-jumps, relaxation based on a two-temperature model is recovered, whereas in the limit of large DT-jumps, the relaxation becomes faster with increasing temperature change. The results reported here give insight on the ultrafast dynamics of AgAu nanoshells and might also be applied to other metallic systems, paving the way to the better understanding of relaxation dynamics of nanoparticles in general.

We reported the organic template-free synthesis of gold (Au) nanoparticles (NPs) supported on TiO2, SiO2, and Al2O3 displaying uniform Au sizes and high dispersions over the supports. The Au-based catalysts were prepared by a deposition–precipitation method using urea as the precipitating agent. In the next step, the solvent-free oxidation of benzyl alcohol was investigated as model reaction using only 0.08–0.05 mol% of Au loadings and oxygen (O2) as the oxidant. Very high catalytic performances (TOF up to 443,624 h−1) could be achieved. Specifically, we investigated their catalytic activities, selectivity, and stabilities as well as the role of metal–support interactions over the performances. The conversion of the substrate was found to be associated with the nature of the employed support as the Au NPs presented similar sizes in all materials. A sub-stoichiometric amount of base was sufficient for the catalyst activation and the observation of the catalysts profile over the time enable insights on their recyclability performances. We believe this reported method represents a facile approach for the synthesis of uniform Au-supported catalysts displaying high performances.

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.

Plasmonic catalysis takes advantage of the surface plasmon resonance (SPR) excitation to drive or accelerate chemical transformations. In addition to the plasmonic component, the control over metal-support interactions in these catalysts is expected to strongly influence the performances. For example, CeO2 has been widely employed towards oxidation reactions due to its oxygen mobility and storage properties, which allow for the formation of Ce3+ sites and adsorbed oxygen species from metal-support interactions. It is anticipated that these species may be activated by the SPR excitation and contribute to the catalytic activity of the material. Thus, a clear understanding of the role played by the SPR-mediated activation of surface oxide species at the metal-support interface is needed in order to take advantage of this phenomenon. Herein, we describe and quantify the contribution from active surface oxide species at the metal-support interface (relative to O2 from air) to the activities in green SPR-mediated oxidation reactions. We employed CeO2 decorated with Au NPs (Au/CeO2) as a model plasmonic catalyst and the oxidation of p-aminothiophenol (PATP) and aniline as proof-of-concept transformations. We compared the results with SiO2 decorated with Au NPs (Au/SiO2), in which the formation of surface oxide species at the metal-support interface is not expected. We found that the SPR-mediated activation of surface oxide species at the metal-support interface in Au/CeO2 played a pivotal role in the detected activities, being even higher than the contribution coming from the activation of O2 from air.

Here, we have systematically investigated how the nature of the support influenced the oxygen mobility and activities in catalysts comprised of AgPt nanoshells deposited over inorganic oxides. We first synthesized AgPt nanoshells by galvanic replacement reaction between Ag nanospheres and PtCl6 2− (aq) combined with Pt reduction using hydroquinone as an auxiliary reducing agent. The nanoshells were then supported over TiO2, Al2O3 and CeO2. Through this methodology, we prepared materials with similar metallic nanoparticle AgPt compositions (~0.99 wt% Pt), sizes (43 ± 2 nm diameter), spherical shapes, surface morphologies, number of active sites $$ (\sim4.5\;\upmu{\text{mol}}\;{\text{g}}_{{{\text{cat}} .}}^{ - 1} ) $$ and uniform distribution over the supports, differing only in terms of the nature of the support. The oxide reduction temperature, its capability of re-oxidation and the presence of oxygen mobility were strongly dependent on the metal–support interaction between AgPt nanoshells and oxide supports. These properties have significantly influenced their catalytic performances toward the CO oxidation. At 230 °C, the CO oxidation TOF was 40.4 ± 0.4, 6.9 ± 1, 1.4 ± 0.8 min−1 for AgPt/CeO2, AgPt/TiO2, AgPt/Al2O3, respectively. These differences were attributed to the concentration of oxygen vacancies in each catalyst, which presented exactly the same trend as that of the catalytic activities. Our results may have important contributions to the design of highly active metal oxide-based catalysts toward gas-phase oxidation transformations.

