Showing papers on "Catalyst support published in 1992"

Thin-film catalyst layers for polymer electrolyte fuel cell electrodes

Abstract: New structures for the Pt/C catalyst layer of polymer electrolyte fuel cell electrodes have been developed that substantially increase the utilization efficiency of the catalyst. Fabricating the catalyst layers and gas diffusion backings separately makes it possible to formulate each structure with the properties that are most suitable for its function. In the case of the catalyst layer, the optimal properties are hydrophilicity, thinness, uniformity, and the proper ratio of ionomer and supported catalyst. The catalyst layers are cast from solution as thin films that utilize the ionomer itself as a binder. The thin films are hot pressed directly onto the ionomer membranes, and the hydrophobic gas diffusion backings are inserted when the cells are assembled. The performances of fuel cells based on the thin film catalyst layers are comparable with those of gas diffusion electrode designs that utilize several times as much platinum, thus the specific activities of the Pt catalysts in the new structures are significantly higher.

Supercritical phase fischer‐tropsch synthesis: Catalyst pore‐size effect

Abstract: The Fischer-Tropsch synthesis reaction was conducted in a supercritical fluid medium using a fixed-bed reactor. Tailor-made catalyst supports which had sharp pore diameter distributions were prepared by the pH swing method. The relationships between the catalyst pore structure and the catalytic activity or the product distribution were studied. The influence of the catalyst pore size on the mass transfer of reactants and products was also characterized. The catalyst pore size affected not only catalytic activity but also product selectivity. The diffusion of reactants inside the catalyst pellets in the supercritical fluid media was simulated and the effects of catalyst pore size and catalyst particle size on catalytic performances were consistent with simulation results.

Structural characterisation and optimisation of acid-treated montmorillonite and high-porosity silica supports for ZnCl2 alkylation catalysts

Abstract: The effect of acid treatment of montmorillonite clay on its activity as a support for ZnCl2 alkylation catalyst is examined. Maximum activity is associated with long acid treatment times. Structural characterisation, using X-ray diffraction (XRD), 29Si magic-angle-spinning nuclear magnetic resonance (MASNMR) and elemental analysis, suggests that there is little residual clay structure in the most active supports. A selection of commercially available high-porosity silicas are shown to be more active supports than the acid clays under study. Porosimetry measurements indicate that the presence of mesopores may be an important requirement for an effective ZnCl2 catalyst support.

Nature of the metal-support interface in supported metal catalysts: results from x-ray absorption spectroscopy

Abstract: X-ray absorption spectra characterizing the metal-support interface in supported metal complexes and supported metal catalysts are summarized and evaluated. Single-metal-atom transition metal complexes on non-reducible metal oxide supports are bonded with metal-oxygen bonds with metal-oxygen distances of approximately 2.15 A; the bonding distance is only weakly sensitive to the oxidation state of the metal. Nearly this same metal-oxygen distance is characteristic of the metal-support interface in metal-oxide-supported metal clusters following high temperature reduction in H2 (HTR:T > 450 °C). The metals at the interface may be polarized sufficiently that they bond with the oxygen of the support much as the cations in mononuclear complexes bond with it. When the supported metals are treated in H2 at low temperatures (LTR:T < 350 °C) or are prepared under He with partially hydroxylated supports, a longer metal-support oxygen distance is observed, typically 2.5–2.7 A. This distance is suggested to characterize interactions between zero-valent metals and support oxygen. Changes in the performance of supported metal catalysts resulting from differences in the temperature of pretreatment in H2 are attributed to changes in the electronic properties and/or morphology of the metal clusters, which are suggested to be related to the concomitant changes in the structure of the metal-support interface.

