Search

The intensified use of palladium nanoparticles (PdNPs) in many chemical reactions, jewellery, electronic devices, in car catalytic converters and in biomedical applications lead to a significant increase in palladium exposure. Pd can cause allergic contact dermatitis when in contact with the skin. However, there is still a lack of toxicological data related to nano-structured palladium and information on human cutaneous absorption. In fact, PdNPs, can be absorbed through the skin in higher amounts than bulk Pd because NPs can release more ions. In our study, we evaluated the absorption of PdNPs, with a size of 10.7 ± 2.8 nm, using intact and damaged human skin in Franz cells. 0.60 mg cm −2 of PdNPs were applied on skin surface for 24 h. Pd concentrations in the receiving solutions at the end of experiments were 0.098 ± 0.067 μg cm −2 and 1.06 ± 0.44 μg cm −2 in intact skin and damaged skin, respectively. Pd flux permeation after 24 h was 0.005 ± 0.003 μg cm −2 h −1 and 0.057 ± 0.030 μg cm −2 h −1 and lag time 4.8 ± 1.7 and 4.2 ± 3.6 h, for intact and damaged skin respectively. This study indicates that Pd can penetrate human skin.

Hybridization of metal oxides with nanocarbons has become a very fertile soil of research, given the synergy of the two phases that results in most cases in an improved photo-catalytic performance. Despite the mechanism is still uncertain, it has been established that the presence of a nanocarbon can retard recombination of the photo-excited electrons and holes. The improved activity critically depends on the method of synthesis, which should be designed as to have the maximum C-metal oxide contact. Much research has been conducted on graphene and carbon nanotubes, but other carbon structures are slowly coming to surface. The vast majority of reports focuses on photo-degradation of organic contaminants, but application to energy related fields is becoming more and more popular.

Carbon supported nanostructured palladium or palladium alloys are considered the best performing anode electrocatalysts currently employed in alkaline electrolyte membrane direct ethanol fuel cells (AEM-DEFCs). High initial peak power densities are generally obtained as Pd preferentially favors the selective oxidation of ethanol forming acetate thus avoiding strongly poisoning intermediates such as CO. However, few studies exist that investigate DEFC performance in terms of both energy efficiency and discharge energy density, as well as power density depending on the concentration of fuel. In this paper we have determined such parameters for room temperature air breathing AEM-DEFCs equipped with Pd based anodes, anion exchange membranes and FeCo/C cathode electrocatalysts. Combined with the optimization of the fuel composition a maximum energy efficiency of approximate to 7% was obtained for this AEM-DEFC. Such a performance suggests that devices of this type are suitable for supplying low power applications such as small portable electronic devices.

