RESUMO
Dry reforming of methane (DRM) enables an efficient utilization of two abundant greenhouse gases by converting them into syngas, a versatile feedstock for chemical synthesis. Aiming for high catalyst performance and enhanced coke resistance, different preparation techniques of La-promoted Ni/γ-Al2O3 catalysts for DRM were compared facilitating structure-performance correlations. The studied synthesis techniques comprehend incipient wetness impregnation and co-precipitation as well as alternative techniques such as spray drying. All catalysts were fully characterized before and after reaction by N2-physisorption, XRD, H2-TPR and STEM-EDX elemental mapping. Additionally, a thorough investigation of carbon deposits has been carried out by TGA/DSC and STEM-EDX, respectively. The different preparation techniques led generally to very different physical properties, structure, chemical species and anti-coking properties of the catalyst. However, some catalysts with similar physicochemical characteristics differed in catalytic performance and coking resistance. Superior catalytic performance could be reached for catalysts prepared by spray drying and related to excellent Ni dispersion, strong metal-support interaction and very low coke formation of only 2.7% of the catalyst weight. After 6 h time on stream only minor sintering occurred, with few Ni nanoparticles up to 10 nm.
RESUMO
The immobilization of molecular catalysts on support materials enables the combination of easy separation of solid catalysts with the high activity and selectivity of molecular catalysts. We have been able to apply a cross-metathesis reaction between terminal olefins, as versatile tool with which to reversibly immobilize ligands and complexes on a support material. Diphosphine ligands and corresponding complexes can be covalently immobilized and then split again from the support material after use in catalytic reactions, and subsequently be reused by repeated immobilization. The method is widely applicable and offers, therefore, an interesting approach to a covalent, but reversible immobilization of various molecular catalysts.
RESUMO
Reverse w/o microemulsions composed of methyl methacrylate (MMA) forming the oil phase, nonionic surfactants, and water are used for the synthesis of transparent SiO2/PMMA nanocomposites. An inorganic precursor, tetraethoxysilane (Si(OEt)(4), TEOS), is hydrolyzed in the reverse micelles containing aqueous ammonia. During the hydrolysis of TEOS, polymerization of the continuous MMA phase is initiated using AIBN (azobisisobutyronitrile), and after thermal polymerization at 333 K for 12 h, solid blocks of PMMA are obtained in which nanometer-sized silica particles are trapped in the solid polymer matrix. According to small-angle X-ray and dynamic light scattering experiments, the water droplets in MMA microemulsions are 12 nm (R(W) = 13) in diameter, whereas after polymerization of the microemulsion, the SiO2 particles in the transparent SiO2/PMMA composites are 26 nm in diameter. Transmission electron micrographs demonstrate a low degree of agglomeration in the composites. In comparison with materials generated from micelle-free solutions, the particle size distribution is narrow. The reverse micelle-mediated approach produces composites of high transparency comparable with that of pure PMMA.
RESUMO
High throughput transducers using metal cluster resonance technology are based on surface-enhancement of metal cluster light absorption. These devices can be used for detection of biorecognitive binding, as well as structural changes of nucleic acids, proteins or any other polymer. The optical property for the analytical application of metal cluster films is the so-called anomalous absorption. An absorbing film of clusters positioned 10--400 nm to a mirror surface reacts in a similar way to a reflection filter. At a certain distance of the absorbing layer to the mirror the reflected electromagnetic field has the same phase at the position of the absorbing cluster as the incident fields. This feedback mechanism strongly enhances the effective cluster absorption coefficient. The system is characterised by a narrow reflection minimum whose spectral position shifts sensitively with the interlayer thickness, because a given cluster-mirror distance and wavelength defines the optimum phase. Based on this principle a set of novel tools including biochips and micro arrays is presented, which enabled us to transduce binding, as well as changes of protein-, DNA- and polymer-conformation, quantitatively into an optical signal which can be observed directly as a colour change of a sensor-chip surface.
