不同形貌纳米CuM₂O₄（M=Co,Cr）制备及其对AP热分解催化性能研究

【作者】 张宇；

【导师】 张国防；

【作者基本信息】 陕西师范大学 ， 工程硕士（专业学位）， 2020， 硕士

【摘要】 纳米燃速催化剂是一类能够有效催化高氯酸铵（AP）热分解的纳米材料,影响纳米燃速催化剂催化性能的主要因素是其形貌和比表面积。本文通过微波法和静态回流法制备了不同形貌的CuCr₂O_4,通过水热法制备了不同形貌的CuCo₂O_4,采用XRD,SEM,TEM,BET,XPS等手段表征了它们的形貌和结构,采用DSC和TG技术研究了不同形貌的CuCr₂O_4和CuCo₂O_4对于AP热分解的催化活性,研究内容如下:（1）以氟化铵（NH4F）为形貌调节剂,六亚甲基四胺（HMT）为沉淀剂,通过微波法制备了CuCr₂O_4,研究发现反应时间,NH4F加入量和最终煅烧温度对于CuCr₂O_4样品形貌和纯度有较大的影响,在经过一系列实验后发现,当原料的摩尔比为Cu²⁺:Cr³⁺:NH₄F:HMT=1:2:5:5,反应时间为40 min,煅烧温度为400℃时制备的样品形貌为15-40 nm厚的纳米片状立方相CuCr₂O_4样品M2,分散性好,比表面积大(95.41 m²·g^-1),对于AP热分解的催化效果最好,可以将AP热分解的高温分解温度从403.4℃降低至330.3℃,使AP的表观分解热从-746.53J.g^-1增加到-1237.06 J·g^-1。（2）以柠檬酸三钠（TSC）为形貌调节剂,HMT为沉淀剂,使用静态回流法制备了CuCr₂O_4。研究发现,煅烧温度对于样品形貌影响最大,煅烧温度在350℃时,样品R1形貌为5 nm厚的纳米片状CuCr₂O_4,样品无晶型;煅烧温度为380℃时,样品R2形貌为团聚的纳米片状CuCr₂O_4,纳米片的表面附着纳米粒子,有部分CuCrO4杂质,锻烧温度提高到400℃时,样品R3形貌为纳米粒子状立方相CuCr₂O_4,当温度升高到500℃时,样品R4形貌为纳米粒子状四方相CuCr₂O_4。经过BET测试发现随着煅烧温度升高,CuCr₂O_4的比表面积逐渐减小(从88.34m²·g^-1降低至13.37 m²·g^-1),经DSC和TG测试表明,样品R4比表面积最小但是催化效果最好,这是由于样品R1和R2含有部分的CuCrO4。（3）采用水热法制备了纳米CuCo₂O_4。以尿素作为沉淀剂,不加入形貌调节剂可制备出粒径为20-50 nm的纳米粒子状CuCo₂O_4;以尿素作为沉淀剂,NH4F为形貌调节剂制备出直径为50-120 nm,长度为100-800 nm的纳米棒状CuCo₂O_4;以HMT为沉淀剂,NH4F为形貌调节剂,制备出的CuCo₂O_4为厚度为20-40 nm纳米片状堆叠的三维结构;以HMT为沉淀剂,TSC为形貌调节剂,制备出的CuCo₂O_4为超薄纳米片状结构,纳米片厚度小于10 nm。经过BET,DSC和TG测试发现,超薄纳米片状结构的比表面积最大(100.22 m²·g^-1),对AP热分解的催化效果最好,其可以将AP热分解的高温分解温度从403.4℃降低至289.4℃。（4）通过DSC技术测试了微波法制备的纳米片状CuCr₂O_4样品M2和超薄纳米片状CuCo₂O_4样品A与AP以1:4比例混合时的热分解曲线。以Kissinger方程、Ozawa方程和积分法评价了样品A和M2催化AP热分解动力学过程,给出了相关热分解动力学参数及催化AP热分解过程的最可几机理函数。结果表明,加入样品A或M2后AP低温分解峰和高温分解峰合并为一个峰,可能是由于样品M2和样品A的加入改变了AP热分解的机理和历程,AP热分解过程由原来的两步反应变为了一步反应。通过计算发现向AP中添加样品M2和样品A均可以降低AP热分解的总活化能,说明两种样品对于AP的热分解都有良好的催化作用。更多还原

