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Electronic waste as an alternative source of palladium is used for the preparation of heterogeneous catalysts for methane oxidation. The strategy developed in this paper involves two steps: optimization of the leaching protocol to recover the Pd from the waste, and development of a suitable impregnation protocol directly from the leachate, which is a strongly acidic solution. The precipitation‐deposition technique is particularly suitable for the preparation of catalysts from acidic media. The impact of Ba, Bi, and Ag impurities on the catalytic performance is studied on model catalysts. The presence of these elements and their impact on the catalytic properties are analyzed and discussed using X‐ray diffraction, nitrogen physisorption, scanning and transmission electron microscopy. Through variation of the pH, the impurities co‐deposited with Pd can be limited and the catalytic performance of catalysts derived from real waste can be greatly enhanced. [ABSTRACT FROM AUTHOR]

Low-temperature solution phase synthesis of nanomaterials using designed molecular precursors enjoys tremendous advantages over traditional high-temperature solid-state synthesis. These include atomic-level control over stoichiometry, homogeneous elemental dispersion and uniformly distributed nanoparticles. For exploiting these advantages, however, rationally designed molecular complexes having certain properties are usually required. We report here the synthesis and complete characterization of new molecular precursors containing direct Sn–E bonds (E = S or Se), which undergo facile decomposition under different conditions (solid/solution phase, thermal/microwave heating, single/mixed solvents, varying temperatures, etc.) to afford phase-pure or mixed-phase tin chalcogenide nanoflakes with defined ratios. [ABSTRACT FROM AUTHOR]

Rational design and precise engineering are needed to optimize the structural and chemical parameters of functional materials. In this work, we demonstrate how pre-formed binary metal selenides can be an excellent synthetic choice for the synthesis of ternary coinage metal selenide nanoparticles (NPs) with controlled composition. The mild conditions required to obtain these ternary coinage metal selenide NPs offered an easy synthesis of n% CuAgSe–TiO2 (n = 0.01, 0.1, 0.3 and 1.0 mol%) nanocomposites for photocatalytic applications without compromising the structural and morphological characteristics of TiO2 and without having any organic ligands around the NPs. The use of ternary metal selenide nanocomposites CuAgSe–TiO2 results in a clear improvement in their photocatalytic activity for the photodegradation of formic acid as compared to the well-known benchmark for photocatalysis, TiO2 (P25), and its binary metal selenide nanocomposites Cu2−xSe–TiO2. DFT calculations establish semi-metallic behavior of CuAgSe NPs and show that CuAgSe–TiO2 forms a semimetallic-semiconductor heterojunction allowing a better charge separation to enhance its photocatalytic activity. [ABSTRACT FROM AUTHOR]

Site poisoning is a powerful method to unravel the nature of active sites or reaction intermediates. The nature of the intermediates involved in the hydrogenation of CO was unraveled by poisoning alumina-supported cobalt catalysts with various concentrations of tin. The rate of formation of the main reaction products (methane and propylene) was found to be proportional to the concentration of multi-bonded CO, likely located in hollow sites. The specific rate of decomposition of these species was sufficient to account for the formation of the main products. These hollow-CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions used here, while linear CO are mostly spectators. [ABSTRACT FROM AUTHOR]

Site poisoning is a powerful method to unravel the nature of active sites or reaction intermediates. The nature of the intermediates involved in the hydrogenation of CO was unraveled by poisoning alumina-supported cobalt catalysts with various concentrations of tin. The rate of formation of the main reaction products (methane and propylene) was found to be proportional to the concentration of multi-bonded CO, likely located in hollow sites. The specific rate of decomposition of these species was sufficient to account for the formation of the main products. These hollow-CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions used here, while linear CO are mostly spectators. [ABSTRACT FROM AUTHOR]

Abstract: Standard chemical and physical methods to control the size of supported metallic nanoparticles are generally not compatible with the harsh conditions of applications (high temperature, presence of steam). Sintering of nanoparticles usually occurs, leading to particle growth and eventually to a degradation of physical properties. Here we describe a generic process for synthesizing nanoalloys of controlled size (2–10 nm) and composition encapsulated in zeolite nanoboxes. The originality of the synthesis design is that the nanoboxes act both as nanoreactors in which the bimetallic particles are formed and as protective ultra‐microporous shells, which prevent sintering by coalescence even under harsh conditions. Moreover, the present process allows for control over the size and composition of the NPs, which are factors that ultimately determine the catalytic properties. A series of mono‐ (Au, Pd, Pt) or bi‐ (AuAg, PdAg, PtAg and PdPt) metallic nanoparticles individually encapsulated in hollow silicalite‐1 single crystals have been prepared and characterized. The simultaneous presence of Ag and Au at the surface of Au161Ag22 NPs has been demonstrated by results of the catalytic activity for CO oxidation near room temperature. [ABSTRACT FROM AUTHOR]