Bulk and surface analysis of a Fe-P-O oxydehydrogenation catalyst

Abstract: Combination of X-ray photoelectron spectroscopy and X-ray microprobe analysis gives complementary information on the composition and on the chemical state of the elements iron and phosphorus present in a Fe-P-O oxydehydrogenation catalyst. On the fresh catalyst iron is present mainly as Fe3+ species whereas after a typical test, which selectively transforms isobutyric acid to methacrylic acid, both Fe2+ and Fe3+ are present. Phosphorus, in comparison to iron, is not homogeneously distributed in the catalyst particles and there exists a phosphorus enrichment at the surface. Positive and negative charge balance reveal that hydrogen phosphate-like species are present in such a catalyst. This is consistent with the observation that this system is active with large amounts of water in the feed.

Catalysts and processes for the manufacture of vinyl acetate

Abstract: A shell impregnated catalyst for use in the production of vinyl acetate from ethylene, acetic acid and an oxygen containing gas is provided. The catalyst has a productivity of greater than 661 grams of vinyl acetate per hour per liter of catalyst at 150° C. and consists essentially of: (1) a catalyst support having a particle diameter from about 3 to about 7 mm and a pore volume of 0.2 to 1.5 ml per gram (2) palladium and gold distributed in the outermost 1.0 mm thick layer of the catalyst support particles, and (3) from about 3.5 to 9.5% by weight of potassium acetate. The catalyst is characterized by having a gold to palladium weight ratio in the range 0.60 to 1.25.

Deactivation of ruthenium catalysts in continuous glucose hydrogenation

Abstract: Several Ru/Al2O3 glucose hydrogenation catalysts were tested in continuous operation After use, spent catalysts were characterized by a variety of techniques to determine what changes had accompanied deactivation The ruthenium tended to agglomerate, and changes in the physical properties of the Al2O3 support were observed In addition, the buildup of iron, sulfur, and gluconic acid on the catalyst during use was detected Experimental data strongly implicate these changes in causing catalyst deactivation For example, when iron and gluconic acid poisoning is minimized, substantial improvements in catalyst stability are achieved

Catalyst deactivation during deep oxidation of chlorohydrocarbons

Abstract: A commercial chromia-alumina catalyst was investigated for an extended period of time for the oxidation of two gas streams containing volatile organic compounds (VOCs) with compositions similar to those expected from groundwater air strippers. The first gas stream ( chlorinated stream ) contained 500 ppm of C1 to C2 chlorohydrocarbons, while the second stream (mixed stream) contained 450 ppm of C5 to C9 hydrocarbons plus 50 ppm of trichloroethylene. Catalyst deactivation was studied at constant conversion of the main reaction, achieved by increasing the temperature, when needed, to compensate for the loss of intrinsic catalyst activity. The catalytic activity and selectivity were found to be a function of the type of feed stream and the reactor configuration. Although the catalyst used for the oxidation of the chlorinated stream did not require any temperature increase when used fore 153 days-on-stream in a fixed bed reactor, the results suggest progressive loss in catalyst activity down the catalyst bed. A fluid bed reactor was found to be more effective than a fixed bed reactor in maintaining the catalyst activity for the oxidation of the chlorinated stream. The physical attrition of catalyst particles in the fluid bed reactor accompanied with the loss of chromium, via oxychloride formation, appears to be beneficial in maintaining the catalyst activity by constantly exposing the fresh catalyst surface. The catalyst used for mixed stream oxidation required a temperature increase of 33°C over 210 days-on-stream to maintain constant conversion. This decrease in catalytic activity was related to a decrease in BET surface area.

Olefin polymerization solid catalyst, olefin polymerization catalyst and olefin polymerization

Abstract: The present invention relates to a solid catalyst composed of a specific solid catalyst component [A-1], the catalyst containing the solid catalyst and the olefin polymerization process using the solid catalyst, in which the solid catalyst component [A-1] comprises; (a-1) a particulate carrier composed of a specific oxide of a metal; (a-2) an organoaluminum oxy compound; and (a-3) a specific transition metal compound containing a specific ligand, wherein the organoaluminum oxy compound (a-2) and the transition metal compound (a-3) are supported on the particulate carrier (a-1) . The catalysts are applicable to a suspension polymerization and a vapor phase polymerization, and capable of preparing spherical olefin polymers excellent in particle characteristics at high polymerization activity.

