Ethylene trimerization using half-sandwich titanium-based catalysts supported on mesoporous silica modified with ionic liquids

Linear alpha olefins (LAOs) are produced industrially via ethylene oligomerization using catalytic methods. The cost-effective separation process has sparked significant interest in the selective oligomerization of ethylene to produce alpha-olefins, including 1-hexene (1-C6), in multi-product commercial processes. In addition, the utilization of immobilized catalysts is crucial because of their reduced environmental impact, ease of catalyst separation, recyclability, and transportability. Furthermore, the use of immobilized catalysts simplifies the purification process, making it easier to isolate pure products. In the present study, mesoporous silica (MS) was first modified with ionic liquids (ILs) consisting BF4- and Br- counter-anions to prepare IL-BF4@MS and IL-Br@MS, respectively. Then 12 catalysts were synthesized through immobilization of the half-sandwich catalysts with different bridges on the surface of MS, IL-Br@MS, and IL-BF4@MS and characterized by BET, TGA, and SEM-EDX-Mapping analyses. UV-Visible spectroscopy showed a tetrahedral structure for the synthesized complexes. The activity and selectivity of the catalysts for the production of 1-hexene were studied under specific conditions, including an ethylene pressure of 8 bar, a temperature of 40 degrees C, and an Al/Ti ratio of 1:2000. The C1-IL-BF4@MS immobilized catalyst with cyclohexane middle bridge immobilized on MS modified with IL-BF4 revealed the highest activity (1199 kg 1-C6 molTi-1 center dot h-1) at a catalyst concentration of 1.5 mu mol. The lowest activity (138 kg 1-C molTi-1 center dot h-1) was obtained for both C3@MS and C4@MS catalysts. The surface of mesoporous silica (MS) was modified with imidazolium-based ionic liquids (ILs). Half-sandwich titanium-based catalysts were immobilized on the surface of IL-modified MS. Catalysts immobilized on IL-modified MS showed higher 1-hexene selectivity and activity compared with the unmodified MS. C1-IL-BF4@MS catalyst showed the highest activity of 1,199 kg 1-C6 molTi-1 center dot h-1. image