The Specific Activity of Silica Supported Platinum for the Catalysis of Hydrogen – Water Deuterium Exchange

Abstract

Some rate data are reported for deuterium exchange between water and hydrogen using a series of platinum-silica catalysts. Three different methods of preparing catalysts were used to give different series of metal particle sizes. Within each series, the particle size was increased by sintering batches in air, at temperatures up to 700 "C. These methods produced platinum particles ranging from 5 to 250 A in diameter. Metal surface areas and particle sizes were measured by hydrogen chemisorption, X-ray diffraction, and electron microscopy.The specific rates, i.e., rates per unit surface area of platinum varied by a factor of three within each series, reaching a maximum for sintering temperatures of about 500 "C. These maximum rates, measured at 127 "C with a water-to-hydrogen ratio of 0.31, varied from 1.9 x lo-' to 5 x lo-' mol D, cm-2 s-'. Thus no effect of particle size on rate was observed, and the differences noted are ascribed to other effects of the methods of preparing the catalysts.Certaines donnees de vitesse sont report& pour 1'Cchange du deuterium entre l'eau et I'hydrogene lorsqu'on utilise une serie de catalyseurs platine-siiice. Trois mkthodes differentes de preparation des catalyseurs ont permis d'obtenir differentes series de taille de particule metallique. Dans chaque serie, la taille de la particule a Bte augmentee par frittage dans I'air a des temperatures supkrieures a 700 "C. Ces methodes ont donne des particules de platine dont la gamme d b diametres varie de 5 250 A. Les aires de surfaces metalliques et les tailles des particules sont mesurees par chimisorption de l'hydrogene, par diffraction aux rayons-X et par microscopie Blectronique.Les vitesses specifiques, c'est-a-dire les vitesses par unite de surface du platine, varient avec un facteur de trois dans chacune des series, atteignant un maximum pour des tempkratures de frittage de l'ordre de 500 "C. Ces vitesses maximales mesurees a 127 "C avec un rapport eau-hydrogene de 0.31, varient de 1.9 x a 5 x lo-' mol D2 ~m -~ s-l. Par contre, aucun effet de la taille des particules n'a kt6 observee et les differences notees sont assignees aux autres effets des methodes de preparation des catalyseurs.

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

“…4317. size effect for the catalysis of hydrogen-water deuterium exchange over silica supported platinum (6). The present work is an examination of the role of the support on the same reaction.…”

“…Rate measurements were carried out in a flow system at atmospheric pressure as previously described (6). To investigate the rates as a function of hydrogen pressure, provision was made for mixing argon with the hydrogen before the combined stream was saturated with water containing 4% D,O.…”

“…Purified argon did not interfere with the gas chromatographic determination of HD. The catalyst reduction procedures were identical to those used earlier (6) except that the final reduction was done at 300 "C.…”

“…If the amount of D,O is kept low, the only product is HD. This simplifies the kinetics and makes the reaction easy to follow by measuring HD (6,7). The reaction is also of interest as a method of producing heavy water commercially.…”

“…Thus it was necessary to study the kinetics in somewhat more detail than in our previous work on silica supported platinum (6 For personal use only.…”