In questo lavoro di tesi, l’approccio della nano-catalisi è stato impiegato nello sviluppo di nanomateriali catalitici a base di nanoparticelle e nano-cluster dei metalli di transizione. Nanoparticelle di Pt porose e sfaccettate sono state concepite e sintetizzate attraverso l’impiego di tecniche chimiche in fase liquida, atte a risaltare la porosità delle nanoparticelle e, nel contempo, a promuovere l’esposizione di determinati piani cristallini sulla superficie. La peculiare struttura porosa delle nanoparticelle, decorata da piccoli cristalliti sfaccettati, è stata sviluppata a partire dall’evoluzione di piccoli nuclei cristallini. Tale evoluzione durante la sintesi è stata monitorata tramite esperimenti di microscopia elettronica. Esperimenti di controllo sono stati svolti a sostegno della scelta delle condizioni di reazione adottate e a supporto della necessità di un appropriato rapporto OLAM/OLAC per garantire l’effettiva riuscita della sintesi. L’effettivo controllo delle proprietà, ottenute attraverso l’ingegnerizzazione della superficie delle nanoparticelle, è stato corroborato da test catalitici sull’elettro-riduzione dell’ossigeno e l’ossidazione di metanolo, da cui è risultata una performance superiore delle nanoparticelle porose rispetto ad un catalizzatore commerciale ed uno non poroso. (Pd8/Al2O3) è stato preparato e studiato tramite un approccio di progettazione razionale a partire dalla sintesi del complesso Pd8(SCH2COOMe)16. Il complesso di Pd(II), avente una nuclearità altamente definita, può essere fonte di cluster non protetti estremamente attivi dopo il processo di riduzione atto alla rimozione dei leganti organici e dello zolfo. In seguito alla deposizione del complesso, eseguita per irraggiamento di luce UV e con l’uso di basse concentrazioni di Pd in modo da escludere fenomeni di aggregazione, il pre-catalizzatore è stato in seguito ridotto ad alte temperature in idrogeno favorendo la generazione di cluster metallici di palladio. Approfondite caratterizzazioni, lungo tutto il processo di preparazione del catalizzatore, sono state svolte tramite l’utilizzo di tecniche TEM, XPS ed EXAFS, confermando la ridotta dimensione dei cluster e la loro natura metallica. Il catalizzatore nanostrutturato è stato sottoposto a reazioni di cross coupling di Suzuki, con bromuri arilici e acido fenilboronico, mostrando una spiccata attività e selettività. . In aggiunta, il catalizzatore si è dimostrato tollerante verso vari gruppi funzionali durante l’analisi del campo di applicabilità della reazione e molto stabile nei test di riciclo e di disattivazione causato da rilascio di specie metalliche in fase liquida. Infine, cluster di oro ad atomicità precisa sono stati applicati nella preparazione di foto-catalizzatori atti alla produzione di idrogeno da foto-ossidazione di etanolo. Questi cluster di oro a diversa atomicità sono stati impiegati in uno studio di correlazione attività/dimensione. Al livello sub-nanometrico, le proprietà elettroniche dei cluster di oro non hanno una variazione lineare con la dimensione e di conseguenza questo influisce notevolmente sulle performance catalitiche. Ne consegue che studi correlanti l’attività con la dimensione dei cluster sono prioritari in determinare il potere catalitico dei cluster metallici. In questo studio, i cluster Au11, Au18, Au23 and Au25 protetti da leganti tiolati o fosfinici, sono stati preparati ed ancorati su TiO2 utilizzando due diversi approcci basati su irraggiamento con luce UV e impregnazione diretta. I due set di catalizzatori, generati dalle diverse preparazioni, sono stati infine testati per la foto-generazione di idrogeno risultando in superiori attività e stabilità catalitiche rispetto ad un analogo catalizzatore foto-deposto usato come riferimento. In this thesis work, the nano-catalysis philosophy was applied for the development of engineered catalytic nanomaterials based on transition metal nanoparticles (NPs) and nanoclusters (NCs). Porous multifaceted Pt NPs were designed and synthesised via wet-chemical approach meant for the expression of porous features characterized by extended regular planes as surface features. The peculiar porous structure of platinum NPs decorated with faceted crystallites arose from controlled growth of small seeds through progressive evolution that could be monitored by TEM experiments. Control experiments were performed to support the selected reaction conditions as the optimal in delivering the desired features and to corroborate the needful use of a defined surfactant mixture composition for the successful NPs formation. The property control on these NPs, through surface modification, was confirmed by the catalytic tests performed in electrochemical ORR and MOR achieving superior performances compared to a commercial and a non-porous benchmark catalysts. Concerning the control of properties through size engineering, Pd8/Al2O3 catalyst was prepared and studied through a rational design approach, starting from the synthesis of Pd8(SCH2COOMe)16 complex. Unlike the conventional preparation of small metal clusters, in this work the atomicity control was attained by the use of organometallic chemistry. The Pd(II) complex, having a defined nuclearity, can provide highly active unprotected clusters once removal of ligands and reduction of Pd is performed. After complex deposition onto alumina by UV irradiation, working at low Pd concentration in order to preserve the atomicity, the pre-catalyst was reduced at high temperature with hydrogen to deliver metallic Pd clusters. Extensive characterization, through the various steps of catalyst preparation, performed by TEM, XPS and EXAFS, confirmed the small size of the clusters and their metallic nature. The nanostructured catalyst was used in Suzuki coupling reactions of aryl bromides and phenylboronic acid, resulting in very high activity and selectivity. Additionally, the catalyst was able to deliver substituted biphenyls with great tolerance toward the use of various substituted bromobenzenes and demonstrated enhanced stability as evinced by the recycling and leaching tests. Lastly, atomically precise Au NCs were applied in the preparation of photocatalysts to exploit their potential in the production of hydrogen from ethanol. Au NCs with different atomicity were employed in order to study their size influence on the activity. At the sub-nanometric level, the electronic properties of Au NCs have a non-monotonic oscillation that consequently can influence the performance of a catalyst, thus studies on the size/activity relationship are pivotal to provide a deeper understanding of the behaviour of such metal nanoobjects in catalysis. In this study Au11, Au18, Au23 and Au25 thiolate and phosphine protected clusters were synthesised and dispersed on TiO2 by two different approaches based on UV irradiation and in situ impregnation. The two sets of catalysts were tested in the photocatalytic hydrogen production resulting superior in activity and stability toward a photodeposited Au/TiO2 benchmark catalyst.

Recently, the field of dual photocatalysis has grown rapidly, to become one of the most powerful tools for the functionalization of organic molecules under mild conditions. In particular, the merging of Earth-abundant nickel-based catalytic systems with visible-light-activated photoredox catalysts has allowed the development of a number of unique green synthetic approaches. This goes in the direction of ensuring an effective and sustainable chemical production, while safeguarding human health and environment. Importantly, this relatively new branch of catalysis has inspired an interdisciplinary stream of research that spans from inorganic and organic chemistry to materials science, thus establishing itself as one dominant trend in modern organic synthesis. This Review aims at illustrating the milestones on the timeline evolution of the photocatalytic systems used, with a critical analysis toward novel applications based on the use of photoactive two-dimensional carbon-based nanostructures. Lastly, forward-looking opportunities within this intriguing research field are discussed.

In this work, the development of a novel efficient heterogeneous catalytic system capable of driving Knoevenagel condensation reactions between benzaldehydes and malononitrile was reported. Specifically, we explored a post-synthetic modification of graphitic carbon nitride (g-CN) through a strong oxidation treatment by acid mixture (HNO3/H2SO4). The as-prepared oxidized CN material (CNO) shows a large number of surface acidic moieties, that can be easily deprotonated through an aqueous alkaline wash with different bases (NaOH, K2CO3, t-BuOK), to introduce a high density of reactive basic sites. The best catalyst is obtained with NaOH as the base (CNO-NaOH), and displays high reactivity and good tolerance towards functional group variations of the reagents, thus emerging as a potential new recyclable carbon nitride-based structure for organic base catalysis.

Carbon nitride (CN) is a heterogeneous photocatalyst that combines good structural properties and a broad scope. The photocatalytic efficiency of CN is associated with the presence of defective and radical species. An accurate description of defective states—both at a local and extended level—is key to develop a thorough mechanistic understanding of the photophysics of CN. In turn, this will maximise the generation and usage of photogenerated charge carriers and minimise wasteful charge recombination. Here the influence of morphology and light-excitation on the number and chemical nature of radical defects is assessed. By exploiting the magnetic dipole-dipole coupling, the spatial distribution of native radicals in CN is derived with high precision. From the analysis an average distance in the range 1.99–2.34 nm is determined, which corresponds to pairs of radicals located approximately four tri-s-triazine units apart.