Undergraduate-level laboratory experiments that involve the synthesis of nanomaterials with well-defined/controlled shapes are very attractive under the umbrella of nanotechnology education. Herein we describe a low-cost and facile experiment for the synthesis of Cu(OH)2 and CuO nanowires comprising three main parts: (i) synthesis of Cu(OH)2 nanowires by a precipitation approach followed by a calcination step that converts Cu(OH)2 to CuO; (ii) use of Cu(OH)2 and CuO nanowires as model systems to explore a variety of characterization techniques relevant in the context of solid-state chemistry, materials chemistry, and nanoscience; and (iii) presentation/discussion of the data. Other learning objectives include probing of chemical transformations at the nanoscale and the use of concepts borrowed from coordination chemistry to understand the formation mechanism of Cu(OH)2 and CuO nanowires from a Cu2+(aq) precursor. This experiment can be performed with a relatively simple laboratory infrastructure and with ...

Metallic nanoparticles have been extensively studied towards applications in catalysis. Among the several methods for their controlled synthesis, galvanic replacement is particularly attractive as it enables the production of bimetallic and hollow nanomaterials displaying ultrathin walls in a single reaction step. This procedure is versatile, but final morphologies are often limited to shapes that represent the hollow analogues of the starting template nanocrystals. For catalytic applications, it is highly desirable to broaden the scope of physicochemical control that can be achieved by this method. This feature article discusses recent strategies developed in our group for the synthesis of hollow bimetallic nanomaterials by galvanic replacement that enable a further level of control over surface morphologies and composition. We begin by briefly explaining the fundamentals of the conventional galvanic replacement reaction between Ag and AuCl4-. This is one of the most characteristic galvanic replacement reactions, and it can be tuned to create a huge variety of nanoparticle morphologies. We will discuss how advanced electron microscopy characterization enables us to uncover surface-segregation behavior as a function of compositions, and relate this to the detected catalytic performance. We will also discuss how galvanic replacement can be extended to trimetallic compositions, leading to improvements in catalytic activities compared to mono or bimetallic counterparts. Furthermore, we will show how surface morphology, size, and anisotropic growth can be controlled by tuning the temperature during the synthesis and by combining galvanic replacement reaction with co-reduction. Finally, we will demonstrate how these approaches are promising for large-scale synthesis of controlled hollow nanostructures and their incorporation into supports to produce catalysts at the gram-scale. We believe the developments described herein shed important insights and may inspire the development of sophisticated and controlled nanomaterials at relatively larger scales for catalytic applications.

Organophosphate (OP) detoxification is a worldwide problem due to the high stability of P–O bonds. Here, we designed several imidazole-coated nanocatalysts targeted towards the cleavage of OP and thus their detoxification. Specifically, Ag, Au and bimetallic AgAu nanoparticles (NPs) supported on SiO2 were functionalized with methimazole (MTZ), which comprises thiol and imidazole groups, foreseeing enabling freely available imidazole groups. Raman analyses indicate that MTZ interacts preferably via its sulfur atom over Au NPs and via the nitrogen of the imidazole ring over Ag NPs. The MTZ-derived nanocatalysts were effective towards OP cleavage. For instance, rate enhancements of 108 fold were obtained for the toxic pesticide Paraoxon, compared to the uncatalyzed reaction. Interestingly, Au-derived nanocatalysts were significantly more effective since the imidazole group is free to react with the OP, which is not possible when Ag–N interactions take place.

