Heterogeneous oligomerization of ethylene over highly active and stable Ni-AlSBA-15 mesoporous catalysts

Abstract

Ni-AlSBA-15 oligomerization catalysts (2.6 wt% Ni, Si/Al = 7) were prepared by post-synthesis alumination of SBA-15 silica with sodium aluminate, followed by ion exchange with nickel. Characterization techniques, including powder X-ray diffraction, N 2 sorption, TEM, 27 Al, and 29 Si MAS NMR proved the perfect pore system of the SBA-15 materials, with aluminum tetrahedrally mainly coordinated in the silica framework. Ni-AlSBA-15 exhibited outstanding catalytic behavior in the oligomerization reaction of ethylene. At 150 °C and 3.5 MPa, in both batch and flow mode, the catalyst was highly active (up to 175 g of oligomers per gram of catalyst per hour), selective (C4, C6, C8, and C10 olefins, no cracking products), and stable (high conversion during 80 h on stream). These performances were superior than those exhibited by other Ni-based heterogeneous catalysts, without using alkylaluminum cocatalysts. A mechanistic pathway involving metallacyclic intermediates is supported by the experimental results.