Photocatalytic hydrogen production from biomass is a promising alternative to water splitting thanks to the oxidation half-reaction being more facile and its ability to simultaneously produce solar fuels and value-added chemicals. Here, we demonstrate the coproduction of H2 and diesel fuel precursors from lignocellulose-derived methylfurans via acceptorless dehydrogenative C−C coupling, using a Ru-doped ZnIn2S4 catalyst and driven by visible light. With this chemistry, up to 1.04 g gcatalyst−1 h−1 of diesel fuel precursors (~41% of which are precursors of branched-chain alkanes) are produced with selectivity higher than 96%, together with 6.0 mmol gcatalyst−1 h−1 of H2. Subsequent hydrodeoxygenation reactions yield the desired diesel fuels comprising straight- and branched-chain alkanes. We suggest that Ru dopants, substituted in the position of indium ions in the ZnIn2S4 matrix, improve charge separation efficiency, thereby accelerating C−H activation for the coproduction of H2 and diesel fuel precursors. Biomass can be used to scavenge photogenerated holes in photocatalytic hydrogen production, but the oxidized molecules that form are not always useful products. Here, the authors use Ru-ZnIn2S4 to photocatalyse the dehydrogenative C−C coupling of lignocellulose-derived methylfurans, forming both hydrogen and diesel fuel precursors.

A widespread approach to modulate the performances of heterogeneous catalysts is the use of bimetallic nanoparticles (NPs) as the active phase. However, studying the relationship between the NPs structure and catalytic properties requires well-defined systems, having uniform composition, size and nanostructure, which cannot be achieved by traditional methods (e.g. impregnation). Here, we developed wet-chemistry synthetic routes to prepare Pd Pt NPs or Pt-core@Pd-shell NPs of small size and well-controlled composition and structure, protected by mercaptoundecanoic acid (MUA) moieties. The pristine NPs were tested for H2 production by NH3BH3 hydrolysis, in order to systematically investigate the effect of composition and of synthetic route on the activity of the systems. Depending on the preparation method, two distinct trends of activity were observed, rationalized in terms of the extent of surface functionalization by MUA. The MUA protective layer was found to effectively stabilize the NPs dispersion while maintaining high activity in certain cases (Pt-rich NPs), and was demonstrated to be essential for catalyst recycling. In order to further study structure-activity relationships of Pd Pt NPs after ligand removal, nanostructured Pd Pt@CeO2-based catalysts were prepared by self-assembly route. Regardless of the starting NPs structure (alloy or core-shell), similar water gas shift reaction performances were observed, due to the structural rearrangements occurring upon oxidation and reduction thermal treatments, which led to the formation of Pt-rich core@Pd Pt-shell under reducing conditions.

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

Photocatalysis is one potential solution to the energy and environmental crisis and greatly relies on the development of the catalysts. Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, is eco‐friendly and exhibits strong oxidation ability, and has attracted considerable attention from researchers. Furthermore, unique Lewis acid sites (LASs) and Brønsted acid sites (BASs) are observed on Nb2O5 prepared by different methods. Herein, the recent advances in the synthesis and application of Nb2O5‐based photocatalysts, including the pure Nb2O5, doped Nb2O5, metal species supported on Nb2O5, and other composited Nb2O5 catalysts, are summarized. An overview is provided for the role of size and crystalline phase, unsaturated Nb sites and oxygen vacancies, LASs and BASs, dopants and surface metal species, and heterojunction structure on the Nb2O5‐based catalysts in photocatalysis. Finally, the challenges are also presented, which are possibly overcome by integrating the synthetic methodology, developing novel photoelectric characterization techniques, and a profound understanding of the local structure of Nb2O5.

Although the low-temperature reaction mechanism of catalytic CO oxidation reaction remains unclear, the active sites of copper play a crucial role in this mechanism. One-step aerosol-assisted self-assembly (AASA) process has been developed for the synthesis of mesoporous Cu-doped TiO2 microspheres (CuTMS) to incorporate copper into the TiO2 lattice. This strategy highly enhanced the dispersion of copper from 41.10 to 83.65%. Long-term stability of the as-synthesized CuTMS materials for catalytic CO oxidation reaction was monitored using real-time mass spectrum. Isolated CuO and Cu-O-Ti were formed as determined by X-ray photoelectron spectroscopy (XPS). The formation of the Cu-O-Ti bonds in the crystal lattice changes the electron densities of Ti(IV) and O, causing a subsequent change in Ti(III)/Ti(IV) and Onon/OTotal ratio. 20CuTMS contained the highest lattice distortion (0.44) in which the Onon/OTotal ratio is lowest (0.18). This finding may be attributed to the absolute formation of the Cu-O-Ti bonds in the crystal lattice. However, the decrease of Ti(III)/Ti(IV) ratio to about 0.35 of 25CuTMS was caused by the CuO cluster formation on the surface. N2O titration-assisted H2 temperature-programmed reduction and in-situ Fourier transform infrared spectroscopy revealed the properties of copper and effects of active sites.

Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.

Practical-scale on-site production of hydrogen peroxide (H2O2) via two-electron (2e(-)) oxygen reduction reaction (ORR) relies on efficient, robust, and selective electrocatalysts. Among them, carbon-based materials are cheap, abundant, durable, and their surface properties can be tuned to favor the 2e(-) ORR pathways, resulting in higher efficiency and facilitating possible scale-up towards commercially appealing levels. Here, we demonstrate that the selective installment of carboxyl groups on the surface of N-doped graphene yielding a material named graphene acid (N-GA) promotes the catalytic 2e(-) ORR, achieving a H2O2 faradaic efficiency (FE) as high as 70 % in acidic media (pH=0.96) and a H2O2 productivity in long term bulk electrolysis that could reach 107.8 mmol g(catalyst)(-1) h(-1) under optimized conditions. Extended XPS analysis and density functional theory (DFT) calculations revealed that surface carboxylic acid functional groups play a significant role in achieving the high activity of N-GA for 2e(-) ORR.