Noble-metal nanoparticles have been widely employed in catalysis. As catalytic properties are dependent on their physical/chemical parameters, strategies for their controlled synthesis and the understanding of performance relationships have gained attention. In this review, we discuss developments on well-defined noble-metal nanoparticles focusing on relationships between performance and physical/chemical features. We begin with the control over shape, composition, and size. Then, we focus on nanoparticles with hollow interiors, which provide further possibilities for performance optimization. We provide a case-by-case discussion to illustrate how, in addition to the hollow interiors, the control over their composition, size, and surface morphology relate to catalytic performance.

Mass diffusion controls material structuring from the atomic to the macro-scale defining properties and functionalities. We show here that surface energy in Ce0.9Gd0.1O3-d shaped nanocrystals, i.e. nanocubes, nanorods and spherical nanoparticles, can control solid state diffusion mechanisms over a long range, leading to extreme microstructural diversity.

A proteic sol-gel route was used in the production of NiMoO4 catalysts, which used edible gelatin as a precursor. The triple helix structure of a protein in contact with identical structures acquires an unfolded form, which favors the interaction of the reactive groups of the gelatin (NH3+ and COO−) with the metallic ions (MoO42− and Ni2+). The synthesized catalysts were thoroughly characterized using techniques such as X-ray diffraction, thermogravimetric and differential thermal analysis, Raman scattering, scanning and transmission electron microscopies, UV–Vis spectroscopy, and colorimetry. The results showed that it is possible to prepare the phase-pure α-NiMoO4 polymorph only at temperatures above 700 °C, while a mixture of the polymorphs α and β were obtained at lower temperatures. The synthesized materials calcined at 300, 500, and 700 °C have their catalytic potentials tested in the ethanol steam reforming reaction aiming the production of hydrogen and presented a good performance. The results indicated that among tested materials, the sample calcined at 700 °C exhibited the highest stability, activity, and best selectivity relative to the product of interest.

AgPd nanoshells (AgPd NSs) were used as dual catalysts for hydrogen production and reduction of organic compounds in a one-pot protocol. AgPd NSs were very efficient catalysts for the reduction of several functional groups, including alkenes, alkynes, imines, nitro compounds, and azides. Excellent chemoselectivities were observed for α,β-unsaturated ketones, esters, and cinnamonitrile. Also, deuterium-labeled compounds were prepared by using D2O instead of H2O. A packed-bed reactor containing the immobilized AgPd NSs in silica (AgPd/SiO2) was designed to be used in continuous-flow conditions. An optimized flow system with AgPd NSs was able to give the desired compounds in high conversions with 30–60 min residence time (tR).

We describe herein the synthesis of MgNiO 2 nanoparticles employing a new one-dimensional system [MgNi(opba)] n ·9 n H 2 O, with opba standing for ortho -phenylenebis(oxamato), as precursor. The MgNiO 2 nanoparticles could be obtained after heat-treatment at 800 °C for 5 h under air atmosphere, which was responsible for the elimination of water and organic precursor material leading the formation of nanoparticles with average size of 40±9 nm. To this end, we first described the synthesis of [MgNi(opba)] n ·9 n H 2 O chain, which was obtained using a pre-synthetized Na 2 [Ni(opba)]·5H 2 O and Mg 2+ (molar ratio of 1:1) in aqueous media and then this chain was calcined to produce the desired MgNiO 2 nanoparticles. The obtained MgNiO 2 nanoparticles showed good catalytic performance towards ethanol decomposition achieving 100% of substrate conversion and producing acetaldehyde (56.8%) and hydrogen (24.8%) as the main gaseous products. Also, carbon based structures of great interest for technological applications, carbon nanotubes and onions were formed as valuable byproducts. Thus, we believe that our reported results may inspire the synthesis of catalysts with improved performances for applications in other gas-phase transformations.

