Comparing Catalysts of the Direct Synthesis of Hydrogen Peroxide in Organic Solvent: is the Measure of the Product an Issue?

The direct synthesis of hydrogen peroxide has been for about 20 years a hot topic in \u201cgreen\u201d 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

Changes in the flexion relaxation response induced by lumbar muscle fatigue

<p>Abstract</p> <p>Background</p> <p>The flexion relaxation phenomenon (FRP) is an interesting model to study the modulation of lumbar stability. Previous investigations have explored the effect of load, angular velocity and posture on this particular response. However, the influence of muscular fatigue on FRP parameters has not been thoroughly examined. The objective of the study is to identify the effect of erector spinae (ES) muscle fatigue and spine loading on myoelectric silence onset and cessation in healthy individuals during a flexion-extension task.</p> <p>Methods</p> <p>Twenty healthy subjects participated in this study and performed blocks of 3 complete trunk flexions under 4 different experimental conditions: no fatigue/no load (1), no fatigue/load (2), fatigue/no load(3), and fatigue/load (4). Fatigue was induced according to the Sorenson protocol, and electromyographic (EMG) power spectral analysis confirmed that muscular fatigue was adequate in each subject. Trunk and pelvis angles and surface EMG of the ES L2 and L5 were recorded during a flexion-extension task. Trunk flexion angle corresponding to the onset and cessation of myoelectric silence was then compared across the different experimental conditions using 2 × 2 repeated-measures ANOVA.</p> <p>Results</p> <p>Onset of myoelectric silence during the flexion motion appeared earlier after the fatigue task. Additionally, the cessation of myoelectric silence was observed later during the extension after the fatigue task. Statistical analysis also yielded a main effect of load, indicating a persistence of ES myoelectric activity in flexion during the load condition.</p> <p>Conclusion</p> <p>The results of this study suggest that the presence of fatigue of the ES muscles modifies the FRP. Superficial back muscle fatigue seems to induce a shift in load-sharing towards passive stabilizing structures. The loss of muscle contribution together with or without laxity in the viscoelastic tissues may have a substantial impact on post fatigue stability.</p

Polymer Frameworks as Templates for Generating Size-Controlled Metal Nanoclusters. Synthetic Aspects and Relevance to Supported Metal Catalysis

This work deals with polymer frameworks as templates for generating size-controlled metal nanoclusters. Synthetic aspects and relevance to supported metal catalysis

Cross-Linked Polymers as Scaffolds for the Low-Temperature Preparation of Nanostructured Metal Oxides

The 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

Generation 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"

In 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

Synthesis and characterization of Iron(III) oxides as supports for Au(0)-based catalysts

A series of iron(III) hydrated oxide/oxyhydroxide/oxide was prepared by precipitation from Fe(III) aqueous solutions, to obtain supports suitable as Au(0)-based catalysts. During synthesis, all parameters -pH, temperature and adding rate - were strictly controlled in order to achieve highly reproducible synthesis. The method of purification was also planned in order to remove nitrate ions that can influence the catalytic activity and/or the support properties, without modifying the structure or particle dimension of the support. Dialysis was identified as the best method for purifying the hydrated oxide/hydroxide, i.e., ferrihydrite and goethite; while ammonium carbonate washing proved to be the most successful for the other hydroxide/oxides. Mossbauer spectroscopy and X-ray powder diffraction pointed out the complexity of all these systems, proving the extreme importance of synthesis temperature for crystallinity, particle dimension, and amount of hydroxide/oxid

Generation of size-controlled Pd-0 nanoclusters inside nanoporous domains of gel-type resins: Diverse and convergent evidence that supports a strategy of template-controlled synthesis

TEM, XRD characterization of palladium nanoparticles reveal a particle size distribution strongly related to the porosity (determined with Inverse Size Exclusion chromatography) of the swollen gel type resin employed as the stabilizing agent. These evidences suggest that the morphology of the polymer resin has a key role in the determination of the particles size