【作者】 张伟；

【导师】 刘葵；

【作者基本信息】 广西师范大学 ， 化学工程与技术， 2017， 硕士

【摘要】 镧镍复合氧化物是应用广泛的催化剂材料,将其用于过氧化氢分解反应的催化剂的研究较少见报道。本文以氯化镧和氯化镍为原料,以草酸和碳酸钠为沉淀剂,采用沉淀法制备了氧化镧和镧镍复合氧化物LaNiO3与La2NiO4,研究了氧化镧和镧镍复合氧化物对过氧化氢分解反应的催化性能及催化反应动力学,并对镧镍复合氧化物催化反应前后的结构进行了分析。全文的主要研究内容和结果如下:1.采用沉淀法制备了氧化镧、镧镍复合氧化物LaNiO3与La2NiO4。以氯化镧为原料,采用草酸作为沉淀剂,在40℃反应1h,所得沉淀产物在700℃煅烧2h,可制备得到氧化镧。沉淀反应温度、溶液的pH和加料方式都影响氧化镧的粒径分布。随沉淀反应温度的增加、溶液pH的降低,氧化镧的粒度逐渐增大。沉淀反应温度为40℃所制备的氧化镧呈柱状结构,升高反应温度,氧化镧由呈柱状结构向片状结构转变。以氯化镧与氯化镍为原料,控制nLa与nNi的比例为1:1,以碳酸钠为沉淀剂,在30℃沉淀反应1h,所得碳酸钠沉淀前驱体于700℃煅烧2h即可制备LaNi03;当nLa与nNi的比例调整至2:1时,以草酸作为沉淀剂,在80℃下搅拌反应1h,所得草酸沉淀前驱体于1000℃煅烧2h,或碳酸钠作为沉淀剂,在30℃下搅拌反应1h,所得碳酸钠沉淀前驱体于800℃煅烧2h,可制备La2NiO4。以草酸作沉淀剂所制备的La2Ni04呈不规则棒状结构,而用碳酸钠作沉淀剂制备的La2NiO4呈不规则的块状结构,用碳酸钠作沉淀剂制备的LaNi03呈现不规则球形颗粒状结构。LaNiO3、La2NiO4样品表面有La3+与Ni2+离子,同时可能会有Ni3+离子共存。氧化镧制备过程的前驱体产物为La2(C2O4)3·10H2O,在受热分解的过程逐渐失去结晶水、生成中间产物La202CO3,最后分解生成目标产物La2O3。使用草酸和碳酸钠作沉淀剂制得的镧镍复合氧化物前驱体分别是含有结晶水的镧镍草酸盐和镧镍碳酸盐混合物,在煅烧过程中有La2O2CO3、La2O3与NiO这些中间相生成,最后生成LaNiO3或La2NiO4。LaNi03的热稳定性比La2NiO4差,当温度高于1000℃,LaNiO3会分解为La2NiO4与NiO的混合物。2.研究了氧化镧、镧镍复合氧化物LaNiO3和La2NiO4对过氧化氢分解反应的催化性能。LaNiO3和La2NiO4对过氧化氢的分解反应有明显的催化作用,LaNiO3的催化性能最高高于La2NiO4的催化性能。La2O3,NiO,Ni2O3对过氧化氢的分解反应基本无催化效果。温度和反应时间是影响LaNiO3和La2NiO4催化过氧化氢分解反应的重要因素,升高温度和延长反应时间都能提高过氧化氢的分解率。在反应温度为35℃,反应时间为40min时,LaNiO3催化过氧化氢分解反应的分解可接近100%。沉淀反应时间,沉淀反应温度,沉淀产物煅烧温度等都会影响所制备的LaNiO3的表面形貌,从而影响LaNiO3的催化性能。LaNiO3的比表面积越大,其催化性能越好。以碳酸钠为沉淀剂,在30℃沉淀反应1h,并于700℃煅烧2h所制备的LaNiO3催化性能较好。过氧化氢分解反应过程中LaNiO3、La2NiO4未发生化学反应,其物相和组成没有改变,但LaNiO3、La2NiO4的形貌发生一定程度的改变,有细小颗粒增多的现象。3.研究了 LaNiO3和La2NiO4催化过氧化氢分解反应的动力学借助MATLAB软件,拟合了LaNiO3和La2NiO4催化过氧化氢分解反应的反应级数,结果表明,镧镍复合氧化物LaNiO3和La2NiO4催化过氧化氢分解反应的反应级数相接近,约为0.54。LaNiO3和La2NiO4对过氧化氢的分解反应具有类似的催化作用,催化反应动力学方程可用r=kCH2O20.54表示。LaNiO3催化过氧化氢分解反应的活化能为31.96kJ/mol,La2NiO4催化过氧化氢分解反应的活化能能为48.54kJ/mol,La2NiO4与LaNiO3均能降低H2O2分解反应的活化能。LaNiO3对H2O2分解反应的催化能力比La2NiO4对H2O2分解反应的催化能力更强。因此,LaNiO3是过氧化氢分解反应的理想催化剂。更多还原