A heterogeneous catalyst is a backbone of modern sustainable green industries; and understanding the relationship between its structure and properties is the key for its advancement. Recently, many upscaling synthesis strategies for the development of a variety of respectable control atomically precise heterogeneous catalysts are reported and explored for various important applications in catalysis for energy and environmental remediation. Precise atomic-scale control of catalysts has allowed to significantly increase activity, selectivity, and in some cases stability. This approach has proved to be relevant in various energy and environmental related technologies such as fuel cell, chemical reactors for organic synthesis, and environmental remediation. Therefore, this review aims to critically analyze the recent progress on single-atom catalysts (SACs) application in oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and chemical and/or electrochemical organic transformations. Finally, opportunities that may open up in the future are summarized, along with suggesting new applications for possible exploitation of SACs.

The concept of self-regenerating or "smart" catalysts, developed to mitigate the problem of supported metal particle coarsening in high-temperature applications, involves redispersing large metal particles by incorporating them into a perovskite-structured support under oxidizing conditions and then exsolving them as small metal particles under reducing conditions. Unfortunately, the redispersion process does not appear to work in practice because the surface areas of the perovskite supports are too low and the diffusion lengths for the metal ions within the bulk perovskite too short. Here, we demonstrate reversible activation upon redox cycling for CH4oxidation and CO oxidation on Pd supported on high-surface-area LaFeO3prepared as a thin conformal coating on a porous MgAl2O4support using Atomic Layer Deposition (ALD). The LaFeO3film, less than 1.5-nm thick, was shown to be initially stable to at least 900 °C. The activated catalysts exhibit stable catalytic performance for methane oxidation after high-temperature treatment.

Photocatalytic hydrogen (H2) production is a process that converts solar energy into chemical energy by means of a suitable photocatalyst. After the huge amount of systems that have been tested in the last forty years, the advent of nanotechnology and a careful design at molecular level, allow to obtain attractive activity, even using pure visible light. At the same time we are approaching reasonable photocatalyst stability in laboratory test, and the attention is paid to identify cost-effective photocatalysts that might find real applications. This Review provides a broad overview of the elementary steps of the heterogeneous photocatalytic H2 production, including an outline of the physico-chemical reactions occurring on semiconductors and cocatalysts. The use of different renewable oxygenates as sustainable sacrificial agent for the H2 production is outlined, in view of a transition from fossil fuels to pure water splitting. Finally, the recent advances in the development of photocatalyst are discussed focusing on the current progress in organic and hybrid organic/inorganic photocatalysts.

The importance of sensing hydrogen peroxide (H2O2) is due to its ubiquity, being extensively used in industry and also being a biologically relevant side-product of several enzymatic processes. Electrochemical sensing is one of the most robust and simple methods for sensing H2O2 and the discovery of new electroactive materials, particularly at the nanoscale, represents a very hot topic of research. Here, we prove that upon appropriate integration of oxidized single-walled carbon nanohorns (ox-SWCNHs) into a per se moderate H2O2 sensor such as cerium dioxide (CeO2), the sensitivity toward H2O2 is enhanced by almost two orders of magnitude (from 0.4 to 160 μA cm−2 mM−1), on par with that of state-of-the-art metal or metal oxide-based sensors. The modified electrode is also very stable (82% response after 2 weeks of continuous use) and the results highly reproducible. The developed nanohybrid ox-SWCNHs@CeO2, characterized fully and whose average size is about 70 nm as measured by both TEM and AFM, was also tested in real case studies such as washing liquids and milk and was confirmed to be a robust and highly selective material, being not affected neither by the presence of complex matrices, nor by interferents in several organic substrates. The high recovery confirmed the excellent specificity and flexibility of this new electrocatalytic material. Fil: Bracamonte, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. University of Trieste; Italia Fil: Melchionna, Michele. University of Trieste; Italia Fil: Giuliani, Angela. University of Trieste; Italia Fil: Nasi, Lucía. CNR-IMEM Institute; Italia Fil: Tavagnacco, Claudio. University of Trieste; Italia Fil: Prato, Maurizio. University of Trieste; Italia. Carbon Nanobiotechnology Laboratory; España. BasqueFdnSci; España Fil: Fornasiero, Paolo. University of Trieste; Italia

Modification of a 1 wt% Pd/CeO2 catalyst by Atomic Layer Deposition of thin ZrO2 films was studied. Calcination of the unmodified Pd/CeO2, prepared by precipitation of aqueous Ce(NO3)3 solutions, with Pd added by impregnation, caused a large decrease in surface area and an increase in crystallite size between 673 K and 1073 K; however, catalysts modified by 0.4 nm ZrO2 films showed no change in either surface area or CeO2 crystallite size upon calcination to 1073 K. Methane-oxidation rates in 0.5% CH4 and 5% O2 were slightly lower on the ZrO2-covered catalyst when both materials were calcined at 673 K but the activity of the ZrO2-modified catalyst did not decrease with catalyst calcination temperature. Both catalysts showed good activity for the water-gas-shift reaction but the ZrO2 film improved sulfur tolerance by preventing formation of cerium sulfates. This paper was also made possible by an NPRP Grant # 6-290-1-059 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. The authors would also like to thank M. Aulick�, T. Ducho? and K. Veltrusk� from Charles University in Prague for the XPS analysis. Scopus

