Pressure dilution, a new method to prepare a stable Ni/fumed silica catalyst for the dry reforming of methane

摘要

A novel method of catalyst preparation, using pressure dilution, which increased the dispersion and stability of a Ni/fumed SiO(2 )catalyst is described. We first studied the effect of carbon formation on the activity and stability of Ni/fumed SiO2 catalysts at different times on stream (TOS) during the dry reforming of methane (DRM). The catalysts were characterized by SEM/TEM and BET, XRD, XPS, TGA/DSC, and CO chemisorption. Catalysts prepared by impregnation of Ni(NO3)(2)center dot 6H(2)O onto fumed SiO2, were subjected to various pretreatments which yielded high initial activities at 600 degrees C. The activation energy was measured to be 91 kJ/mol and the initial rate was of 8.5 [mol of CH4 /g(Ni )h] comparable with Pt-Ni alloy catalysts. Depending on the pretreatment, however, the catalysts deactivated at different rates due to carbon formation. The carbon structure was studied by SEM/ TEM and its amount measured by a carbon analyzer. We found that carbon accumulates mostly in the form of carbon nanotubes (C-NT) with Ni crystallites at the top, where the reaction takes place without affecting the activity during first hours of TOS. We also found formation of clumps of entangled C-NT with Ni crystallites encapsulated by the entangled C-NT, leading to loss of active area and deactivation.