Bimetallic and asymmetric heterostructures represent an emerging class of nanomaterials. They allow for the combination of distinct compositions, shapes, and physicochemical features within a single particle, thus leading to intriguing properties. We demonstrate herein the synthesis of asymmetric Au@Pd-Au tadpoles having a tail comprising a single Au nanorod and a spherical head composed of core@shell Au@Pd decorated with small Au NPs. This material was produced by a combination of Au deposition and Ostwald ripening at the surface of Au@Pd core-shell NPs. The overall morphology could be tailored both by controlling the amount of AuCl4− employed as precursor and by altering the reaction time, leading to shape-dependent optical and catalytic properties. We believe that these results may have important implications for the synthesis nanomaterials having novel morphologies and complex functionalities that can combine properties from their different components.

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.

There is a growing interest in controlling the synthesis of colloidal metal nanocrystals and thus tailoring their properties toward various applications. In this context, choosing an appropriate combination of reagents (e.g., salt precursor, reductant, capping agent, and stabilizer) plays a pivotal role in enabling the synthesis of metal nanocrystals with diversified sizes, shapes, and structures. Here we present a comprehensive review that highlights one of the key reagents for the synthesis of metal nanocrystals via chemical reduction: the reductants. We start with a brief introduction to the compounds commonly employed as reductants in the colloidal synthesis of metal nanocrystals by showing their oxidation half-reactions and the corresponding oxidation potentials. Then we offer specific examples pertaining to the controlled synthesis of metal nanocrystals, followed by some fundamental aspects covering the general mechanisms of metal ion reduction based on the Marcus Theory. Afterwards, we present a case-by-case discussion on a wide variety of reductants, including their major properties, reduction mechanisms, and additional effects on the final products. We illustrate these aspects by selecting key examples from the literature and paying close attention to the underlying mechanism in each case. At the end, we conclude by summarizing the highlights of the review and providing some perspectives on future directions.

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 MnO

We describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au58@Pd42 > Au27@Pd73 > Ag20Pd80 and Ag8Pd92 > Au12@Pd88 > Ag38Pd62, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities.

The synthesis of trimetallic nanoparticles represents an emerging strategy to maximize catalytic performances in noble metal-based catalysts. However, the controllable synthesis of trimetallic nanomaterials as well as the exact role played by the addition of a third metal in their composition over catalytic performances remains unclear. In this paper, we describe the synthesis of trimetallic nanoshells having AgAuPd, AgAuPt, and AgPdPt compositions by a sequential galvanic replacement reaction approach between Ag nanospheres as sacrificial templates and the corresponding metal precursors, i.e., AuCl4 − (aq), PdCl4 2− (aq), and/or PtCl6 2− (aq). In each of these systems, the composition could be systematically tuned by varying the molar ratios between Ag and each metal precursor. Nanoshells having Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 compositions were employed as model systems to investigate the effect of the addition of the third metal in their composition over the catalytic activities toward the 4-nitrophenol reduction. Our data demonstrate a significant enhancement in conversion percentages and thus the catalytic activities relative to the sum of their bimetallic counterparts, and this increase was dependent on the nature of the metals, corresponding to 826, 135, and 56 % for Ag56Au28Pd16, Ag78Au9Pt13, and Ag71Pd16Pt13 nanoshells relative to their bimetallic analogs. The results presented herein demonstrate the strong correlation between catalytic activity and composition in multimetallic nanoshells, and that the incorporation of a third metal may represent a promising approach to boost catalytic activities for a variety of transformations.

Two novel automated methods for the determination of surface roughness and chemical distribution in individual nanoparticles are presented and applied to nanoparticles synthesised by the galvanic replacement reaction. The two methodologies apply the determination of circumferential and radial line profiles to determine surface roughness and elemental distribution respectively. The surface roughness analysis provides details on localised changes in roughness in comparison to single measures of circularity. The X-ray spectroscopic concentric ring scan outperforms conventional line scans when elemental distribution approximately possesses a spherical symmetry.

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.

