Buserite型氧化锰催化叔丁基过氧化氢歧化分解反应动力学

Chemical Kinetics of Disproportionation Decomposition of tert-Butyl Hydroperoxide Catalyzed by Buserite-type Manganese Oxides

以MnSO_4·H_2O为锰源,K_2S_2O_8为氧化剂,制备了4种含有不同层间阳离子(Me,Me=Mg^(2+)、Co^(2+)、Ni^(2+)、Cu^(2+))的buserite型氧化锰(Me-buserites)。采用X射线衍射(XRD)、电感耦合等离子体原子发射(ICP-AES)和N2吸附–脱附(BET)对制成Me-buserites的晶相结构、元素组成和比表面积进行了表征。采用25 m L间歇式玻璃反应器,考察了Me-buserites催化叔丁基过氧化氢歧化分解反应动力学。反应动力学分析表明:反应底物叔丁基过氧化氢浓度项反应级数为2,Me-buserites形式浓度项反应级数为1,总反应级数为3;表观活化能为56~125 k J/mol。与动力学拟合结果相一致的反应机理是由前置平衡和速控两个反应步骤组成。基于338 K反应温度准二级速率常数和0.5 h反应时间累积O_2体积决定的活性顺序为Cu-buserite>Mg-buserite>Ni-buserite>Co-buserite;在选定反应条件下,所有Mebuserites的叔丁醇选择性均为100%。

The series of four buserite-type layered manganese oxides （Me-buserites） with different interlayer cations （Me, Me = Mg2＋, Co2＋, Ni2＋, Cu2＋） were synthesized by using both MnSO4＋H20 as Mn source and K2S208 as oxidant. The as-synthesized Me-buserites were characterized by X-ray diffraction （XRD）, inductively coupled plasma-atomic emission spectrometry （ICP-AES） and N2 adsorption-desorption （BET）, in order to determine their crystal phases, elemental compositions and specific surface areas, respectively. In a 25 mL batch glass reactor, the disproportionation decomposition of tert-butyi hydroperoxide was kinetically investigated with the above Me-buserites as catalysts. The kinetic analyses show that the rate law established herein is second order in tert-butyl hydroperoxide, first order in Me-buserites and then third order overall, and that the apparent activation energy ranges from 56 kJ/mol to 125 kJ/mol. In accordance with the kinetic fittings, the proposed mechanism comprises two elementary reaction steps： pre-equilibrium step and rate-determining step. In terms of the pseudo-second-order rate constant and the half an hour-accumulated 02 volume （both obtained at 338 K）, the activity follows the order of Cu-buserite 〉 Mg-buserite 〉 Ni-buserite 〉 Co-buserite. And a 100% selectivity towards tert-butyl alcohol is achieved over all the Me-buserites un-der selected reaction conditions.