Methanol Oxidation on Platinum‐Tin Catalysts Dispersed on Poly(3‐methyl)thiophene Conducting Polymer

Abstract: Platinum-tin catalysts were prepared by electrodeposition on poly(3-methyl)thiophene to investigate the effect of catalyst support and Pt loading on the electrochemical oxidation of methanol. The polymer-catalyst assembly was characterized by SEM/EDX, surface area measurements, and Rutherford backscattering spectrometry (RBS). The Pt-Sn catalyst deposited in the hydrogen adsorption potential region showed an order of magnitude higher surface area. RBS studies enabled the estimation of the thickness and the distribution of the catalyst layer in the conducting polymer support

Hydroisomerization of n-pentane over hybrid catalysts containing a supported hydrogenation catalyst

Abstract: Isomerization of n-pentane to iso-pentane was studied on a series of ZSM-5 zeolite catalysts under hydrogen and nitrogen atmosphere. A H-ZSM-5 catalyst showed low n-pentane conversion and isopentane selectivity. A Pt-ZSM-5 catalyst prepared using an ion-exchange method showed high activity and high iso-pentane selectivity reaching an equilibrium conversion. A hybrid catalyst prepared by physically mixing H-ZSM-5 and Pt/SiO2 showed high activity and selectivity equal to those of Pt/ZSM-5 while Pt/SiO2 and H-ZSM-5 had a poor catalytic performance for this reaction. A hybrid catalyst containing palladium showed high activity and selectivity but a palladium ion-exchanged ZSM- 5 catalyst did not. With the hybrid catalyzed reaction, the mixing state of H-ZSM-5 and Pt/SiO2 had a strong influence on the activity and iso-pentane selectivity. In the absence of hydrogen, the conversion of n-pentane was dramatically reduced and the oligomerization reaction became dominant. These results suggest that spilled-over hydrogen plays an important role in alkane activation and the stabilization of intermediates.

Improved catalyst composition

Abstract: An addition polymerization catalyst comprising a cationic complex of a Group 4 metal cyclopentadienyl derivative and an alumoxane shows improved resistance to catalyst poisons.

Mixed chromium catalysts and polymerizations utilizing same

Abstract: Mixed catalyst compositions comprised of a first supported chromium-containing catalyst component and a second supported chromium-containing catalyst component and which additionally have one or more metallic or non-metallic catalytic agents associated therewith are provided. The additional metallic or non-metallic elements associated with the catalyst components can be aluminum, titanium, zirconium, boron, phosphorous or combinations thereof. The pore volume of the silica supports used for the first and second catalyst components differs by at least 0.3 cc/g. The mixed catalyst compositions of the invention are useful for the preparation of polyolefins. They are particularly useful of polymerization of ethylene in particle form polymerizations to produce high density polyethylene blow molding resins having good processability and physical properties. The improved particle form polymerization process and products obtained thereby using the above-described mixed catalyst compositions are also described.

Catalytic conversion with improved catalyst catalytic cracking with a catalyst comprising a large-pore molecular sieve component and a ZSM-5 component

Abstract: A process is provided for converting feedstock hydrocarbon compounds over a catalyst composition which comprises a large-pore molecular sieve material and an additive catalyst composition comprising crystalline material having the structure of ZSM-5 and a silica/alumina mole ratio of less than about 30. An embodiment of the present invention comprises an improved catalytic cracking process to produce high octane gasoline, increased alkylate and potential alkylate, and increased lower olefins, especially propylene.

