DISPERSION AND STRUCTURE OF PLATINUM-IRIDIUM CATALYSTS

A series of supported platinum-iridium catalysts was investigated by hydrogen chemisorption and X-ray diffraction. The catalysts all contained equal amounts of platinum and iridium by weight. Chemisorption measurements were made on both silica and alumina supported catalysts containing amounts of platinum plus iridium ranging from 0.6 to 20 wt%. For given contents of platinum and iridium, hydrogen chemisorption was higher on catalysts supported on alumina, indicating a higher degree of metal dispersion on alumina than on silica. X-ray diffraction measurements were limited to silica supported samples with platinum plus iridium contents ranging from 5 to 20 wt%. The presence of platinum-iridium bimetallic clusters is evident from the diffraction patterns, which exhibit diffraction lines at positions approximately midway between the positions of the corresponding lines for platinum and iridium metals. X-ray diffraction studies on alumina supported samples are complicated by interference from the diffraction pattern of the alumina. © 1979.