One-step non-hydrolytic sol-gel synthesis of mesoporous SiO2-Al2O3-NiO catalysts for ethylene oligomerization

Mesoporous SiO2-Al2O3-NiO mixed oxide catalysts with different Si/Al ratio and a Ni content of ≈5.5 wt% have been prepared by a simple, one-step non-hydrolytic sol-gel route and evaluated in the oligomerization of ethylene. The catalysts were characterized by TEM-EDX, N2-physisorption, NH3-TPD, powder XRD, 29Si and 27Al MAS-NMR, XPS, and H2-TPR. The Si/Al ratio was found to influence both the texture and the acidity of the materials. According to XRD, part of the Ni formed NiO crystallites, but according to XPS, no bulky NiO was detected at the surface of the catalysts. XPS spectra and TPR experiments are consistent with the formation of dispersed Ni2+ species strongly interacting with the surface. The samples with high Al content displayed excellent performances with very high specific activity up to 270 mmol ethylene converted per g of catalyst per hour at 150 °C, and a percentage of butenes in the products of ≈70%. These catalysts compare well with model catalysts prepared by time-consuming multistep procedures from expensive ordered mesoporous silica supports.