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Versatile plug flow catalytic cell for in situ transmission/fluorescence x-ray absorption fine structure measurements
No full textCross-Linked Polymers as Scaffolds for the Low-Temperature Preparation of Nanostructured Metal Oxides
No full textThe current state of the art of the use of cross-linked organic polymers, both insoluble (resins or gels) and soluble (micro- and nanogels), as aids for the low-temperature preparation of stable metal oxide nanoparticles or nanostructured metal oxides is reviewed herein. Synthetic strategies for inorganic oxide nanomaterials of this kind can greatly benefit from the use of cross-linked polymers, which may act as scaffolds/exotemplates during inorganic nanoparticle synthesis, or as stabilizers following post-synthetic modification of the nanoparticles. Furthermore, the peculiar properties of the organic cross-linked polymers add to those of the inorganic oxide nanoparticles, producing materials with combined properties. The potential applications of such highly promising composite nanomaterials will be also briefly sketched
Comparing Catalysts of the Direct Synthesis of Hydrogen Peroxide in Organic Solvent: is the Measure of the Product an Issue?
Full text linkThe direct synthesis of hydrogen peroxide has been for about 20 years a hot topic in “green” catalysis. Several methods, which are well established to measure the concentration of hydrogen peroxide in water are also applied to the analysis of reaction mixtures from the direct synthesis of H2O2. However, this step could not be always straightforward, because these mixtures contain almost invariably organic solvents and, sometimes, selectivity enhancers which can interfere in some, at the least, of the most popular titrimetric methods. This work presents a comparative investigation of iodometry, cerimetry, permanganometry (titrimetric methods) and spectrophotometric analysis of TiIV/H2O2 adduct, as applied to analysis of hydrogen peroxide produced by its direct synthesis. They account for more than 90 % of the competent literature since 2000. Their pros and cons are highlighted to provide a guideline for the choice of the best possible method of analysis and for the comparison of catalytic results assessed in different ways in the context of the direct synthesis of hydrogen peroxide
Resonant-XRD characterization of nanoalloyed Au-Pd catalysts for the direct synthesis of H2O2: Quantitative analysis of size dependent composition of the nanoparticles
Full text linkThe focus of this work is on the relationship between the quantitative structural characterization of bimetallic Au-Pd nanoparticles dispersed in an amorphous polymer matrix and their catalytic activity in the direct synthesis of hydrogen peroxide (DS reaction). Resonant X-ray powder diffraction with synchrotron radiation was employed to probe selectively and to reveal fine details of the structure of bimetallic nanoparticles embedded in the support. The semi-quantitative analysis of the resonant X-ray powdered diffraction data, made on a large number of metal nanoparticles, shows that in one of the polymer-supported Au-Pd catalyst for the DS reaction (P75) featured by an overall molar Pd/Au of about 5.54, the smallest metal nanoparticles (MNPs), which account for more than 99.9% of the total MNPs number and for more than 95% of the metal surface, are formed by practically pure palladium. The relative number of bimetallic alloyed nanoparticles is very small (less than 4 x 10(2) ppm) and they contribute to only about 2% of the total metal surface. In a second gold-enriched catalyst (P50) with an overall molar Pd/Au of 1.84, the proportion of the bimetallic alloyed nanoparticles increased to about 97% and they account for about 99% of the metal surface. As a result of the metal intermixing, the catalytic productivity for the DS reaction increased from 97 to 109 mmol(H2)O(2)/mol(H2), owing to the gold-promotion of palladium
Polymer-Hematite Nanocomposites: Templating Effect of Commercial Ion-Exchangers in the Growth of Size-Controlled Iron Oxide Nanoparticles
No full textGeneration of size-controlled Pd0 nanoclusters inside of the nanoporous domains of gel-type resins: diverse and convergent support to a strategy of "Template Controlled Synthesis"
No full textIn the realm of supported metal catalysis, the metal component
is usually present as nanoparticles dispersed on the
surface of suitable metal oxides or on active carbon.
Synthetic procedures are normally directed to the generation
of size-controlled metal nanoclusters, whose circumstances
become mandatory when reactions to be catalyzed are
“structure sensitive”.In general, size control has been achieved by: directly
manufacturing metal-oxide-supported catalysts;by the
generation of kinetically stabilized metal nanoclusters in the
liquid phase and subsequent transfer of the protected
nanoclusters on to suitable supports; by generating metal
nanoclusters inside isoporous inorganic materials such as
mesoporous silicas. Herein, we report on three independent, convergent
pieces of structural evidence of this template-controlled
synthesis strategy to obtain size-controlled metal nanoclusters
suitable for synthesizing resin-supported metal catalysts
Template Controlled Synthesis of MonometallicZerovalent Metal Nanoclusters inside Cross-linked Polymer Frameworks: the Effect ofa Single Matrix on the Size of different Metal Nanoparticles
No full textGel-Type Cross-Linked Functional Polymers as Template in the synthesis of Size Controlled Metal Nanoclusters
No full textStructural characterization of 3d metal adsorbed AgNPs
No full textSilver nanoparticles AgNPs having small (6–8 nm) diameter, were synthesized in water in solutions and left interacting with diluted 3d metals (Co2+ or Ni2+ ions) solution (1–5 ppm range). The interactions between AgNPs and the metallic ions modify the optical response of the nanoparticles demonstrating their ability to capture metallic ions from water and making them valuable as metal contamination sensor. Here the coordination chemistry of Co and Ni adsorbed onto AgNPs is probed combining X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS)
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