We report herein the high yield synthesis of Cu 2 O spheres displaying well-defined shapes and monodisperse sizes that could be employed as the source of highly catalytic active Cu(I) species towards click reactions between several of alkynes and azides to produce a variety of 1,2,3-triazoles under ligand-free and ambient conditions (in an open reactor). The utilization of Cu 2 O spheres enabled superior performance as compared to a conventional protocol in which CuSO 4 is employed in combination with sodium ascorbate as the catalyst system. In addition, the compounds were obtained in synthetically useful yields, and seven of them have not been previously reported. We believe the results reported herein shed new insights into the optimization of activity and versatility of click reactions towards the synthesis of target molecules in environmentally friendly conditions.

International audience; Mono and bimetallic catalysts based on Pt and Pd were prepared by a co-precipitation method. They were tested in liquid phase hydrogenation reactions of glucose and furfural at low temperature and pressure. The bimetallic PtPd/TiO2 catalyst proved to be an efficient material in selectively hydrogenating glucose to sorbitol. Moreover, high furfural conversion was attained under relatively soft conditions, and the furfuryl alcohol selectivity was strongly affected by the chemical composition of the catalysts. Furfuryl alcohol (FA) was the major product in most cases, along with side products such as methylfuran (MF), furan, and traces of tetrahydrofuran (THF). These results showed that the PtPd bimetallic sample was more active relative to the monometallic counterparts. A correlation between the catalytic results and the physicochemical properties of the supported nanoparticles identified key factors responsible for the synergetic behavior of the PtPd system. The high activity and selectivity were due to the formation of ultra-small particles, alloy formation, and the Pt-rich surface composition of the bimetallic particles supported on the TiO2 nanowires.

This study describes the applicability of two chemically modified sugarcane bagasses containing either adsorbed Co2+ or Cr3+ ions as heterogeneous catalysts for the autooxidation of monoterpenes. The main objective was to investigate new uses for these adsorbent materials which had been previously employed for treatment of aqueous solutions or effluents containing metals such as Co2+ and Cr3+. The adsorption efficiency of Co2+ and Cr3+ on SCB2 and EB was evaluated by adsorption isotherms and other techniques such as XRD, ICP-AES and TGA. Catalytic activity of the four new catalysts, SCB2-Co, SCB2-Cr, EB-Co, and EB-Cr, were assessed in the oxidation reaction of β-citronellol(1), (+)-limonene(2), and (−)-β-pinene(3) in a free solvent system. Results obtained demonstrated that these materials were promising catalysts for the oxidation of monoterpenes. Reactant conversion ranged from 49 to 78% as determined by GC analysis and a combined selectivity up to 59% for the oxidation products was achieved.

We report herein a systematic investigation on the effect of the size of silver (Ag) nanoparticles employed as starting materials over the morphological features and catalytic performances of AgPt nanoshells produced by a combination of galvanic replacement between Ag and PtCl6(2-) and PtCl6(2-) reduction by hydroquinone. More specifically, we focused on Ag nanoparticles of four different sizes as starting materials, and found that the outer diameter, shell thickness, and the number of Pt surface atoms of the produced nanoshells increased with the size of the starting Ag nanoparticles. The produced AgPt nanoshells were supported into SiO2, and the catalytic performances of the AgPt/SiO2 nanocatalysts toward the gas-phase oxidation of benzene, toluene, and o-xylene (BTX oxidation) followed the order: AgPt 163 nm/SiO2AgPt 133 nm/SiO2AgPt 105 nm/SiO2AgPt 95 nm/SiO2. Interestingly, bigger AgPt nanoshell sizes lead to better catalytic performances in contrast to the intuitive prediction that particles having larger outer diameters tend to present poorer catalytic activities due to their lower surface to volume ratios as compared to smaller particles. This is in agreement with the H2 chemisorption results, and can be assigned to the increase in the Pt surface area with size due to the presence of smaller NPs islands at the surface of the nanoshells having larger outer diameters. This result indicates that, in addition to the overall diameters, the optimization of the surface morphology may play an important role over the optimization of catalytic activities in metal-based nanocatalysts, which can be even more pronounced that the size effect. Our data demonstrate that the control over surface morphology play a very important role relative to the effect of size to the optimization of catalytic performances in catalysts based on noble-metal nanostructures.

