Synthesis Of Transition Metal Composite Oxides And Their Catalytic Performance

Transition metal composite oxide is an important kind of inorganic functional materials. Because of its special structure, it has been considered to have potential applications in electrode materials, catalysis materials, magnetic materials and gas-sensing materials. This paper focuses on the synthesis of transition metal composite oxides and their applications in esterification and waste water treatment. The main contents are as follows:ZnMn₂O₄ nano-catalyst has been synthesized by a co-precipitation method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicate that the sample can be indexed to tetragonal ZnMn₂O₄ and the particle size ranges from 20 to 50 nm. The obtained ZnMn₂O₄ nano-particles have been used as the catalyst for the synthesis of n-butyl acetate. Experimental results show that the sample calcined at 300℃has the highest catalytic activity. The influential factors including catalyst calcination temperature, acid-to-alcohol molar ratio, dosage of catalyst and reaction time on the yield of n-butyl acetate have also been investigated respectively and maximal esterification ratio up to 92.53% has been achieved under the following conditions: catalyst calcination temperature = 300℃, n(acid):n(alcohol) = 1.8:1, the dosage of the ZnMn₂O₄ catalyst = 0.3% (in total mass of reactants) , reaction time = 240 min and esterification reaction temperature = 120℃. The kinetics of the reaction was found to be: -dC_A/dt=9. 87×10^-4C_AC_B. The mechanism of the catalytic process is also discussed.The ZnMn₂O₄ was also used as the catalyst for the synthesis of cyclohexyl acetate. The esterification ratio reaches 89.34% under the optimum conditions: n(acid):n(cyclohexanol) = 1.9:1, the dosage of the ZnMn₂O₄ catalyst = 0.25% (in total mass of reactants), reaction time = 210 min and esterification reaction temperature = 135℃. The kinetic equation is -dC_A/dt=1. 81×10^-3C_AC_B.Zn-Mn-Al hydrotalcites precursors were prepared by co-precipitation method. Then Al-doped ZnMnO₃ composite oxides with average particle size of 50 nm were prepared after calcination of the precursors. With the as-prepared composite oxides as catalyst and H₂O₂ as oxidant, the decoloration of methylene blue was studied. The experimental results show that the sample calcined at 500℃has the highest catalytic efficiency, and the decoloration rate of methylene blue reaches 92.59% within 240 minutes. The influential factors including initial concentration of methylene blue, initial concentration of H₂O₂ and the catalyst dosage were also studied respectively. Kinetic study of the catalytic reaction shows that the reaction kinetics order is 2.27 and the reaction rate constant is 0.018 (mol·L^-1)^-1.27·min^-1.