The Influence of the Substrate on Hydrogen–Water Deuterium Exchange over Carbon Supported Platinum

Sagert, Norman H.; Pouteau, Rita Mary Louise

doi:10.1139/v72-583

Cited by 23 publications

(23 citation statements)

References 13 publications

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“…The mechanism is summarized below and involves adsorption of hydrogen and water kapor on different sites I and 11. If reaction 7 is taken to be rate limiting, the following rate expression is obtained (1,13):…”

Section: Discussionmentioning

confidence: 99%

“…Rates were measured in a flow system at a total pressure of 101 kN rn-' using techniques previously described (1,2). The HD concentrations were measured with a Consolidated 21-621 mass spectrometer fitted with a cont~nuous inlet.…”

Section: Methodsmentioning

confidence: 99%

“…the reaction is of interest as a method of producing heavy water commercially. We previously noted that the reaction was faster and proceeded with a lower activation energy over platinum supported on highly graphitized carbon than over unsupported platinum (1) or over platinum supported on silica (5). This led us to propose that graphite donated electrons to the platinum, giving rise to a platinum-hydrogen bond polarized in the sense Pts'-H".…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen–Water Deuterium Exchange over Unsupported Group VIII Noble Metals

Sagert¹,

Pouteau²

1974

Can. J. Chem.

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NORMAN H. SAGERT and RITA M. L. POUTEAU. Can. J. Chem. 52,2960Chem. 52, (1974. Specific activities of unsupported powders of all six Group VIII noble metals have been determined for hydrogen -water deuterium isotope exchange. The metal surface areas, which are required to calculate the specific activities were measured by hydrogen chemisorption and were checked by electron microscopy. Specific activities were measured as a function of temperature in the range 353 to 573 K and also as a function of the partial pressure of hydrogen and water a t suitable temperatures and over a tenfold range of partial pressures.The variation in the specific activities was Pd i Ir 5 Ru i R h < 0 s i Pt, and these specific activities varied over a range of about 1000. The observed orders with respect to hydrogen and water are shown to be consistent with a mechanism in which chemisorbed hydrogen atoms exchange with physically adsorbed water.From the orders and the apparent activation energies, the chemical activation energies (Eo) were calculated. These varied randomly within the range 61 F 6 kJ mol-' for all the metals studied. Previously we showed that there was a correlation of Eo with the work function of the metal when metals were supported on a highly graphitized carbon black, and suggested that electron donation from the carbon to the metal was responsible for the correlation. This suggestion is supported by the present results which show that Eo is relatively constant for all six metals in the absence of a support. 52,2960 (1974).On a determine les activites specifiques des six metaux nobles du groupe VIII pour l'tchange de deuterium hydrogene -eau. La superficie de la surface metallique,qui est necessaire pour calculer les activites specifiques a ete evaluee par chemisorption de I'hydrogene et verifiee par microscopie electronique. On a mesure les activites specifiques en fonction de la temperature dans l'intervalle de 353 a 573 K et aussi en fonction de la pression partielle d'hydragene et d'eau aux ten~peratures appropriees et sous dix intervalles de pressions partielles.Les activites specifiques varient dans I'ordre Pd i Ir 5 Ru < Rh i 0 s i Pt, dans un intervalle environ de 1000. Les ordres que Ilon observe par rapport a l'hydrogene et I'eau son1 en accord avec le mecanisme dans lequel des atomes d'hydrogenes chemisorbes s'echangent avec I'eau adsorbee de maniere physique.On

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hydrogen–Water Deuterium Exchange over Unsupported Group VIII Noble Metals

Sagert¹,

Pouteau²

1974

Can. J. Chem.

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“…Rates were measured in a flow system at atmospheric pressure, as previously described (4,5). The H D concentrations were measured either by gas chromatography or with a Consolidated 21-621 mass spectrometer fitted with a continuous inlet.…”

Section: Appam~us Nrzd Proced~rrementioning

confidence: 99%

“…Hydrogen-water deuterium isotope exchange is a reaction which does not involve such complications (3,4). Moreover it is a srerically simple o r "facile" reaction (5), s o that in studying it over a series of metals the electronic, or chemical, effects should predominate over geometric effects.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

Sagert¹,

Pouteau²

1973

Can. J. Chem.

