SELECTIVE CHEMISORPTION OF CARBON-MONOXIDE AND HYDROGEN OVER SUPPORTED MOLYBDENUM CARBIDE CATALYSTS

In order to establish procedures to determine the number of exposed metal sites and the particle size of molybdenum carbide catalysts by selective chemisorption of CO and H-2, alumina supported molybdenum and its carbides were studied by CO and H-2 chemisorption at different temperatures, TPD, XRD, and TEM. Carbon monoxide appeared to chemisorb molecularly on molybdenum carbide at 196 K, yet substantial amounts of chemisorbed CO desorbed upon heating to room temperature. Hydrogen chemisorption was an activated process and required elevated temperatures. Hence, CO chemisorption at 196 K and H-2 chemisorption as the sample is cooled from 620 K to room temperature provided the number of exposed metal sites and the particle sizes, which are consistent with each other and with TEM results as well.