Effect of Palladium Size on its Chemical Activity
S. Y. Huang and C. T. Yeh
National Tsing-Hua University, TW
Keywords: hydrogen, potential energy surface , palladium
Palladium crystallites with size down to d < 1 nm or were successfully dispersed on silica support and characterized with TEM. A process of hydrogen absorption into the dispersed crystallites were studied by a simultaneous technique of volumetry and calorimetry. Measured hydrogen uptake isotherms revealed that the absorption was proceeded through three distinct stages, i.e., chemisorption on surface, penetration to sublayers and absorption into crystallite bulk. However, the uptake ratio of chemisorption to absorption and the heat of hydrogen chemisorption, obtained from the volumetry the calorimetry respectively, varied significantly with the diameter (d) of palladium crystallites at d < 5 nm. A similar size effect has also been found on enthalpies in the hydrogen absorption and the oxygen chemisorption. Adsorption and desorption of gases are essential steps in technologies of sensor, electrochemistry and catalysis. Variation in the size of nanoparticles should affect significantly their application. In this presentation, a reaction of NO decomposition into nitrogen and oxygen over palladium surface will be used as an example to illustrate the extent of size effect on catalysis.
NSTI Nanotech 2003 Conference Technical Program Abstract