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Specific activities of Group VIII noble metals supported on Graphon have been determined for hydrogen-water deuterium exchange. Metal surface areas, which are required to calculate specific activities, were measured by hydrogen chemisorption, and by reaction of hydrogen with chemisorbed oxygen. For the second triad metals, ruthenium, rhodium, and palladium, and in the temperature range 140 to 225 "C, the variation of activity was R u < R h > Pd. For the third triad metals, osmium, iridium, and platinum, the variation of activities was O s < I r < Pt in the same range of temperature. Apparent activation energies were measured over this temperature range, and orders of reaction with respect to hydrogen and water were measured at 160 "C (200 "C for Pt). From these data, activation energies for the surface exchange reaction were calculated. In the second triad the activation energies decrease slightly with increasing atomic number, but in the third triad they decrease quite markedly with increasing atomic number. A good correlation was obtained between the activation energy for surface exchange and the thermionic work function of the metal. This supports our earlier suggestion that Graphon is able to donate electrons to the metal and thus lower the activation energy for the surface exchange.L'activite specifique de metaux nobles du groupe VIII fixes sur Graphon a it6 determinee pour I'Cchange de deuterium H,-HDO. La superficie de la surface mitallique, qui est necessaire lors du calcul des activites specifiques, a kt6 Cvaluee a I'aide de la chemisorption de I'hydrogene ainsi qu'a I'aide d e la reaction de I'hydrogene avec de I'oxygene chemisorbe. Pour la seconde triade de metaux, ruthenium, rhodium et palladium, et dans I'intervalle de temperatures allant de 140 a 225 "C, la variation d'activite a ete dans I'ordre Ru < Rh > Pd. Pour la troisieme triade de metaux, osmium, iridium et platine, la variation d'activite a e t t dans I'ordre 0 s < Ir < Pt dans le m&me intervalle de temperatures. Les Cnergies apparentes d'activation ont etC mesurees pour cet intervalle de temperatures alors que I'ordre des reactions par rapport a I'hydrogene et a l'eau a ete determine a 160 "C (200 "C pour le Pt). A partir d e ces donnees, on a calcule pour les reactions d'echange se faisant en surface les energies d'activation. Dans la seconde tr~ade, les energies d'activation diminuent lkgerement selon I'ordre croissant des nurneros atomiques, alors que dans la troisieme triade elles diminuent selon I'ordre croissant des numeros atomiques d'une f a~o n assez marquee. Une bonne correlation a ete obtenue entre I'energie d'activation pour I'Cchange en surface et la fonction du travail thermionique du metal. Ce fait est en accord avec nos suggestions antirieurs voulant que le Graphon est capable de donner des electrons au metal et ainsi diminuer I'Cnergie d'activation necessaire a l'echange en surface.[Traduit par le journal] Can. J. Chem., 51,4031 (1973) Introduction Group VIII metals have been shown to be good catalysts for most hydrogen...

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Kinetics of iodine poisoning of hydrophobic Pt/SDBC catalyst for hydrogen isotopic exchange reaction

Wei¹,

Shimizu²,

Takeshita³

et al. 1997

Can J Chem Eng

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Changes with time in the isotopic exchange reaction rate between H, and HDO(v) over a hydrophobic PtiSDBC (styrene-divinylbenzene copolymer) catalyst induced by iodine have been studied experimentally. The addition of a trace amount of I2 to the reactor caused a remarkable decrease in the activity of the catalyst. The measurement results by means of the gas chromatographic pulse technique show that the H, adsorption onto the catalyst surface was strongly inhibited by iodine. A kinetic model for the poisoning was developed in terms of the competitive adsorption of I2 with H, onto the catalytic active site. The experimental results were explained reasonably by the proposed kinetic model based on the site balance by assuming that I2 adsorbs non-dissociatively on the active site. The poisoning could be prevented by the conversion of I . to Ior IO; through redox reactions.On a etudie experimentalement les changements dans le temps de la vitesse de reaction d'echange isotopique entre H2 et HDO(v) sur un catalyseur hydrophobe Pt/SDBC (copolymere styrene-divinylbenzene) induit par de I'iode. L'ajout de traces de I, au reacteur entraine une diminution notable de I'activite du catalyseur. Les mesures effectuees par la technique de chromatographie en phase gazeuse par impulsions. montrent que I'adsorption de H2 sur la surface du catalyseur est fortement inhibee par I'iode. Un modele cinetique d'empoisonnement a ete mis au point en utilisant I'adsorption competitive de 1: avec H, sur le site catalytique actif. Les resultats experimentaux ont ete expliques raisonnablement par le modele cinetique propose base sur le bilan des sites en supposant que I2 s'adsorbe de fagon non dissociative sur le site actif. L'empoisonnement peut etre evite par la conversion de I2 en Iou lo; par les reactions d'oxydo-reduction.

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The Influence of the Substrate on Hydrogen–Water Deuterium Exchange over Carbon Supported Platinum

Cited by 23 publications

References 13 publications

Hydrogen–Water Deuterium Exchange over Unsupported Group VIII Noble Metals

Hydrogen–Water Deuterium Exchange over Unsupported Group VIII Noble Metals

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

Kinetics of iodine poisoning of hydrophobic Pt/SDBC catalyst for hydrogen isotopic exchange reaction

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