W-modified Ni/Al2O3 catalysts for the dry reforming of methane: Effect of W loading

W-modified Ni/Al2O3 catalysts were investigated for the dry reforming of methane. xW-Ni/Al2O3 catalysts (10 wt% Ni and tungsten loading in the range of x=0-26.2 wt% W) were synthesized by wet co-impregnation. Textural and structural characteristics were studied by N-2 adsorption- desorption, XRD, UV-vis DRS, Raman, TPR, NH3-TPD and HR-TEM. Catalytic behaviour was evaluated using a feed of 50% CH4 and 50% CO2, at 973 K and atmospheric pressure. Qualitative and quantitative analyses of the amount and the structure of carbonaceous deposits on the used catalysts were performed by TPH, TPO, XRD and HR-TEM. Modification with tungsten loading up to 11.9 wt% causes a slight decrease in activity but results in significant reduction of carbonaceous deposits. As tungsten loading increases further, catalytic activity decreases significantly. The suppression of carbon formation was attributed to the double role of tungsten: a) Ni-W alloys, formed during reduction, hinder carbon diffusion in their lattice; b) carbon remaining at the surface is removed through a carbon formation-gasification mechanism involving tungsten carbides. The catalyst doped with 11.9 wt% W exhibited catalytic performance comparable to that of the undoped Ni/gamma-Al2O3 catalyst but forms 76% less carbon.