【Abstract】 Nano burning-rate catalysts（BRCs）are a type of nano materials those can effectively catalyze the thermal decomposition of ammonium perchlorate（AP）.The main factors affecting catalytic performance of nano BRCs are their morphologies and specific surface areas.In this thesis,nano CuCr₂O₄ was prepared by both microwave and reflow methods,and nano CuCo₂O₄ was prepared by hydrothermal method.Their morphologies and structures were characterized by XRD,SEM,TEM,BET,XPS.DSC and TG techniques were employed to study catalytic activity of CuCr₂O₄ and CuCo₂O₄ for thermal decomposition of AP.The main research contents are as follows:（1）Nano CuCr₂O₄ was prepared by microwave method with ammonium fluoride（NH4F）as morphology modifier and hexamethylenetetramine（HMT）as precipitant.It was found that reaction time,addition amount of NH4F and calcination temperature exhibit great influences on the morphology and purity of the nano CuCr₂O₄.After a series of experiment condition screening,it was found that when the molar ratio of the raw materials is Cu²⁺:Cr³⁺:NH₄F:HMT=1:2:5:5,reaction time is 40 min,and calcination temperature is 400℃,the morphology of the prepared CuCr₂O₄ sample is 15-40 nm thick nano-flaky cubic phase CuCr₂O₄（sample M2）,with good dispersion and large specific surface area(95.41 m²·g^-1).The sample M2 shows the most catalytic effect on AP thermal decomposition.The thermal decomposition temperature peak of AP shifted from 403.4℃ to 330.3℃,and the apparent decomposition heat of AP increased from-746.53 J·g^-1 to-1237.06 J·g^-1.（2）Nano CuCr₂O₄ was additionally prepared by static reflux method with trisodium citrate（TSC）as morphology regulator and HMT as precipitant.The studies found that calcination temperature has the greatest effect on the nano CuCr₂O₄ morphology.Ultra-thin CuCr₂O₄ sheet（sample R1）with ca.5 nm thickness was collected at 350℃;agglomerated nano-sheet CuCr₂O₄（sample R2）was collected at 380℃,its surface being doted by nano-particles,and the sample contains a small amount of CuCrO4;nano-particle cubic phase CuCr₂O₄（sample R3）was obtained at 400℃ and nano-particle tetragonal CuCr₂O₄（sample R4）was gathered at 500℃.The BET test results indicated that the specific surface area of CuCr₂O₄ decreases from 88.34 m²·g^-1 to 13.37 m²·g^-1 with the increase of the calcination temperature.DSC and TG tests showed that the specific surface area of sample R4 was the smallest,but the catalytic effect on the AP therma degradation was the best,due probably to CuCrO4 impurity particlesin both samples R1 and R2.（3）Nano CuCo₂O₄ was prepared by hydrothermal method.Nano-particle CuCo₂O₄ with particle size of 20-50 nm was prepared by using urea as precipitator without adding morphology regulator;nanorods CuCo₂O₄ with a diameter of 50-120 nm and a length of 100-800 nm was prepared by using urea as precipitant and NH4F as morphology regulator;taking HMT as precipitant and NH4F as morphology modifier,CuCo₂O₄ was prepared as 20-40 nm thick nano-sheets,which were stacked as three-dimensional structure.Using HMT as precipitant and TSC as morphology modifier,CuCo₂O₄ was prepared as ultrathin nanosheet,its thickness being less than 10 nm.The BET,DSC and TG tests results indicated that the specific surface area of the ultrathin nano-sheet CuCo₂O₄ was the largest(100.22m·g^-1),and it exhibited the best catalytic effect on the thermal decomposition of AP,the high-temperature decomposition peak of AP being advanced from 403.4℃ to 289.4℃.（4）The thermal decomposition kinetics of nano-sheets CuCr₂O₄（sample M2）and ultrathin nano-sheets CuCo₂O₄（sample A）mixed with AP in 1:4 ratio,respectively,were studied by DSC.The Kissinger equation,Ozawa equation and integral method were used to evaluate the kinetic process of catalytic thermal decomposition of AP with both samplesA and M2 as additives.The kinetic parameters of related thermal decomposition and the most feasible mechanism functions for catalytic thermal decomposition of AP were given.The results showed that the low temperature decomposition peak and high temperature decomposition peak of AP combined into one peak with addition of sample A or M2,which may be due to the addition of M2 and A changing the thermal decomposition mechanism and process of AP from the original two-step reaction to the one-step reaction.By calculation,it was found that the addition of M2 and A to AP can reduce the total activation energy of AP thermal decomposition,indicating that both samples have good catalytic effects on the thermal decomposition of AP.更多还原