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173 results on '"Seshan, Kulathuiyer"'

156. The effect of addition of a third component on the behaviour of the lithium doped magnesium catalysts for the oxidative dehydrogenation of ethane

Author

Swaan, H.M., Toebes, A., Seshan, Kulathuiyer, van Ommen, J.G., Ross, J.R.H., Catalytic Processes and Materials, and Faculty of Science and Technology

Subjects
Ethylene, METIS-105439, Magnesium, Sodium, Inorganic chemistry, chemistry.chemical_element, IR-9990, General Chemistry, Catalysis, chemistry.chemical_compound, chemistry, Dehydrogenation, Selectivity, Cobalt, Carbon monoxide
Abstract

The oxidative dehydrogenation of ethane was studied with the use of promoted Li/MgO catalysts at temperatures of 600¿650°C. The addition of known promoters, cobalt and tin, gave a slight Increase In activity but a strong decrease in selectivity to ethylene under the conditions used. The addition of sodium improved the selectivity to ethylene and suppressed the formation of carbon monoxide. Using a feed of 12 vol% ethane and 6 vol% oxygen, the U/Na/MgO catalyst with 3.2wt% sodium showed a selectivity of 86 % to ethylene at 38 % conversion of ethane; the Li/MgO catalyst showed a selectivity of 80 % at similar conversions Thermal Investigations of the Li/Na/MgO catalyst showed that an eutectic melt of LINaCO3 is formed at 490°C; the existence of this molten phase is probably the cause of the Increased selectivity.

Published
1992

166. Stable and Efficient Pt-Re/TiO2 catalysts for Water-Gas-Shift: On the Effect of Rhenium.

Author

Azzam, Khalid G., Babich, Igor V., Seshan, Kulathuiyer, Mojet, Barbara L., and Lefferts, Leon

Subjects
PLATINUM catalysts, TITANIUM dioxide, RHENIUM catalysts, WATER gas shift reactions, INTERMEDIATES (Chemistry), ADSORPTION (Chemistry), TEMPERATURE effect, CARBON monoxide
Abstract

The catalytic performance of Pt-Re/TiO2 catalysts, that is, activity and stability, in single-stage water gas shift reactions was investigated by studying the influence of preparation strategies, Pt/Re molar ratios, and metals contents. Results show that sequential impregnation of Re precursor prior to Pt precursor without intermediate pretreatment is the optimum preparation strategy. The Pt/Re ratio of unity with 0.5 wt. % Pt content resulted in the most significant effect on activity and stability. In situ characterizing of both monometallic and the optimal bimetallic Pt-Re catalysts by means of CO chemisorption, H2 temperature programmed reduction, and FTIR spectroscopy under the reaction conditions provided evidence that Re increases the activity by enhancing the activation of water. No evidence was found for any direct influence of Re on the properties of Pt in the catalyst under the reaction conditions. [ABSTRACT FROM AUTHOR]

Published
2013
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167. Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming.

Author

Nagaoka, Katsutoshi, Seshan, Kulathuiyer, Takanabe, Kazuhiro, and Aika, Ken-ichi

Subjects
CATALYSTS, COAL carbonization, HIGH pressure (Science), HIGH pressure (Technology), CHEMICAL inhibitors, INDUSTRIAL chemistry
Abstract

CH4/CO2 reforming over Pt/ZrO2, Pt/CeO2 and Pt/ZrO2 with CeO2 was investigated at 2 MPa. Pt/ZrO2, which shows stable activity under 0.1 MPa, and Pt/CeO2 showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO2 with CeO2 prepared by different impregnation order (co-impregnation of Pt and CeO2 on ZrO2, and consecutive impregnation of Pt and CeO2 on ZrO2). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO2 and Pt/CeO2). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H2 reduction, and the CH4/CO2 reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt-Ce)/ZrO2 prepared by impregnation of CeO2 on Pt/ZrO2 and the catalyst showed highest stability. [ABSTRACT FROM AUTHOR]

Published
2005
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168. An in situIR study of the NOxadsorptionreduction mechanism on modified Y zeolites

Author

Sedlmair, Christian, Gil, Barbara, Seshan, Kulathuiyer, Jentys, Andreas, and Lercher, Johannes A.

Abstract

The surface species formed during adsorption of NO, NO  O2and NO2on sodium and barium exchanged Y zeolites have been investigated by in situIR spectroscopy. Ionically bound nitrates and nitrites on the exchanged metal cation sites are the main species formed during adsorption of NO and NO2. Extra framework alumina was identified as additional sorption site forming small concentrations of bridging, chelating and monodentate nitrates. N2O4and NOwere found to be reaction intermediates during the NOxadsorption process. The direct oxidation of NO2with reactive oxygen from the zeolite surface is facilitated by the formation of nitrates viathe disproportionation reaction of N2O4to NOand NO3−. NOwas found to act as precursor for the creation of nitrites. Decomposition of the nitrate species occurs between 150 and 450 °C. During the temperature increase less stable nitritenitrate species are transformed into Ba-nitrates showing the highest thermal stability. The stability of surface nitratesnitrites was found to be lower, if NO instead of NO2is present in the feed during temperature increase. For the interaction of surface NOxspecies with propene two pathways are proposed. At low temperatures, NOwas identified as the active NOxsurface species reacting with propene to nitriles. At higher temperatures the reduction of surface nitratesnitrites occurred viaorganic nitronitrito species, carboxylic species and isocyanates.