Mesoporous ceria loaded with 0.06–0.93 wt% iridium was synthesized in one step by the ambient air combustion of an aqueous solution of ceric ammonium nitrate, ammonium hexachloroiridate, and glycine fuel. The structural properties of the powders, and the influence of such parameters as Ir loading and thermochemical post-treatments, were investigated combining aberration-corrected HRTEM, SEM, in situ XRD, XPS, DRIFTS, and Raman spectroscopy. The materials, which appeared spongy at the micrometer scale, exhibited ca. 30 nm-sized ceria crystallites with a layered structure at the nanoscale. After reducing treatments, Ir nanoparticles anchored at the surface of ceria grains were identified, and their size (ca. 2 nm) did not evolve upon further heating at up to 900 °C. A detailed picture of the Ir–CeO2 interface could be established, with the presence of Irx+–O2−–Ce3+ entities along with oxygen vacancies. The powders loaded with only 0.1 wt% Ir were successfully employed as catalysts for the production of hydrogen from methane and water in low-steam conditions at 750 °C. Due to their higher Ir dispersion and stronger Ir–CeO2 interaction, the combustion-synthesized materials outperformed their conventionally prepared counterparts in terms of activity and stability, making them promising as active catalytic layers for solid-oxide fuel cells integrating the gradual internal reforming concept. [ABSTRACT FROM AUTHOR]

Ge-containing ITQ-22 zeolites have been almost completely degermanated under strong acidic conditions without modifications of the framework topology. Simultaneous to Ge extraction, the framework was partially dissolved; mesopores were formed but the structure was maintained through the re-incorporation of some of silicon species at vacant sites. The presence of many defects in the degermanated framework enabled the incorporation of tetrahedral aluminum, opening the way to the preparation of new and stable acid catalysts with original topologies. [ABSTRACT FROM AUTHOR]

Ge-containing ITQ-22 zeolites have been almost completely degermanated under strong acidic conditions without modifications of the framework topology. Simultaneous to Ge extraction, the framework was partially dissolved; mesopores were formed but the structure was maintained through the re-incorporation of some of silicon species at vacant sites. The presence of many defects in the degermanated framework enabled the incorporation of tetrahedral aluminum, opening the way to the preparation of new and stable acid catalysts with original topologies. [ABSTRACT FROM AUTHOR]

Lignin is one of the main components of lignocellulosic biomass and corresponds to the first renewable source of aromatic compounds. It is obtained as a by-product in 100 million tons per year, mainly from the paper industry, from which only 2–3% is upgraded for chemistry purposes, with the rest being used as an energy source. The richness of the functional groups in lignin makes it an attractive precursor for a wide variety of aromatic compounds. With this aim, we investigated the Pd-catalyzed depolymerization of lignin under mild oxidizing conditions (air, 150 °C, and aqueous NaOH) producing oxygenated aromatic compounds, such as vanillin, vanillic acid, and acetovanillone. Palladium catalysts were implemented following different strategies, involving nanoparticles stabilized in water, and nanoparticles were supported on TiO2. Significant conversion of lignin was observed in all cases; however, depending on the catalyst nature and the synthetic methods, differences were observed in terms of selectivity in aromatic monomers, mainly vanillin. All these aspects are discussed in detail in this report, which also provides new insights into the role that Pd-catalysts can play for the lignin depolymerization mechanism. [ABSTRACT FROM AUTHOR]

We report an original and scalable synthesis pathway to produce encapsulated gold nanoparticles. Precise control of the gold particles is achieved in the range of 1–10 nm through the impregnation of silicalite-1 with a controlled concentration of gold solution, followed by dissolution–recrystallization of the zeolite. [ABSTRACT FROM AUTHOR]

An octylsilane-stabilized colloidal dispersion of 2 nm crystalline gold nanoparticles is highly active and selective for the aerobic oxidations of stilbene and cyclohexene in methylcyclohexane. [ABSTRACT FROM AUTHOR]

This study reports the catalytic properties of Ag nanoparticles dispersed on mixed ionic and electronic conducting layers of LSCF (La0.6Sr0.4Co0.2Fe0.8O3) for propene combustion. A commercial and a synthesized LSCF powder were deposited by screen-printing or spin-coating on dense yttria-stabilized zirconia (YSZ) substrates, an oxygen ion conductor. Equal loadings (50 µg) of Ag nanoparticles were dispersed via drop-casting on the LSCF layers. Electrochemical and catalytic properties have been investigated up to 300 °C with and without Ag in a propene/oxygen feed. The Ag nanoparticles do not influence the electrochemical reduction of oxygen, suggesting that the rate-determining step is the charge transfer at the triple phase boundaries YSZ/LSCF/gas. The anodic electrochemical performances correlate well with the catalytic activity for propene oxidation. This suggests that the diffusion of promoting oxygen ions from YSZ via LSCF grains can take place toward Ag nanoparticles and promote their catalytic activity. The best specific catalytic activity, achieved for a LSCF catalytic layer prepared by screen-printing from the commercial powder, is 800 times higher than that of a pure Ag screen-printed film. [ABSTRACT FROM AUTHOR]