The influence of phosphorus and water on methane catalytic combustion was studied over Pd@CeO2 model catalysts supported on graphite, designed to be suitable for X-ray Photoelectron Spectroscopy/Synchrotron Radiation Photoelectron Spectroscopy (XPS/SRPES) analysis. In the absence of P, the catalyst was active for the methane oxidation reaction, although introduction of 15% H2O to the reaction mixture did cause reversible deactivation. In the presence of P, both thermal and chemical aging treatments resulted in partial loss of activity due to morphological transformation of the catalyst, as revealed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis. At 600 degrees C the combined presence of PO43- and water vapor caused a rapid, irreversible deactivation of the catalyst. XPS/SRPES analysis, combined with operando X-ray Absorption Near Edge Structure (XANES) and AFM measurements, indicated that water induces severe aggregation of CeO2 nanoparticles, exposure of CePO4 on the outer layer of the aggregates and incorporation of the catalytic-active Pd nanoparticles into the bulk. This demonstrates a temperature-activated process for P-poisoning of oxidation catalysts in which water vapor plays a crucial role. (C) 2015 Elsevier B.V. All rights reserved.

One of the recent trends in electrocatalytic reactions involves the oxygen reduction reaction (ORR), where a new paradigm has been shaped to exploit this reaction for the synthesis of hydrogen peroxide (H2 O2 ). H2 O2 is a very versatile chemical of high commercial value, prepared currently through poorly sustainable processes. The emergence of metal-free carbon catalysts for the selective synthesis of H2 O2 is expected to revolutionize ORR research, beckoning at the development of new industrial schemes. The complexities of the mechanism and the factors dominating the selectivity of the process have been unveiled through a combination of theoretical and experimental studies.

The development of efficient homogeneous catalysts for the synthesis of functionalized polyolefins is a challenging topic. Palladium(II) complexes with ?-diimine ligands having a phenanthrene skeleton and 2,6-disubstituted aryl rings (Ar-BIP) were synthesized, characterized, and tested as precatalysts in the copolymerization of ethylene with methyl acrylate. The direct comparison with analogous complexes having the corresponding ?-diimines with an acenaphthene skeleton (Ar-BIAN) was performed. X-ray characterization in the solid state and NMR analysis in solution of both neutral [Pd(Ar-BIP)(CH3)Cl] and monocationic [Pd(Ar-BIP)(CH3)(NCCH3)][PF6] complexes indicate that the Ar-BIP ligands have a higher Lewis basicity and are more strongly coordinated to the metal center in comparison to the Ar-BIAN counterparts. Therefore, the Pd(Ar-BIP) cationic complexes can be regarded as electron-rich metal cations. In addition, they create a higher steric congestion around palladium in comparison to Ar-BIAN, regardless of the substituents on the aryl rings. The monocationic species generate active catalysts for the ethylene/methyl acrylate copolymerization leading to copolymers with Mn values up to 37000 and a content of polar monomer of 5.3 mol %. A detailed study of the catalytic behavior points out that Pd(Ar-BIP) catalysts show a good affinity for the polar monomer, have a good thermal stability, and favor the cleavage of the catalyst resting state, leading to copolymers with Mw values higher than those of the macromolecules produced with the corresponding Pd(Ar-BIAN) under the same reaction conditions. NMR characterization of the produced copolymers points out that the polar monomer is inserted both at the end of the branches and into the main chain, with an enchainment more selective than that achieved when the copolymerization is carried out in dichloromethane. In situ NMR investigations allowed us to detect relevant intermediates of the catalytic cycle and shed light on the nature of possible deactivated species.

The mechanism of formation of Pt@SiO2 as a model of core-shell nanoparticles via water-in-oil reverse microemulsions was studied in detail. By controlling the time of growth of Pt precursors, Pt(OH)(x), after hydrolysis in NH3 aq. before adding SiO2 precursor (TEOS), Pt nanoparticles with a narrow size distribution were produced, from ultrafine metal nanoparticles (

Hybrid organic/inorganic nanocomposites comprised of nanocrystalline iron oxide at the metastable beta-phase and graphitic carbon nitride (g-C3N4) were prepared via a facile in-situ growth strategy embedded in a solid state process. The hybridized beta-Fe2O3/g-C3N4 nanomaterials were thoroughly characterized by a variety of techniques, including UV-vis absorption, nitrogen physisorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). Their photocatalytic activity was evaluated under both simulated solar light and pure visible light irradiation against the photodegradation of methyl orange (MO), rhodamine B (RhB) and phenol. The prepared beta-Fe2O3/g-C3N4 nanocomposites were proven durable and significantly more efficient than the single components. The beta-Fe2O3 content in the final material was tuned to optimize the photocatalytic performance, with particular attention to the activity under visible light. The enhanced photoactivity was attributed to a) the improved optical properties of the prepared nanocomposites, presenting narrower band-gap energies and increased visible light absorption efficiency, and b) to the efficient separation of the photoinduced charge carriers driven by the matched band edges in the heterostructure. The predominant active species responsible for the photodegradation activity were determined and a possible mechanism is proposed. (C) 2016 Elsevier B.V. All rights reserved.

The successful production of a nanostructured and highly dispersed Pd-TiO2 photo-catalyst, using [Pd(Me(2)dazdt)(2)](I-3)(2) (Me(2)dazdt = N,N'-dimethyl-perhydrodiazepine-2,3-dithione) salt, obtained through the selective and safe recovery of palladium from model exhaust three-way catalysts (TWCs), is reported here. The photo-catalyst prepared by the impregnation/photo-reduction of palladium on the support showed improved performance in H-2 production from methanol and in glycerol photo-reforming compared to reference photo-catalysts obtained from conventional Pd-salts. The reported results represent a case of successful palladium "recovery and re-employment" and thus constitute an example of green chemistry by providing, in one route, the environmentally friendly recovery of a critical metal and its employment in the renewable energy field.

