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

Abstract

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...

Hydrogen isotopic exchange between D2 and H2O on alumina prepared by sputtering

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“…Coefficients in the denominator are equivalent to the adsorption equilibrium constants for reactions [ I ] and [5]. The equilibrium equation can be expressed as follows (29), c a fa…”

“…The second component promotes the dispersion of platinum and prevents sintering during heat treatment, realizing a large effective surface area. In addition, it often enhances the catalytic activity (5)(6)(7). Thus, the apparent catalytic activity of supported catalysts varies in both the physical and the chemical sense.…”

Preparation of Tritium‐Labeled Compounds by Chemical Synthesis

“…The latter may be illustrated by the synthesis of [4,4,5, H]TLCK (41) (Figure 4.15). Complete reduction to the saturated compound is easily accomplished over palladium or platinum catalysts.…”

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