Zn/Co-HMS催化氧化异戊醇生成异戊酸

Isoamyl alcohol to Isovaleric acid under Catalytic Oxidation of Zn/Co-HMS

以正硅酸四乙酯为硅源,十二胺为模板剂,通过溶胶凝胶法制备了HMS,Co掺杂的六方介孔硅分子筛(Co-HMS(100));以Co-HMS(100)为载体,硝酸锌、乙酸锌、硫酸锌、氯化锌为Zn源,通过浸渍法制备了负载型催化剂Zn/Co-HMS(100)-N,Zn/Co-HMS(100)-Ac,Zn/Co-HMS(100)-S和Zn/Co-HMS(100)-Cl。通过XRD,FT-IR,TG,NH3-TPD,SEM和N2吸附脱附对不同催化剂进行了表征,并研究了不同催化剂对异戊醇催化氧化生成异戊酸的影响。结果表明:掺杂Co与负载Zn未改变HMS分子筛的六方介孔结构;在550℃焙烧温度下只有硝酸锌和乙酸锌以Zn O的形式存在于载体中;Zn O有助于降低催化剂弱酸含量,有利于反应进行;掺杂Co可以增加催化剂的孔径,有利于反应物与产物扩散。此外,以硝酸锌为Zn源的催化剂Zn/Co-HMS(100)-N较其他3种Zn源催化剂表现出更好的催化效果。在Zn/Co-HMS(100)-N用量为0.5g、反应温度为120℃、反应时间为8h条件下,异戊醇的转化率、异戊酸的收率与选择性分别达到52.2%,26.9%和51.5%;而催化剂Zn/Co-HMS(100)-S和Zn/Co-HMS(100)-Cl几乎没有催化效果。最后,对该催化反应机理进行了初步探讨,发现该反应符合自由基反应过程。

Abstract： Zn/Co-HMS （100） was prepared via wetness impregnation with Co-doped hexagonal mesoporous silica zeolite （HMS） as the support, which was synthesized by sol-gel method and [ Zn（NO3）2· 6H2O], [Zn （CH3 COO）2 · 2H20], [ZnSO4 · 7H2O] , ZnCl2 as Zn precursor. The prepared catalysts were character- ized by XRD, FT-IR, TG, NH3-TPD, SEM and N2 adsolption-desorption technique, and their perforlances of catalyzing isoamyl alcohol to isovaleric acid were also investigated. The results suggested that doping and loading did not alter the hexagonal mesopore structure of HMS; only [ Zn （NO3）2 · 6H2O] and [ Zn （CH3COO）2 · 2H2O] can exist in catalysts as ZnO form under 550℃, which can decrease the amount of weak acids. Besides, doping Co can increase the diameter of catalysts, facilitating the transit of the substrates and outputs. Using [ Zn（NOB） 2 · 6H2O] as the precursor to prepare Zn/Co-HMS （100） -N can reduce the particle diameter of the catalyst and thus increase its unifoml distribution. Furthemlore, Zn/Co-HMS （100）- N exhibited the highest catalytic peffomlance than the other catalysts. Under the condition of 0.5 g of Zn/Co- HMS （100）-N added, reaction temperature 120℃ , reaction time 8h, the conversion rate of isoamyl alcohol and the yield and selectivity of isovaleric acid were 52.2% , 26.9% and 51.5% , respectively. Finally, the catalytic mechanism of Zn/Co-HMS （100）-N was discussed and the reaction mechanism of the catalyst was found to fit free radical reaction.