The interface of metal-oxide plays pivotal roles in catalytic reactions, but its catalytic function is still not clear. In this study, we report the high activity of nanostructured Ru/ceria (Ru-clusters/ceria) in the ethylene methoxycarbonylation (EMC) reaction in the absence of acid promoter. The catalyst offers 92% yield of MP with TOF of 8666 h–1, which is about 2.5 times of homogeneous Pd catalyst (∼3500 h–1). The interfacial Lewis acid–base pair [Ru-O-Ce-Vo], which consists of acidic Ce-Vo (oxygen vacancy) site and basic interfacial oxygen of Ru-O-Ce linkage, acts as active site for the dissociation of methanol and the subsequent transfer of hydrogen to the activated ethylene, which is the key step in acid-promoter-free EMC reaction. The combination of 1H MAS NMR, pyridine-IR and DFT calculations reveals the hydrogen species derived from methanol contains Bronsted acidity. The EMC reaction mechanism under acid-promoter-free condition over Ru-clusters/ceria catalyst is discussed.

Summary Electrochemical oxygen reduction (ORR) is a challenging approach for the sustainable production of hydrogen peroxide (H 2 O 2 ) and is also a reaction of relevance in fuel-cell applications. Here, we propose an outstanding metal-free electrocatalyst for the unexpectedly selective ORR to H 2 O 2 , consisting of graphitized N-doped single-wall carbon nanohorns (CNHs). The catalyst can operate at acidic pH to a faradic efficiency as high as 98%, but it also shows excellent performance at either physiological or alkaline pH. Moreover, the very positive onset potentials observed at all pH values investigated (+0.40 V, +0.53 V, and +0.71 V at pH 1.0, 7.4, and 13.0, respectively), good stability, and excellent reproducibility make this material a benchmark catalyst for ORR to H 2 O 2 . The outstanding activity arises from a combination of several factors, such as CNH-dependent facilitation of electron delivery, suitable porosity, and a favorable distribution of the types of N atoms.

Mechanically robust, chemically stable and electronically active carbon nanotubes (CNTs) are widely used as supports in catalysis. Synergistic effects between CNT and the active phase critically depend on the homogeneity of the carbon/inorganic interface, whose assembly is difficult to achieve without admixtures of free-standing inorganic matrix. Here we show that Fe-filled CNTs, employed as nanocatalyst supports, allow a facile preparation of highly pure and uniform CNT/nanocatalyst materials, by taking advantage of magnetic separation from poorly-defined components (e.g. aggregates of inorganic nanocatalysts). The higher homogeneity translates into higher catalytic activity in two industrially important processes: the photocatalytic hydrogen production and the water-gas shift reaction, WGSR (increase of ~48% activity for the former and up to ~45% for the latter as compared to catalysts isolated by standard filtration). In addition, the magnetic Fe core in the nanotubes enables effective separation and re-use of the nanocatalyst without loss of activity. This study demonstrates significant potential of magnetic CNTs as next generation of sustainable catalyst supports that can improve production of hydrogen and reduce the use of precious metals.

Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given.

In this manuscript we present a new anode catalyst, a Pd-CeO 2 /C hybrid nanostructured material composed of nanostructured Pd and nanostructured CeO 2 supported on C for direct polyalcohol fuel cells. This material fully characterized by HR-TEM, XRD, Raman spectroscopy, TGA and surface area determination techniques (BET and Chemisorption) is studied for the electrooxidation of ethylene glycol and 1,2-propanediol in electrochemical half cells and complete AEM-FCs. At a cell temperature of 60 °C peak power densities of around 50 mW cm −2 are obtained compared to 20–25 mW cm −2 for an equivalent Pd/C catalyst. For the first time the energy efficiency of such fuel cells has been determined with a value of 2% obtained for the cell fed with 1,2-propandiol. All oxidation products for each fuel have been identified and quantified using HPLC and NMR spectroscopy. From ethylene glycol 80% of glycolate is formed while from 1,2-propandiol 58% of lactate is formed. Both of these compounds are key industrial chemicals.

Catalysts are making our world more sustainable day by day. But how sustainable are catalysts themselves? In this contribution we will give a perspective overview of the progress in dematerializing catalysts, i.e., in using less (critical) materials to deliver the same (or better) level of functionality. This may be accomplished in many ways: improving the catalyst performance and durability by gaining insights in reaction, activation, and deactivation mechanisms; lowering the amount of critical or harmful catalytic components, e.g., by finding cheaper, more abundant, and sustainable substitutes; and making catalysts production and disposal processes more sustainable, e.g., by recycling. Material science and nanotechnology are two essential actors in this process, providing the tools to understand and optimize catalytic materials and processes, and to assess the environmental and toxicological impact of nanomaterials.

In view of the sustainable H2 production, development of more efficient catalysts for photocatalytic reforming of oxygenated compounds is required. In this study, we report the preparation of TiO2 nanocomposite with anatase/brookite composition prepared by hydrothermal treatments of Na-titanate precursor. The anatase/brookite ratio can be modulated changing the synthetic parameters, i.e. precursor/water mass-to volume ratio and hydrothermal treatment duration. The obtained materials present well crystallized particles with polyhedral morphology. The anatase/brookite ratio in the nanocomposite affects the mean size of Pt nanoparticles grown by photodeposition and the photocatalytic activity in H2 production by photodehydrogenation of ethanol, with multiphasic materials presenting smaller Pt nanoparticles and higher H2 production. The present anatase/brookite nanocomposites show higher H2 production normalized to the surface area with respect a reference TiO2 prepared by conventional sol–gel synthesis, suggesting that the present materials might expose a higher fraction of highly reactive facets instead of the most thermodynamically stable.

