Showing papers on "Catalyst support published in 1998"

Design of a Surface Alloy Catalyst for Steam Reforming

Abstract: Detailed studies of elementary chemical processes on well-characterized single crystal surfaces have contributed substantially to the understanding of heterogeneous catalysis. Insight into the structure of surface alloys combined with an understanding of the relation between the surface composition and reactivity is shown to lead directly to new ideas for catalyst design. The feasibility of such an approach is illustrated by the synthesis, characterization, and tests of a high-surface area gold-nickel catalyst for steam reforming.

Carbons as supports for industrial precious metal catalysts

Abstract: This review deals with the use of activated carbon, carbon black and graphite as well as graphitised materials as support material for the manufacture of commercially available precious metal powder catalysts. The manufacture of these carbons is described briefly, together with their most important chemical and physical properties that are tightly related to catalyst manufacture and use of such catalysts. The main industrial applications of carbon supported precious metal catalysts are also reviewed. Most of these applications make use of powder based catalysts and involve the hydrogenation of an organic substrate molecule.

Hydrogen production via the direct cracking of methane over silica-supported nickel catalysts

Abstract: We have investigated the catalytic cracking of methane as an alternative route for the production of hydrogen from natural gas. Nickel supported on silica was found to be active for this reaction producing stoichiometric amounts of hydrogen and carbon. SEM and TEM characterization of the spent catalyst indicated that carbon deposits on the catalyst in the form of hollow cylindrical filaments, with a nickel particle located on the tip of each filament. As a result, deactivation due to carbon deposition does not occur until the carbon filaments begin to interfere with each other and the silica surface, due to the spatial limitations of the pore structure of the catalyst. The deactivated catalyst can be fully regenerated by either oxidation in air or steam gasification of the deposited carbon. Additional hydrogen is produced during the steam regeneration process.

CO2 reforming of methane on Ni catalysts: Effects of the support phase and preparation technique

Abstract: The effects of the support phase and catalyst preparation methods on catalytic activity and carbon deposition were systematically investigated over nickel catalysts supported on Al2O3, SiO2 and MgO for the reforming reaction of methane with carbon dioxide. It is found that the pore structure of the support and metal-support interaction significantly affected the catalytic activity and coking resistance. Catalyst with well-developed porosity exhibited higher catalytic activity. Strong interaction between metal and the support made the catalyst more resistant to sintering and coking, thus resulting in a longer time of catalyst stability. (C) 1998 Elsevier Science B.V.

Poly(N-isopropylacrylamide) Soluble Polymer Supports in Catalysis and Synthesis

Abstract: Co- and terpolymers of N-isopropylacrylamide exhibit inverse temperature solubility in water with the polymer's lower critical solution temperature (LCST) being dependent on the polymer's microstructure and the concentration of salt in the water solvent. This solubility behavior has been used to prepare “smart” recoverable homogeneous catalysts and substrates. These catalysts' activity reversibly turns first off and then on as the temperature is first raised and then lowered due to changes in the polymer support's solubility. Such catalysts can be recovered by heating the aqueous solution or by adding brine. Catalysts prepared include both phosphine-ligated transition metal catalysts and acid catalysts. The transition metal catalysts are active in alkene hydrogenation, C−C coupling, and allylic substitution reactions. The acid catalysts are active in acetal hydrolysis. Substrates can be attached to these polymers and their activity likewise can be turned off and on by heating or cooling. Substrate activit...

Thermographic Selection of Effective Catalysts from an Encoded Polymer-Bound Library

Abstract: A general method is introduced for the rapid and simultaneous evaluation of each member of large encoded catalyst libraries for the ability to catalyze a reaction in solution. The procedure was used to select active catalysts from a library of potential polymer-bound multifunctional catalysts. From ∼7000 beads screened (3150 distinct catalysts), 23 beads were selected for catalysis of an acylation reaction. Kinetic experiments indicate that the most strongly selected beads are also the most efficient catalysts.

