Solid Acid Catalytic Dimerization of Ethylene to Butenes

A series of supported WO₃/ZrO_x(OH)_4-2x (abbreviated as WO_x/ZrOH) and Ni-WO₃/ZrO_x(OH)_4-2x (abbreviated as Ni-WO_x/ZrOH) catalysts was synthesized and examined for ethylene dimerization to isobutene. The catalysts were synthesized by standard aqueous impregnation of ammonium metatungstate onto an amorphous ZrO_x(OH)_4-2x support, followed by impregnating Ni(NO₃)₂●6H₂O onto the 10.1-wt%WO_x/ZrOH catalyst. The catalysts were dried and calcined in air at 673-1073K. Characterization with in situ Raman spectroscopy revealed the presence of highly dispersed surface WO_x sites and the absence of a NiWO­₄ compound. The catalytic activity of each catalyst was tested in a fixed-bed reactor and the products were analyzed by online gas chromatography (GC) with a flame ionization detector (FID). The supported tungsten oxide catalysts were found to exhibit low activity for ethylene dimerization. The limited conversion was related to coking of the catalyst surface and the amount of coking closely correlated with increasing nickel loading.