Inverse gas chromatographic investigation of the effect of hydrogen in carbon monoxide adsorption over silica supported Rh and Pt-Rh alloy catalysts, under hydrogen-rich conditions

Selective CO oxidation (SCO) has attracted scientific and technological interest due to its application to the operation of proton electrolyte membrane fuel cells (PEM-FCs). CO adsorption, being an elementary step of SCO, is studied over silica supported monometallic Rh and Rh0.50 + Pt0.50 alloy catalysts, under various hydrogen atmospheres, namely: 25% H2 + 75% He, 50% H2 + 50% He and 75% H2 + 25% He carrier gas mixture compositions. The investigation of CO adsorption is done by utilizing reversed-flow gas chromatography (RF-GC). As a result rate constants for the adsorption (k1), desorption (k(-1)) and irreversible CO binding (k2) over the studied catalysts as well as the respective activation energies are determined. The variation of the rate constants and the activation energies against the nature of the used catalyst (monometalic or alloy) and the amount of hydrogen in the carrier gas gives useful information for the selectivity as well as the activity of CO oxidation over group VIII noble metals. At low temperatures and under H2-rich conditions compatible with the operation of PEM fuel cells the activity of the monometallic and the alloy catalysts is expected to be similar, however the selectivity of Rh0.50 + Pt0.50 alloy catalyst is expected to be higher, making Pt-Rh alloy catalyst as a better candidate for CO preferential oxidation (PROX). The low energy barrier values found in the present work, most likely are referred to high surface amounts of CO. The desorption barriers determined are in any case much lower than the respective activation energies found for CO desorption in the absence of hydrogen indicating a H2-induced desorption, which can explain the observed in the literature rate enhancement of SCO oxidation.     

High Catalytic Efficiency of a Nanosized Copper-Based Catalyst for Automotives: A Physicochemical Characterization

The global trend in restrictions on pollutant emissions requires the use of catalytic converters in the automotive industry. Noble metals belonging to the platinum group metals (PGMs, platinum, palladium, and rhodium) are currently used for autocatalysts. However, recent efforts focus on the development of new catalytic converters that combine high activity and reduced cost, attracting the interest of the automotive industry. Among them, the partial substitution of PGMs by abundant non-PGMs (transition metals such as copper) seems to be a promising alternative. The PROMETHEUS catalyst (PROM100) is a polymetallic nanosized copper-based catalyst for automotives prepared by a wet impregnation method, using as a carrier an inorganic mixed oxide (CeO₂-ZrO₂) exhibiting elevated oxygen storage capacity. On the other hand, catalyst deactivation or ageing is defined as the process in which the structure and state of the catalyst change, leading to the loss of the catalyst’s active sites with a subsequent decrease in the catalyst’s performance, significantly affecting the emissions of the catalyst. The main scope of this research is to investigate in detail the effect of ageing on this low-cost, effective catalyst. To that end, a detailed characterization has been performed with a train of methods, such as SEM, Raman, XRD, XRF, BET and XPS, to both ceria–zirconia mixed inorganic oxide support (CZ-fresh and -aged) and to the copper-based catalyst (PROM100-fresh and -aged), revealing the impact of ageing on catalytic efficiency. It was found that ageing affects the Ce–Zr mixed oxide structure by initiating the formation of distinct ZrO₂ and CeO₂ structures monitored by Raman and XRD. In addition, it crucially affects the morphology of the sample by reducing the surface area by a factor of nearly two orders of magnitude and increasing particle size as indicated by BET and SEM due to sintering. Finally, the Pd concentration was found to be considerably reduced from the material’s surface as suggested by XPS data. The above-mentioned alterations observed after ageing increased the light-off temperatures by more than 175 °C, compared to the fresh sample, without affecting the overall efficiency of the catalyst for CO and CH₄ oxidation reactions. Metal particle and CeZr carrier sintering, washcoat loss as well as partial metal encapsulation by Cu and/or CeZrO₄ are identified as the main causes for the deactivation after hydrothermal ageing.     

Analysis of post-Byzantine icons from the Church of the Assumption in Cephalonia, Ionian Islands, Greece: a multi-method approach

A multi-method approach has been developed for the characterisation of the proteinaceous binding media, drying oils and pigments present in samples from the panel paintings of the Church of the Assumption in Cephalonia (Ionian Islands, Greece). The analytical protocol involved the use of scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), Raman spectroscopy and gas chromatography. The identification of the pigments was achieved by SEM/EDX and Raman spectroscopy. The latter technique was also used for the detection of the binding media, while their characterisation was achieved by gas chromatographic analysis of ethyl chloroformate derivatives. The aim of this multi-method protocol was to obtain as much information as possible from the panel paintings of the Church of the Assumption, through non-destructive methods, before proceeding to gas chromatography. Little scientific information is available for the understanding of the construction technique and the materials used by the post-Byzantine artists and whatever is available comes mainly from artists’ manuals. One of the aims of this paper is to provide a scientific background to the technology of the Ionian post-Byzantine icons.     

