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Catalyst Support (catalyst + support)
Selected AbstractsCarbon-Carbon Double Bond versus Carbonyl Group Hydrogenation: Controlling the Intramolecular Selectivity with Polyaniline-Supported Platinum CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2008Martin Steffan Abstract The use of polyaniline (PANI) as catalyst support for heterogeneous catalysts and their application in chemical catalysis is hitherto rather poorly known. We report the successful synthesis of highly dispersed PANI-supported platinum catalysts (particle sizes between 1.7 and 3.7,nm as revealed by transmission electron microscopy, TEM) choosing two different approaches, namely (i) deposition-precipitation of H2PtCl6 onto polyaniline, suspended in basic medium (DP method) and, (ii) immobilization of a preformed nanoscale platinum colloid on polyaniline (sol-method). The PANI-supported platinum catalysts were applied in the selective hydrogenation of the ,,,-unsaturated aldehyde citral. In order to benchmark their catalytic performance, citral hydrogenation was also carried out by using platinum supported on the classical support materials silica (SiO2), alumina (Al2O3), active carbon and graphite. The relations of the structural characteristics and surface state of the catalysts with respect to their hydrogenation properties have been probed by EXAFS and XPS. It is found that the DP method yields chemically prepared PtO2 on polyaniline and, thus, produces a highly dispersed and immobilized Adams catalyst (in the ,-PtO2 form) which is able to efficiently hydrogenate the conjugated CC bond of citral (selectivity to citronellal=87%), whereas reduction of the CO group occurs with polyaniline-supported platinum (selectivity to geraniol/nerol=78%) prepared via the sol-method. The complete reversal of the selectivity between the preferred hydrogenation of the conjugated CC or CO group is not only particularly useful for the selective hydrogenation of ,,,-unsaturated aldehydes but also unveils the great potential of conducting polymer-supported precious metals in the field of hitherto barely investigated chemical catalysis. [source] Creation of a Monomeric Ruthenium Species on the Surface of Micro-Size Copper Hydrogen Phosphate: An Active Heterogeneous Catalyst for Selective Aerobic Oxidation of AlcoholsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2007Junhua Liu Abstract A new micro-size copper hydrogen phosphate (CHP) synthesized by the emulsion method combined with a monomeric ruthenium species was found to be a very effective catalyst for the selective oxidation of alcohols. Several kinds of alcohols were transformed into the corresponding aldehydes or ketones over the RuCHP catalyst by oxygen under very mild conditions. The results showed that the CHP material was perfect as a catalyst support due to its high ion-exchange ability and adsorption capacity. [source] Spatial near-infrared imaging of hydroxyl band coverage on ceria-based catalystsAICHE JOURNAL, Issue 4 2006Farid Aiouache Abstract High-throughput near-infrared imaging was used to distinguish catalyst activity for low-temperature methane steam-reforming. Geminal hydroxyls of reduced ceria were depicted during methane reforming at 673 K. The changes in absorbance maps under various water partial pressures showed evidence of formate intermediate formations without redox exchanges. Higher resolution was observed in absorbance change images than that of thermal images obtained from catalyst surface self-emissions. The experimental results illustrated higher activity of pure rhodium catalyst than that of bimetallic ones, likely because of the high dispersion of rhodium on the catalyst support. Moreover, the reaction was accelerated when high surface area silica was added because more reduced sites were exposed. Our filter bandwidths limited our interest in band-shift distribution of geminal hydroxyl band during the reduction process. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Paolo Colombo Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers. (2) Special microstructural features of PDCs. (3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines. (4) Processing strategies to fabricate ceramic components from preceramic polymers. (5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available. [source] Hollow Alumina Microsphere Chain NetworksJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009Weiyou Yang Hollow Al2O3 microsphere chain networks have been synthesized via a simple two-staged pyrolysis of a precursor using active carbon powders as the template. The obtained networks are characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The chain networks are formed by subsequent aggregation of the prior formed hollow Al2O3 microspheres. The obtained chain networks are promising for the applications in catalyst support, filtration, and other applications due to their lightweight and highly porous nature. [source] Single-walled carbon nanotube/ultrahigh-molecular-weight polyethylene composites with percolation at low nanotube contentsPOLYMER ENGINEERING & SCIENCE, Issue 12 2009Brian P. Grady To mix single-walled carbon nanotubes (SWCNTs) with a polymer and to achieve low percolation thresholds, a low-viscosity liquid has been required in order to achieve sufficiently good dispersion. In this article, data are presented which show that percolation occurs at ,0.14 wt % carbon nanotubes and the dispersion procedure does not involve dispersing the SWCNTs in a low-viscosity liquid. Specifically, ultrahigh-molecular-weight polyethylene powder was mixed with a powder containing nanotubes and catalyst support, e.g., the powder contains 93% silica and 7% SWCNTs. The powder blend is compression molded into sheets using high pressure and temperature. Because of the very high viscosity of the resin, the nanotube/silica mixture largely stays segregated at the interface as shown by scanning electron microscopy. A significant drop in tensile properties (modulus, tensile strength, and elongation at break) occurs with filler incorporation. Non isothermal crystallization measurements indicate that this filler does not nucleate crystallinity when mixed in this manner; although there is a definite sharpening of the melt endotherm indicating that crystallites with smaller lamellar thicknesses are reduced significantly with filler addition. The addition of filler also slightly reduces the overall fractional crystallinity measured after a constant cooling rate. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] | |||||||||||||