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 dif ferent metal loading, by using either ammonium tungstate or tungsten hexaca rbonyl as metal precursor compounds. The catalysts so prepared were heat tr eated in H-2 flow at 748 and 973 K or in He flow at 1223 K. The heat-treate d catalysts were characterized by N-2 adsorption at 77 K and mercury porosi metry, to determine their surface area and porosity, and by XPS and XRD, to evaluate the chemical state and dispersion of the active phase. These cata lysts were tested in the hydrogenation reaction of ethene. The treatments i n H-2 yielded an active phase composed of metallic tungsten and tungsten tr ioxide, whereas the treatment in He generated a mixture of metallic tungste n, tungsten carbide, and tungsten trioxide. The catalysts containing tungst en carbide were the most active in the hydrogenation of ethene, even at a t emperature as low as 273 K, although their rate of deactivation was depende nt on reaction temperature; the lower the reaction temperature, the higher the rate of deactivation.