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Hydrolytic vs. nonhydrolytic sol-gel routes to prepare mixed oxide catalysts for ethylene oligomerization

Abstract : The sol-gel route (SG) offered an interesting way for the preparation of mixed oxides. Two different approaches were explored in this work, first one we showed that SixAly catalysts can be successfully prepared by HSG route and show their activity for esterification. Two parameters of the preparation were screened: the Al2O3 (or Si/Al ratio) and pH value. NHSG (alcohol route) were successfully used also to prepare (Six-Aly) mixed oxides from non-expensive precursors. Two types of alcohol, ethanol and tBuOH were used as a solvent and oxygen donor in the same time. The SixAly mixed oxides were also prepared by NHSG (ether route) and compared with the same composition samples prepared by alcohol route The Si/Al ratio can be easily controlled, knowing that it plays an important role in the structure, texture, acidity of the samples. The composition of all samples prepared by both alcohol and ether routes show good control on composition. The texture is strongly depend on the Si/Al and on type of solvent, the N2-adsorption desorption presented that samples prepared with EtOH and ether show high specific surface area and it decrease with Si% decrease in the samples. The structure of all samples were studied by XRD and NMR , the results obtained showed that all the mixed oxides are amorphous. Second part we showed that SixAlyNiz catalysts can be successfully prepared by a one-step NHSG route for ethylene oligomerization. Two parameters of the preparation were screened: the Al2O3 (or Si/Al ratio) and the NiO contents. The NHSG synthesis used in this part is based on the one pot reaction of commercially available reagents (SiCl4, AlCi3,Ni(acac)2 ) with diisopropylether (iPr2O) at 110 °C in dichloromethane. The physico-chemical properties of the solids produced were studied and correlated with the catalytic performance. NHSG provides a simple one-step route to mesoporous materials with a good control of the composition and relatively high surface areas and pore vo lumes. All silica-alumina and alumina supported catalysts were significantly active in ethylene oligomerization while the activity of the silica-based catalyst was very low. The catalysts with the higher Al2O3 contents Si0Al90Ni10 and Si10Al80Ni10 exhibit the highest catalytic activity for NiO loadings equal to 10 wt.%. The nature of the support strongly determines the acidic properties of the catalyst. Furthermore, we showed that the specific activity in oligomerisation reaction decreases when the NiO loading increases.
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Submitted on : Wednesday, June 29, 2022 - 6:02:42 AM
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Atheer Hasan Yas Al Khudhair. Hydrolytic vs. nonhydrolytic sol-gel routes to prepare mixed oxide catalysts for ethylene oligomerization. Material chemistry. Université Montpellier, 2021. English. ⟨NNT : 2021MONTS103⟩. ⟨tel-03708150⟩

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