Preparation And Characterization Of Ni/SiO₂@TiO₂ Core-Shell Catalyst For One-Step Synthesis Of 2-Propylheptanol From N-Valeraldehyde

2-Propylheptanol is an important plasticizer alcohol.The self-condensation of n-valeraldehyde and hydrogenation of 2-propyl-2-heptenal are the two important steps for the industrial production of 2-propylheptanol.A reaction integration of these two steps can simplify process flow,decrease energy consumption and improve process economy.To improve the competitiveness of n-valeraldehyde self-condensation,a core-shell multifunctional catalyst Ni/SiO₂@TiO₂ was designed and prepared for this reaction integration and thus one-step synthesis of 2-propylheptanol with high selectivity from n-valeraldehyde was achieved in this thesis.Firstly,SiO₂@TiO₂ samples were prepared using sol-gel technique.The effects of ammonia amount,TBOT amount and reaction time on their structures were investigated.Based on SEM,TEM and XRD analyses,the suitable conditions for preparation of SiO₂@TiO₂ samples were obtained as follows:a mass ratio of SiO₂:ammonia:TBOT=0.3:0.9:2,and a reaction time=3 h.The activity evaluation results show that anatase SiO₂@TiO₂ has a better catalytic performance for n-valeraldehyde self-condensation:a2-propyl-2-heptenal selectivity of 96.0%was achieved at a n-valeraldehyde conversion of 94.5%.Secondly,a core-shell structured multifunctional catalyst Ni/SiO₂@TiO₂ was prepared by impregnation and subsequent sol-gel process.The structure of Ni/SiO₂@TiO₂ was confirmed with the help of SEM,TEM,TEM-EDS and ICP-OES analyses.The influences of metal loading,TBOT amount and structure-directing agents on Ni/SiO₂@TiO₂ structure and catalytic performance were investigated.The suitable Ni loading was 2.5 wt.%,and the suitable mass ratio of Ni/SiO₂:ammonia:TBOT=0.3:0.9:2.Increasing the thickness of TiO₂ shell could inhibit the direct hydrogenation of n-valeraldehyde and promote its self-condensation reaction but simultaneously disfavour the hydrogenation of 2-propyl-2-heptenal to 2-propylheptanol.The activity evaluation results showed that Ni/SiO₂@TiO₂ exhibited an excellent catalytic performance for one-step synthesis of 2-propylheptanol from n-valeraldehyde.The suitable reaction conditions for one-step synthesis of 2-propylheptanol were determined as follows:a weight percentage of Ni/SiO₂@TiO₂=15 wt.%,a reaction temperature=190℃,a reaction pressure=3 MPa and a reaction time=10 h.Under the above reaction conditions,the conversion of n-valeraldehyde was 100%,the yield of 2-propylheptanol was 77.9%,and the sum of C₁₀+C₅ selectivity reached 98.2%.Finally,the reaction kinetics of one-step synthesis of 2-propylheptanol from n-valeraldehyde catalyzed by Ni/SiO₂@TiO₂was studied and a kinetic model was established.The kinetic model testing results indicate that the values predicted by the kinetic model agree well with the experimentally measured data.