Nanorattles, comprised of a nanosphere inside a nanoshell, were employed as the next generation of plasmonic catalysts for oxidations promoted by activated O2 . After investigating how the presence of a nanosphere inside a nanoshell affected the electric-field enhancements in the nanorattle relative to a nanoshell and a nanosphere, the SPR-mediated oxidation of p-aminothiophenol (PATP) functionalized at their surface was investigated to benchmark how these different electric-field intensities affected the performances of Au@AgAu nanorattles, AgAu nanoshells and Au nanoparticles having similar sizes. The high performance of the nanorattles enabled the visible-light driven synthesis of azobenzene from aniline under ambient conditions. As the nanorattles allow the formation of electromagnetic hot spots without relying on the uncontrolled aggregation of nanostructures, it enables their application as catalysts in liquid phase under mild conditions using visible light as the main energy input.

We herein report the preparation of AgAu nanotubes displaying controlled surface morphologies and optical properties by varying the reaction temperature during the galvanic reaction between Ag nanowires and AuCl4-(aq). As the AgAu nanotubes presented similar sizes and compositions, they enabled us to isolate the influence of surface morphology and optical properties over their catalytic and plasmonic photocatalytic activities towards methylene blue oxidation. At 25 °C, AgAu nanotubes (AgAu 25) presented branched walls and surface plasmon resonance (SPR) band with low intensities in the visible were obtained. However, at 100 °C, the AgAu nanotubes (AgAu 100) presented smooth surfaces and SPR bands that closely matched the emission spectra of a commercial halogen-tungsten lamp. The AgAu 25 nanotubes displayed better catalytic performances in classical heterogeneous catalysis as a result of its branched walls that lead to increased surface areas relative to the smooth nanotubes. Conversely, AgAu 100 nanotubes showed better activities in plasmonic photocatalysis due to its broader and more intense SPR bands. Thus, our results demonstrate the potential of the control over morphological and optical features towards the optimization of distinct catalytic phenomena.

In order to enable practical applications of SPR-excitation in heterogeneous catalysis, facile procedures for the synthesis of plasmonic catalysts as well as the use of commercially available and inexpensive lamps as the excitation source are highly desirable. In this context, the development of catalysts displaying SPR extinction that matches, as much as possible, the emission spectra of commercially available lamps represent an intuitive strategy to maximize performance. We report the design and facile synthesis of AgAu nanorings displaying SPR extinction that closely matches the emission spectra of a commercial halogen–tungsten lamp. The AgAu nanorings were employed as catalysts for the SPR-mediated oxidation of methylene blue in the liquid phase (water as the solvent), under ambient conditions, and using a halogen–tungsten lamp as the only energy input. The activity of the nanorings was benchmarked against Ag and Au nanospheres. We found that the activity of the nanorings was higher relative to the nanospheres, and that both hot electrons and holes generated as a result of the SPR excitation participated in the methylene blue oxidation reaction with similar relative contributions. Our results show that the rational design of metallic nanostructures plays an important role for enabling practical applications in the field of plasmonic catalysis, in which facile procedures can be employed for the synthesis of the catalysts (attractive for large-scale production) and commercial lamps may be used as the only energy input.

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.

