CHARACTERIZATION OF TUNGSTEN CARBIDE POWDER BY CHEMISORPTION

In order to determine the number of exposed catalytic sites of unsuppo rted tungsten carbide catalysts - with WC structure - chemisorption of H-2, O2, CO and N2 was studied. Samples included commercially availab le carbides, but also carbides which were synthetized in situ from WO3 which was directly carburized at atmospheric pressure and under flow conditions by a mixture of methane in hydrogen at 1150 K. Special care has been exercised to establish a procedure leading to uncontamined c arbide surfaces. When chemisorption is performed at 298 K, H, O, N and CO coverages are 0.57, 1.3, 0.11 and 0.65 on all carbide powders (cov erage 1 = one monolayer = 10(15) sites.cm-2). But H-2 chemisorption is partly an activated process and a coverage as high as 1.1 can be obta ined when H-2 adsorption takes places on samples being cooled from 900 K to room temperature.