Carbon nanotubes have emerged as unique carbon allotropes that bear very interesting prospects in catalysis. Their use is mostly related to that of supports for inorganic metal catalysts, including molecular catalysts, metal nanoparticles, metal oxides or even more complex hierarchical hybrids. However, several reports have shown that they can intriguingly act as metal-free catalysts, with performance often superior to that of other carbon materials, in particular when ad hoc organic functional groups are attached prior to catalytic screening. The range of catalytic reactions is quite wide, and it includes standard organic synthesis, electrocatalysis, photocatalysis as well as other important industrial processes. In the last few years, the energy sector has acquired a dominant role as one of the most sought-after fields of application, given its ever-increasing importance in society.

The world is facing an era of global environmental pollution, as a result of the tremendous population growth and the consequent massive fossil fuel-based energy consumption. A significant exploitation of renewable energies is needed to guarantee quality of human life and allow further sustainable growth, but this may take decades to happen. In order to mitigate the negative effect of human activities on the environment in the short- and mid-term, the development of more efficient technologies for emissions abatement and for renewable fuels production is imperative. Heterogeneous catalysis and photocatalysis are two key pillars of a multi-approach strategy to solve these issues. During the last century, catalysts were explored by changing the formulation of multi-component systems in order to find the best performing material for a certain reaction. Since the late 90's, a new approach to catalytic systems improvement emerged: nano-catalysis. Exploiting the tools of nanotechnology, tailored nanostructured materials can now be produced, which show different properties in comparison to their bulky counterparts, often resulting in better catalytic performances. Furthermore, combining the elements of the periodic table in nano-alloys allows to expand the possibility of catalyst generation. Consistently with these approaches, the main focus of this thesis is the synthesis and characterization of well-defined nanostructured and hierarchical materials for environmental and energy-related applications, such as emissions control, biofuels synthesis and photocatalytic H2 production. We show that structural control at the nanoscale is a great instrument for understanding reaction pathways, for studying the nature of catalytic active sites, and for synthesizing more selective, active and stable catalysts. Two synthetic strategies were followed to acquire nanostructural control: a self-assembly method was employed to prepare hierarchical materials starting from functional nanoparticles, and advanced solvothermal methods were used to prepare monodisperse nanocrystals having controlled size and composition. State-of-the-art hierarchical Pd-based catalysts embedded by metal oxide promoters were tested for methane catalytic oxidation in the presence of poisoning compounds typically found in real applications. Detailed surface studies allowed to propose deactivation mechanisms and strategies to improve catalysts resistance to deactivation. Well-controlled nanostructured Pt-based alloys and Ni-Cu alloys showed improved activity, stability and selectivity for hydrodeoxygenation reactions of biomass-derived feedstocks to produce biofuels. The control of nanostructure was pivotal to understand the reason for such enhanced performances. Finally, dye-sensitized photocatalysts were investigated in H2 photocatalytic production under visible light, and state-of-the-art stability and activities were demonstrated. All these findings greatly contributed to the development of catalytic materials for energy-related applications.

Sustainable energy and environmental schemes are one of the central priorities for our society, triggering a massive capital investment on research to define new trajectories for bypassing fossil fuel dependence and move to clean energy and consequent pollution abatement. The last decade has witnessed the rise and establishment of nanomaterials as front runners for a real societal impact of key processes under investigation, such as sustainable hydrogen production and CO2 conversion to fuels. The enormous progresses have been made possible by the opportunity to better understand materials at the nanoscale through the use of more powerful characterization techniques and advanced synthetic strategies. The lesson learned is that appropriately engineered multicomponent nanomaterials may hold the key to the routine industrial establishment of new greener concepts of energy production, with strong repercussions to the quality of life.

Photocatalytic reactions could enhance the share of chemicals produced through renewable sources. The efficiency of photocatalysts drastically depends on light absorption, on the surface energy of the crystals, and on the properties of the nanobuilding blocks assembled in devices. Here, we show that photoelectrochemical water oxidation on brookite TiO2 nanorods is greatly enhanced by engineering the location of Au nanoparticles deposition. Brookite photoanodes show a very low onset potential for water oxidation to H2O2 of -0.2 VRHE due to energetics of exposed crystal facets. By combining electrochemical measurements and ultrafast optical spectroscopy, we link the water oxidation activity with electron-hole recombination phenomena. The preferential Au decoration at the electrode/water interface produces highly enhanced photocurrent, while when Au is distributed along the whole film thickness, the activity is depressed with respect to pure brookite. In the latter case, Au nanoparticles act as recombination centers with plasmonic carriers recombining on the same time scale of their generation (fs). Conversely, Au surface decoration enables a hot electrons lifetime 4 orders of magnitude longer (ns) due to efficient hopping on brookite lateral facets, thus providing an efficient path for plasmon-enhanced solar water oxidation. (Graph Presented).