We describe herein an investigation on how the number of Pt surface atoms and nature of exposed surface facets affect the catalytic performances of AgPt nanomaterials displaying controlled surface morphologies (smooth or rough surfaces), shapes (spherical or one-dimensional), and hollow interiors towards CO oxidation. More specifically, we focused on AgPt nanoshells (smooth surfaces), assembled nanoparticles (rough surfaces), nanotubes with smooth surfaces, and nanotubes with rough surfaces. We found that their catalytic performances followed the order: nanotubes with smooth surfaces > nanoshells, nanotubes with rough surfaces > assembled nanoparticles. The better catalytic activity observed for the nanoshells relative to the assembled nanoparticles can be associated with their higher number of Pt surface atoms. Even though the nanotubes with rough surfaces had a higher number of Pt surface atoms relative to the nanotubes with smooth surfaces, the latter displayed higher catalytic activities as a result of the preferential exposure of {100} facets, which are the most active towards CO oxidation relative to {111} and {110}. Interestingly, the nanotubes with smooth surfaces also displayed higher catalytic activities when compared to the nanoshells, showing that the preferential exposure of {100} side facets compensated the decrease in their number of Pt surface atoms relative to the nanoshells. Our data showed that the catalytic performances were strongly dependent on the surface morphologies, in which the preferential exposure of more active surface facets may play a significant role in the optimization of performances relative to the number of Pt surface atoms.

In this paper, Co/CeO 2 catalysts, with different cobalt contents were prepared by the polymeric precursor method and were evaluated for the steam reforming of ethanol. The catalysts were characterized by N 2 physisorption (BET method), X-ray diffraction (XRD), UV–visible diffuse reflectance, temperature programmed reduction analysis (TPR) and field emission scanning electron microscopy (FEG-SEM). It was observed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. Physical–chemical characterizations revealed that the cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. The catalyst with the highest cobalt content showed the best performance among the catalysts tested, exhibiting complete ethanol conversion, hydrogen selectivity close to 66% and good stability at a reaction temperature of 600 °C.

The surface-plasmon-resonance (SPR)-mediated catalytic activities of Ag and Au nanoparticles have emerged a relatively new frontier in catalysis in which visible light can be employed as an eco-friendly energy input to drive chemical reactions. Although this phenomenon has been reported for a variety of transformations, the effect of the nanoparticle shape and crystalline structure on the activities remains unclear. In this paper, we investigated the SPR-mediated catalytic activity of Ag quasi-spheres, cubes, triangular prisms, and wires toward the oxidation of p-aminothiophenol to p,p′-dimercaptoazobenzene by activated O2. The activities at 632.8 nm excitation followed the order triangular prisms and quasi-spheres > wires ≫ cubes. These results indicated that the shape, optical properties, and crystal structure played an important role in the detected SPR-mediated activities.

New AgAu tadpole nanocrystals were synthesized in a one-step reaction involving simultaneous galvanic replacement between Ag nanospheres and AuCl4(-)(aq.) and AuCl4(-)(aq.) reduction to Au in the presence of citrate. The AgAu tadpoles display nodular polycrystalline hollow heads, while their undulating tails are single crystals. The unusual morphology suggests an oriented attachment growth mechanism. Remarkably, a 1 nm thick Ag layer was found to segregate so as to cover the entire surface of the tadpoles. By varying the nature of the seeds (Au NPs), double-headed Au tadpoles could also be obtained. The effect of a number of reaction parameters on product morphology were explored, leading to new insights into the growth mechanisms and surface segregation behavior involved in the synthesis of bimetallic and anisotropic nanomaterials.

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

We describe the synthesis of AgPt hollow nanodendrites employing Ag nanospheres as seeds by combining a galvanic replacement reaction between Ag and PtCl62− and PtCl62− reduction to Pt in the presence of hydroquinone. AgPt hollow nanodendrites comprised of several Pt islands ≈6 nm in diameter could be obtained in only 15 s following the addition of PtCl62− to a suspension containing Ag nanospheres, and their size and composition could be tuned as a function of the growth time. The synthesis could be scaled up by 100 folds, which enabled us to uniformly support the AgPt nanostructures onto commercial silica. The AgPt nanodendrites displayed good catalytic activities for both the 4-nitrophenol reduction and the BTX oxidation reactions. The results presented herein may inspire the synthesis of noble metal nanostructures displaying attractive features for catalysis, such as hollow interiors, ultrathin walls, and uniform dispersion over solid supports (solid supported catalysts).