Tungsten and tungsten carbide supported on activated carbon:: Surface structures and performance for ethylene hydrogenation

Tungsten catalysts supported on an activated carbon were prepared, with different metal loading, by using either ammonium tungstate or tungsten hexacarbonyl as metal precursor compounds. The catalysts so prepared were heat treated in H-2 flow at 748 and 973 K or in He flow at 1223 K. The heat-treated catalysts were characterized by N-2 adsorption at 77 K and mercury porosimetry, to determine their surface area and porosity, and by XPS and XRD, to evaluate the chemical state and dispersion of the active phase. These catalysts were tested in the hydrogenation reaction of ethene. The treatments in H-2 yielded an active phase composed of metallic tungsten and tungsten trioxide, whereas the treatment in He generated a mixture of metallic tungsten, tungsten carbide, and tungsten trioxide. The catalysts containing tungsten carbide were the most active in the hydrogenation of ethene, even at a temperature as low as 273 K, although their rate of deactivation was dependent on reaction temperature; the lower the reaction temperature, the higher the rate of deactivation.