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 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 Å 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 × 10−8 to 5 × 10−8 mol D2 cm−2 s−1. 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.