Reforming of methane with carbon dioxide over Ni/Al2O3 catalysts : Effect of nickel precursor

Abstract: The catalytic activities of Ni/gamma-Al2O3 catalysts prepared using different nickel precursor compounds were studied for the reaction of methane reforming with CO2. It is found that the nickel precursor employed in the catalyst preparation plays an important role. The catalyst based on nickel nitrate exhibited higher catalytic activity and stability over a 24-h test period than the other two catalysts derived from nickel chloride and nickel acetylacetonate. A comprehensive characterisation of the catalysts showed that the weak interaction between Ni particles and gamma-Al2O3 resulted in more active sites on Ni nitrate-derived Ni/gamma-Al2O3 catalyst. Coking studies showed that carbon deposition on Ni catalysts derived from inorganic precursors (nitrate and chloride) were more severe than on the organic precursor-derived catalyst. However, the Ni nitrate-derived catalyst was found to have the highest stability (or lowest deactivation rate) mainly due to the active carbon species (-C-C-) of the resulting graphitic structure and their close contact with the metal particles. In contrast, the carbon formed on Ni-AA catalyst (from Ni acetylacetonate) is dominated by inactive -CO-C- species, thus leading to a rapid accumulation of carbon in this catalyst and more severe deactivation. (C) 1998 Elsevier Science B.V.

Improved Preparation Process of Very‐Low‐Platinum‐Loading Electrodes for Polymer Electrolyte Fuel Cells

Abstract: The authors have previously reported a preparation process for the catalyst layer of polymer electrolyte fuel cells (PEFCs) using perfluorosulfonate ionomer (PFSI) colloid. In this paper they report recent improvements in this method of preparation. In the present method, a carbon-supported platinum catalyst (Pt-C) was mixed with poor solvent for PFSI, and PFSI solution was added to this mixture. The colloidal PFSI formed was immediately adsorbed on Pt-C without coagulation. As a result, the reaction area was increased, the internal resistance was decreased, and the gaseous reactants were more readily supplied to the reaction area. The authors also studied the influence of the carbon support on the microstructure of the catalyst layer. They have found that the performance of a PEFC prepared by this process with optimum carbon support and with very low platinum loading (0.1 mg/cm{sup 2}) was superior to that prepared by the previous process with conventional carbon support and with a 0.5 mg/cm{sup 2} platinum loading.

Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene: Effect of an acid component on the activity of a sulfided NiMo on alumina catalyst

Abstract: The transformation of dibenzothiophene and 4,6-dimethyldibenzothiophene was carried out in a flow reactor at 340°C under a 30 MPa hydrogen pressure A sulfided NiMo on alumina was used as reference catalyst The effect of the acidity was studied by mixing this catalyst with silica–alumina, or by using a bifunctional NiMo-Y zeolite catalyst On the sulfided NiMo on alumina catalyst, dibenzothiophene transformed mainly through direct desulfurization, yielding biphenyl This reaction was much slower in the case of 4,6-dimethyldibenzothiophene, which renders the molecule less reactive The addition of an acidic function to the sulfide catalyst did not modify the reactivity of dibenzothiophene while it strongly increased that of 4,6-dimethyldibenzothiophene This is attributed to the isomerization of 4,6-dimethyldibenzothiophene into 3,6-dimethyldibenzothiophene, which is more reactive than 4,6-dimethyldibenzothiophene In the presence of an acidic component, cracking of the desulfurized molecules can also be observed

High surface area silicon carbide as catalyst support characterization and stability

Abstract: High surface area silicon carbide (SiC) of 30 m 2 /g has been synthesized by the catalytic conversion of activated carbon. The stability of this SiC in aqueous hydrogen fluoride and a boiling nitric acid solution is shown to be excellent. No corrosion is encountered by treatment with boiling HNO 3 , HF treatment causes the dissolution of the silica surface layer present on the SiC while the SiC remains intact. Oxidation in air at elevated temperatures has been analyzed by thermal gravimetric analysis, diffuse reflectance infrared spectroscopy, nitrogen adsorption, and X-ray diffraction. The thermal stability in non-oxidizing environments is shown to be excellent; no significant sintering has been observed after ageing in nitrogen for 4 h at 1273 K. The presence of 2 v% steam at 1273 K results in partial SiC oxidation into SiO 2 and considerable sintering. Air oxidation at 1273 K of pure SiC, SiC loaded with 5 wt.% nickel, and HNO 3 treated SiC is shown to cause substantial SiC conversion, viz. 60% to 70% after 10 h. Air oxidation at 1080 K will result in complete conversion in about 100 days. This rate of oxidation agrees with reports on the oxidation of non-porous Acheson SiC and SiC coatings formed by Chemical Vapour Deposition. It is concluded that at high surface area SiC cannot be used as a catalyst support in processes operating in oxidizing environments and temperatures above 1073 K. SiC based catalysts are very well suited for (1) high-temperature gas-phase reactions operating in the absence of oxidizing constituents (O 2 or H 2 O) and (2) strong acidic liquid-phase processes.