Published
2003
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169. Carbon Deposition during Carbon Dioxide Reforming of Methane—Comparison between Pt/Al2O3and Pt/ZrO2

Author

Nagaoka, Katsutoshi, Seshan, Kulathuiyer, Aika, Ken-ichi, and Lercher, Johannes A

Abstract

The relation between coke formation and the deactivation of supported Pt catalysts during CO2reforming of methane at temperatures above 1070 K such as used in the commercial process was studied. Temperature-programmed oxidation and temperature-programmed reaction with CO2were applied to Pt catalysts (Pt/Al2O3and Pt/ZrO2) which were exposed to CH4/CO2(reforming reaction conditions) or CH4/He (facile coke formation) to identify the carbon species. The activity decrease for Pt/Al2O3was rather slow and minor at high temperature (≥1070 K), while it was fast and almost complete during a comparative experiment at low temperature (875 K). Coke deposited on the supported Pt particles was oxidized by CO2, but coke on the Al2O3support was not removed at 1070 K. At this temperature the decay in activity with time on stream corresponded solely to the amount of coke accumulated on Pt particles. This indicates the main reaction between CO2and CH4on all Pt atoms without significant participation of the support. The activity is concluded to decrease gradually due to coverage of Pt by coke induced by CH4decomposition (initial phase of deactivation observed at high temperature). After a while only the perimeter of Pt particles remains as site of activity. There, the activity is speculated to be stable because of the higher reactivity of CO2at the metal–support boundary. Gradually, the coke on the support (Al2O3) increases to an extent that it blocks the reaction also at that location. In contrast to the situation with Pt/Al2O3, coke was not observed on Pt/ZrO2even after exposure to reforming gas (CH4/CO2) for 12 h. The combination of three factors is concluded to cause the high catalytic stability of Pt/ZrO2in CO2/methane reforming: (i) coke on Pt (supported on ZrO2) is more reactive toward CO2than coke on Pt (supported on Al2O3) under reforming reaction conditions/ (ii) methane decomposition is slower on Pt/ZrO2than on Pt/Al2O3; and (iii) coke is hardly formed on the ZrO2support.

Published
2001
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170. Synthesis of carbon nanofibers as support layer for metal catalysts in a microreactor for three-phase reactions

Author

Thakur, D.B., Tiggelaar, Roald M., Seshan, Kulathuiyer, Gardeniers, Johannes G.E., Lefferts, Leonardus, D'Arrigo, Giuseppe, Vincenzini, Pietro, Catalytic Processes and Materials, and Mesoscale Chemical Systems

Subjects
Materials science, Carbon nanofiber, Catalyst support, Tantalum, chemistry.chemical_element, Substrate (chemistry), respiratory system, equipment and supplies, Nickel, IR-94274, METIS-250603, Carbon nanofibers, chemistry, Chemical engineering, Flat substrates, Underlayers, Composite material, Microreactor, Layer (electronics), Nickel thin film, Titanium
Abstract

Carbon Nanofibers (CNF) layers were synthesized nickel-based thin-films on flat fused silica substrates. CNF synthesis was performed via thermal catalytic chemical vapor deposition of ethylene using nickel as metal catalyst. Different underlayer metal thin films, viz. titanium, tantalum and titanium-tungsten were tested in order to obtain stable and well-attached CNF films on fused silica substrates. It is found in case of titanium CNFs are formed on the nickel, but due to severe Ni/Ti inderdiffusion the titanium film looses its adhesive function, as a consequence of which the formed CNF film detaches from the substrate. The use of tantalum or titanium-tungsten as adhesion layer resulted in stable and well-adhered CNF films on fused silica substrates, of which the morphology can be controlled by the growth time.

171. Oxidative dehydrogenation of propane over niobia supported vanadium oxide catalysts

Author

Watling, T.C., Deo, G., Seshan, Kulathuiyer, Wachs, I.E., Lercher, J.A., Catalytic Processes and Materials, and Faculty of Science and Technology

Subjects
Alkane, chemistry.chemical_classification, Inorganic chemistry, Vanadium, chemistry.chemical_element, IR-10173, General Chemistry, Photochemistry, Heterogeneous catalysis, Catalysis, Vanadium oxide, Propene, chemistry.chemical_compound, chemistry, Propane, Dehydrogenation, METIS-105530
Abstract

Oxidative dehydrogenation (ODH) of propane is examined over a series of catalysts, which include Nb2O5 supported monolayer V2O5 catalysts, bulk vanadia-niobia with different vanadium oxide loadings and prepared by four different methods, V2O5and Nb2O5. The intrinsic activity (TOF) of the samples studied indicates that vanadium containing active sites are indispensable for catalytic oxidative dehydrogenation of propane. Variations in the chemical environment of the vanadium ion do not cause significant changes in activity per site and, hence, all samples show similar TOF when the rates are normalised to the concentration of V on the surface. Selectivity to propene on the other hand strongly depends on the nature of the catalyst because readsorption and interaction of propene with the acid sites leads to total oxidation. Optimization of the weak sorption of propene is, therefore, concluded to be the key factor for the design of selective oxidative dehydrogenation catalysts.

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