Category-Theoretic Interpretative Framework of the Complementarity Principle in Quantum Mechanics

This study aims to provide an analysis of the complementarity principle in quantum theory through the establishment of partial structural congruence relations between the quantum and Boolean kinds of event structure. Specifically, on the basis of the existence of a categorical adjunction between the category of quantum event algebras and the category of presheaves of variable Boolean event algebras, we establish a twofold complementarity scheme consisting of a generalized/global and a restricted/local conceptual dimension, where the latter conception is subordinate to and constrained by the former. In this respect, complementarity is not only understood as a relation between mutually exclusive experimental arrangements or contexts of comeasurable observables, as envisaged by the original conception, but it is primarily comprehended as a reciprocal relation concerning information transfer between two hierarchically different structural kinds of event structure that can be brought into partial congruence by means of the established adjunction. It is further argued that the proposed category-theoretic framework of complementarity naturally advances a contextual realist conceptual stance towards our deeper understanding of the microphysical nature of reality.

     

Background spectral characteristics in direct sample insertion-inductively coupled plasma-mass spectrometry

An extensive set of background spectra are presented for a direct sample insertion-inductively coupled plasma-mass spectrometer (DSI-ICP-MS) system. These include spectra of a dry plasma (i.e. one in which no sample or solvent is introduced) and background spectra for DSI sample probes such as graphite, Mo and Ta cups as well as a W wire loop. Compared to the background spectra measured when aqueous solutions are nebulized into the plasma the DSI background spectra are considerably simpler. Primarily due to the elimination of water in DSI systems there is a significant reduction and even elimination of numerous background species, particularly those containing oxygen and hydrogen. In addition, the DSI sample probes themselves do not add any complex species to the spectral background.     

The cycloaddition of diethyl chlorophosphite with norbornadiene: Synthesis and crystal structure of the cycloadduct.

In the presence of Lewis acids, diethyl phosphorochloridite reacts with norbornadiene to afford the tetracyclic phosphinate ester 3 . The reaction is believed to involve formation of phosphenium ions stabilized only by alkoxy substituents. The cycloadduct of the reaction was characterized by its spectral data, by single crystal diffraction analysis of the parent acid, and ³¹P and ²⁷Al nmr experiments.     

Assignment of stereochemistry to cyclohexenylidenecyanoacetates by 1H NMR spectroscopy

The stereochemistry of various pairs of isomeric 2-cyclohexen-1-ylidenecyanoacetates was assigned using ¹H NMR spectroscopy. The isomers with the γ-methylene or the γ-vinyl protons cis to the carbalkoxy group were found to have the signals of these protons at approximately 0.3 ppm and 1 ppm, respectively, downfield relative to their geometrical isomers or the corresponding 2-cyclohexen-1-ylidenemalononitriles. The observation regarding the γ-vinyl proton proved useful for the assignment of configuration to cyclohex-enylidenecyanoacetates derived form cholest-4-en-3-one. The large and constant downfield shift (c. 1 ppm) of the γ-vinyl proton when cis to the ester group results from the rigid cyclohexenylidenecyanoacetate system, in which the vinylic proton can approach more closely to the magnetically anisotropic ester carbonyl group.     

Heteroannulation of naphthoquinones. Studies on the reaction of 2-bromo-2,3-dihydronaphthoquinone derivatives with 1,2-binucleophiles.

Heterocyclic derivatives of naphthoquinones were synthesized via their 2-bromo-2,3-dehydro-intermediates. This new route may lead to the formation of benzo[a]phenothiazin-5-ones, benzo[f]quinoxalin-6-ones as well as their 1,4 (or 7,10) dihydroxy-derivatives in high yields. The possible mechanisms involved in the formation of these compounds are discussed.     

Synthesis and characterization of 3D CoPt nanostructures

Cobalt platinum polypod-like nanostructures were synthesized by thermolytic reduction of Pt(acac)2 and Co(CH3COO)2 in oleylamine at 250 degrees C. The as-made CoPt nanopolypods are ferromagnetic, are soluble in nonpolar organic solvents, and reveal a coercive field of 525 and 1200 Oe at room temperature and 5 K, respectively.