Catalytic oxidation of aqueous organic contaminants

Abstract: A catalyst for oxidizing aqueous organic contaminants includes about 5 wt % to about 20 wt % noble metal crystallites selected from the group consisting of platinum, palladium, ruthenium, iridium, and combinations thereof deposited on a high surface area catalyst support. The crystallites are about 100 Å or smaller. A system for catalytically oxidizing aqueous organic contaminants has a catalyst bed containing such a catalyst, means for heating a reactor feed stream to a desired reaction temperature, means oxygenating the feed stream, and a phase separator for separating gaseous reaction products from a reactor effluent stream.

Polymerization catalyst for olefines

Abstract: The present invention concerns a polymerization catalyst of olefins, said catalyst containing an active chromium compound on an inorganic support. The catalyst in accordance with the invention is prepared by vaporizing a precursor of chromium oxide such as chromyl chloride and allowing the chromium oxide vapor to react with the surface of, e.g., silica gel support material at 160° . . . 500° C. A selective binding of the chromium oxide to the support material is achieved by keeping the vapor pressure sufficiently high and the duration of interaction with the support sufficiently long so as to maintain an excess of the chromium compound in relation to the number of available binding sites on the support material. The activity of a catalyst in accordance with the invention even with a very low content of catalytic metal is as high as the activity of a catalyst of an appreciably higher metal content that has been prepared by the methods of the conventional technology.

Oxidation catalyst resistant to sulfation

Abstract: A sulfur resistant CO, hydrocarbon and SOx oxidation catalyst is provided comprising silica particles which have been coated with titania or zirconia or precursors thereof and which have deposited thereon a precious metal such as platinum. The coated silica catalyst can be included in a washcoat for application to a ceramic honeycomb carrier.

Characteristics of carbon-supported palladium catalysts for liquid-phase hydrogenation of nitroaromatics

Abstract: Effects of the properties of support and the preparation condition on the characteristics of carbon-supported palladium catalysts were investigated. The characteristics included dispersion and distribution of metal and the catalytic activity on the liquid-phase hydrogenation of dinitrotoluene. Oxidation of carbon support appeared to increase the number of surface oxygen groups and to enhance dispersion of palladium. However, the catalytic activity did not improve in proportion to the dispersion. In carbon-metal salt slurry, nuclei formation and growth by ion exchange and/or reduction was considered to be the most important step in determining the final state of the catalysts prepared by the alkali hydrolysis method. The catalytic activity was found to be strongly dependent on metal location throughout the mesopore structure especially in the case of catalysts supported on highly porous activated carbon

Selective oxidation of methane with air over silica catalysts

Abstract: Partial oxidation of methane by oxygen to form formaldehyde, carbon oxides, and C2 products (ethane and ethene) has been studied over silica catalyst supports (fumed Cabosil and Grace 636 silica gel) in the 630–780 °C temperature range under ambient pressure. The silica catalysts exhibit high space time yields (at low conversions) for methane partial oxidation to formaldehyde, and the C2 hydrocarbons were found to be parallel products with formaldehyde. Short residence times enhanced both the C2 hydrocarbons and formaldehyde selectivities over the carbon oxides even within the differential reactor regime at 780 °C. This suggests that the formaldehyde did not originate from methyl radicals, but rather from methoxy complexes formed upon the direct chemisorption of methane at the silica surface at high temperature. Very high formaldehyde space time yields (e.g., 812 g/kg cat h at the gas hourly space velocity = 560 000 l(NTP)/kg cat h) could be obtained over the silica gel catalyst at 780 °C with a methane/air mixture of 1.5/1. These yields greatly surpass those reported for silicas earlier, as well as those over many other catalysts. Low CO2 yields were observed under these reaction conditions, and the selectivities to formaldehyde and C2 hydrocarbons were 28.0 and 38.8%, respectively, at a methane conversion of 0.7%. A reaction mechanism was proposed for the methane activation over the silica surface based on the present studies, which can explain the product distribution patterns (specifically the parallel formation of formaldehyde and C2 hydrocarbons).