Palladium(II) complexes with a nonsymmetric bis(aryl-imino)diazabutadiene ligand (ArDAB) have been synthesized and characterized. The new ligand is featured by one aryl ring substituted in ortho positions with methyl groups and the other ring bearing a trifluoromethyl group on the meta positions, leading to a subtle steric and electronic difference on the two nitrogen-donor atoms. This peculiar substitution makes the direct synthesis of the ligand not feasible, and the relevant Pd(II) complex, [Pd(CH3)Cl(ArDAB)], is directly obtained through a template reaction. The corresponding cationic complexes with either acetonitrile or dimethyl sulfoxide have been synthesized and characterized. The X-ray crystal structure of a palladium complex with an alfa-diimine and dimethyl sulfoxide is reported. The monocationic complexes have been tested as precatalysts in the ethylene/methyl acrylate cooligomerization under mild reaction conditions of temperature and pressure. The comparison with the catalytic behavior of the precatalysts with the corresponding nonsymmetric ArBIAN ligand indicated that the active species with the currently investigated ligand is more productive, leading to the formation of ethylene oligomers and ethylene/methyl acrylate cooligomers.

Pd dissolution capabilities of a variety of organic triiodides (OrgI3) in organic solvent, where Org+ = 3,5-bis(phenylamino)-1,2-dithiolylium [(PhHN)2DTL+], 3,5-bis(morpholino)-1,2-dithiolylium (Mo2DTL+); tetrabuthylammonium (TBA+); and tetraphenylphosphonium (Ph4P+), toward the crude metal and model-spent three-way catalyst (TWC), are described here. Enhanced Pd-leaching yields from TWC were obtained using OrgI3 solutions (up to 98%) in spite of the fully inorganic KI3 one (38%) in the same mild conditions. The reaction products were isolated and characterized as Org2[Pd2I6]. Crystallographic and DFT studies highlighted the presence of several ion-pair secondary interactions in the products, which can explain the improved effectiveness of the Pd etching by OrgI3. For comparison purposes, the gold leaching by using R2DTLI3 and the obtained Au complexes were investigated. Preliminary results addressed to recover the metal and the reagents from the etching product showed that (PhHN)2DTLI3 is the most promising reagent to improve sustainability in the whole process.

High-surface-area iron oxides were prepared by Atomic Layer Deposition (ALD) on 130-m(2)/g gamma-Al2O3 for use as a catalyst support. Measurements of the sample mass, surface area, and pore-size distribution as a function of the number of ferrocene-O-2 ALD cycles at 623 K suggested that the iron oxide grew as a dense, conformal film with a growth rate similar to 0.016-nm per cycle. While films with 20 ALD cycles (20Fe(2)O(3)Al(2)O(3), 0.25 g Fe2O3/g Al2O3) were difficult to distinguish by HAADF STEM, EDS mapping indicated the Al2O3 was uniformly coated. Raman Spectroscopy showed the films were in the form of Fe2O3; but XRD measurements on samples with as many as 100 ALD cycles (100Fe(2)O(3)-Al2O3, 0.84g Fe2O3/g Al2O3) showed no evidence for crystalline iron-oxide phases, even after calcination at 1073 K. Specific rates for the water-gas-shift (WGS) reaction on the ALD-coated samples were significantly lower than those on bulk Fe2O3. However, addition of 1 wt.% Pd to Fe2O3/Al2O3 supports prepared by ALD exhibited specific rates that were much higher than that observed when I wt.% Pd was added to Fe2O3/Al2O3 prepared by conventional impregnation of Fe salts, suggesting more uniform contact between the Pd and FeOx phases on samples prepared by ALD.

SO2 poisoning of methane oxidation over alumina-supported, Pd@CexZr1−xO2 nanoparticle catalysts was systematically studied by means of advanced PhotoElectron Spectroscopy (PES) methods. The Pd@CexZr1−xO2 units were synthesized and deposited on two modified-alumina supports, i.e. high surface area modified alumina and a model alumina prepared by Atomic Layer Deposition (ALD) of alumina on Indium Tin Oxide (ITO)/quartz slides. The model support was designed to be suitable for PES analysis and was stable to high temperature treatments (850 °C). Characterization of the high-surface-area (HSA) catalysts by X-Ray Diffraction (XRD), N2 physisorption, CO chemisorption and Transmission Electron Microscopy (TEM) indicated formation of CeO2–ZrO2 (CZ) mixed-oxide crystallites that stabilize the Pd active phase against sintering. Correlation of methane-oxidation rates with PES results demonstrated two distinct mechanisms for deactivation by SO2. Below 450 °C, the presence of SO2 in the feed led to partial reduction of the active PdO phase and to the formation of sulfates on the Pd. Above 500 °C, poisoning by SO2 was less severe due to spillover of the sulfates onto the oxide promoter. Pd@ZrO2 catalysts showed the best resistance to SO2 poisoning, outperforming analogous Pd@CZ mixed-oxide catalysts, because there was less sulfate formation and the sulfates that did form could be removed during regeneration. The authors acknowledge CERIC-ERIC for open access to instrumentation and user support. This paper was also made possible by a NPRP Grant #6-290-1-059 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. Scopus

Advances in the synthesis of pure brookite and brookite-based TiO2 materials have opened the way to fundamental and applicative studies of the once least known TiO2 polymorph. Brookite is now recognized as an active phase, in some cases showing enhanced performance with respect to anatase, rutile or their mixture. The peculiar structure of brookite determines its distinct electronic properties, such as band gap, charge–carrier lifetime and mobility, trapping sites, surface energetics, surface atom arrangements and adsorption sites. Understanding the relationship between these properties and the photocatalytic performances of brookite compared to other TiO2 polymorphs is still a formidable challenge, because of the interplay of many factors contributing to the observed efficiency of a given photocatalyst. Here, the most recent advances in brookite TiO2 material synthesis and applications are summarized, focusing on structure/activity relation studies of phase and morphology-controlled materials. Many questions remain unanswered regarding brookite, but one answer is clear: Is it still worth studying such a hard-to-synthesize, elusive TiO2 polymorph? Yes.