Cobalt based fisher-tropsch catalyst

Abstract: A process for the preparation of a cobalt-containing catalyst or catalyst precursor, comprising (a) mixing (1) titania or a titania precursor, (2) a liquid, and (3) a cobalt compound, which is at least partially insoluble in the amount of liquid used, to form a mixture, (b) shaping and drying of the mixture thus-obtained, and (c) calcination of the composition thus-obtained. A catalyst or catalyst precursor obtainable by the process as defined, and a process for the preparation of hydrocarbons comprising contacting a mixture of carbon monoxide and hydrogen with the catalyst as defined.

Polyolefin Spheres from Metallocenes Supported on Noninteracting Polystyrene

Abstract: To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of alpha-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 degreesC affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.

Co-methanation of carbon monoxide and carbon dioxide on supported nickel and cobalt catalysts prepared from amorphous alloys

Abstract: The activity and durability of the catalysts prepared by the oxidation–reduction treatment of amorphous Co-15 at% Zr, Ni-40 at% Zr and Ni-30 at% Zr-10 at% Sm alloys have been investigated for simultaneous methanation of carbon monoxide and carbon dioxide. It has been found that the Ni–30Zr–10Sm catalyst shows the highest activity among the catalysts examined, and the activity of the Co–15Zr catalyst is lower than those of the nickel-based catalysts, in agreement with the activity for the solo methanation of carbon dioxide. On all the catalysts, carbon monoxide reacts preferentially with hydrogen, and is completely converted into methane at and above 523 K. The remaining hydrogen further reacts with carbon dioxide to form methane. The methanation rate in the H 2 –CO–CO 2 mixed gas is higher than that in H 2 –CO mixed gas without CO 2 . This is probably related to the prevention of the formation of surface carbon by the disproportionation reaction of carbon monoxide due to the presence of carbon dioxide. The activity of the Ni–40Zr catalyst at 573 K gradually decreases with reaction time. It has been found that tetragonal ZrO 2 , the presence of which is responsible for the high activity, is transformed to thermodynamically more stable monoclinic ZrO 2 during the catalytic reaction. In contrast to the Ni–40Zr catalyst, the Ni–30Zr–10Sm catalyst sustains the initial high activity, and no structural change is observed during the durability test regardless of the presence of a small amount of hydrogen sulfide.

Process for upgrading a hydrocarbon oil

Abstract: A catalyst assisted upgrading process for treating a hydrocarbon oil feed to reduce total acid number (TAN) and increase API gravity is provided herein which employs a hydroprocessing catalyst based on a catalyst support, e.g., alumina. The process includes blending the supported hydroprocessing catalyst with the hydrocarbon oil feed to form a slurry which is then treated with hydrogen at moderate temperature and pressure in, for example, a tubular reactor. Deposit formation is thus minimized or avoided.

Mixed catalyst system

Abstract: It has been found that the use of at least one unsupported metallocene polymerization catalyst with at least one supported metallocene polymerization catalyst in the polymerization of olefins allows for better control of the polymerization, especially gas phase polymerization. Such a system takes advantage of the high activity of the unsupported catalyst and the stability of a supported catalyst. Additionally, the relative timing of the addition of the supported and unsupported catalysts to a reaction system can be used to control a continuous polymerization reaction by stabilizing the reactor bed with the supported catalyst prior to addition of the unsupported catalyst.

Conversion of ethane into benzene on Mo2C/ZSM-5 catalyst

Abstract: The reaction of ethane on unsupported and supported molybdenum compounds has been investigated at 773–973 K. ZSM-5 was used as support. Reaction products were analyzed using gas chromatography. Changes in the composition of catalyst samples were followed by X-ray photoelectron spectroscopy. Unsupported MoO3 is partially reduced with ethane above 800 K to give H2O and CO2. The formation of H2, C2H4 and CH4 was also observed. Mo-free ZSM-5 exhibited relatively high activity towards dehydrogenation, hydrogenolysis and aromatization of ethane above 773 K. Deposition of MoO3 on ZSM-5 significantly enhanced the conversion of ethane and also the selectivity of benzene production. Alteration of the catalytic behaviour of MoO3/ZSM-5 in time on-stream at 773–973 K was attributed to the reaction of MoO3, to carbon deposition and to the formation of Mo2C. Unsupported Mo2C catalyzed the dehydrogenation of ethane without producing benzene. In contrast, Mo2C/ZSM-5 was found to be an effective catalyst in the aromatization of ethane. At 973 K the conversion of ethane was ∼67% and the selectivity to benzene formation 31%.