【Abstract】 Lanthanum-nickel composite oxides are widely used as catalysts.It is rarely reported that lanthanum-nickel composite oxides are used as the catalysts for the decomposition reaction of hydrogen peroxide.In this paper,lanthanum oxide and lanthanum-nickel composite oxides LaNiO3 and La2NiO4 were prepared by precipitation method,using lanthanum chloride and/or nickel chloride as raw materials,and oxalic acid and/or sodium carbonate as precipitants.The catalytic performance,catalytic reaction kinetics and catalyst structure before and after the decomposition reaction of hydrogen peroxide were studied.The main contents and results are as follows:1.Lanthanum oxide and lanthanum-nickel complex oxides LaNiO3 and La2NiO4 were prepared by precipitation method.Lanthanum oxide was prepared using lanthanum chloride as the raw material and oxalic acid as the precipitant,under the precipitation conditions of 40℃ and 1h,and the calcination conditions of 700℃ and 2h.The particle size distribution of lanthanum oxide was affected by the precipitation temperature,the pH of the solution and the adding method of the feed solutions.With the increase of precipitation temperature,decrease of pH of solution,the particle size of lanthanum oxide increased gradually.The lanthanum oxide prepared at the precipitation reaction temperature of 40℃ was columnar,and changed from columnar to lamellar as the reaction temperature increased.LaNiO3 was prepared using lanthanum chloride and nickel chloride as raw materials with the ratio of nLa to nNi of 1:1,and sodium carbonate as the precipitant,after reacted at 30℃ for 1h and calcined at 700℃ for 2h.When adjusting the ratio of nLa:nNi to 2:1,La2NiO4 was prepared using oxalic acid as the precipitant after the raw materials and the precipitant were stirred at 80℃ for 1h and the precipitation precursor was calcined at 1000℃ for 2h,or using sodium carbonate as the precipitant after the raw materials and the precipitant were stirred at 30℃ for 1h and precipitation precursor was calcined at 800℃ for 2h.La2NiO4 with the irregular rod structure was obtained by using oxalic acid as the precipitant,while La2NiO4 with the irregular block structure and LaNiO3 with the irregular spherical granular structure were obtained by using sodium carbonate as the precipitant.There were La3+and Ni2+ions at the surface of LaNiO3 and La2NiO4.Ni3+ion might coexist at the surface of LaNiO3 and La2NiO4.The precursor during preparation of lanthanum oxide was La2(C2O4)3·10H2O,which gradually lost its crystal water and formed the intermediate product La2O2CO3 and decomposed finally to La2O3.The precursors of lanthanum-nickel complex oxide were lanthanum-nickel oxalates and lanthanum-nickel carbonates containing crystalline water when using oxalic acid and sodium carbonate as precipitants,respectively.La2O2CO3,La2O3 and NiO were generated,and finally LaNiO3 or La2NiO4 was generated during the calcination.The thermal stability of LaNiO3 was weaker compared to La2NiO4.LaNiO3 was decomposed into a mixture of La2NiO4 and NiO when calcined at the temperature higher than 1000 0C.2.The catalytic performance of lanthanum oxide and lanthanum-nickel complex oxides LaNiO3 and La2NiO4 to the decomposition of hydrogen peroxide was studied.LaNiO3 and La2NiO4 had obvious catalytic effects on the decomposition of hydrogen peroxide.The catalytic performance of LaNiO3 was higher than that of La2NiO4.La2O3,NiO and Ni2O3 had no catalytic effect on the decomposition of hydrogen peroxide.Temperature and reaction time are important factors affecting the catalytic decomposition of hydrogen peroxide.Higher temperature and longer reaction time can improve the catalytic decomposition rate of hydrogen peroxide.The decomposition percentage of hydrogen peroxide was close to 100%at 35 0C and the reaction time of 40min when using LaNiO3 as the catalyst.The precipitation time,the precipitation temperature and the calcination temperature during preparation of LaNiO3 had a great influence on the surface morphology of LaNiO3,which influenced the catalytic performance of LaNiO3.The larger the specific surface area of LaNiO3,the better its catalytic performance.The catalytic performance of LaNiO3 was better,which was prepared at the precipitation temperature of 30℃ for 1h and calcination temperature of 700℃ for 2 h,using sodium carbonate as the precipitant.During the decomposition of hydrogen peroxide,LaNiO3 and La2NiO4 did not change to other substances.However,the tiny particles of LaNiO3 and La2NiO4 increased after the decomposition of hydrogen peroxide.3.The kinetics of decomposition of hydrogen peroxide catalyzed by LaNiO3 and La2NiO4 was studied.The reaction order of LaNiO3 and La2NiO4 catalytic decomposition of hydrogen peroxide was fitted,using MATLAB software.The results show that the reaction order of LaNiO3 and La2NiO4 catalytic decomposition of hydrogen peroxide is close to 0.54.LaNiO3 and La2NiO4 had similar catalytic effects on the decomposition reaction of hydrogen peroxide,and the catalytic reaction kinetic equation was r=kC0.54H2O2.The activation energy of LaNiO3 and La2NiO4 for the decomposition of hydrogen peroxide was 31.96kJ/mol and 48.54kJ/mol,respectively.Both La2NiO4 and LaNiO3 could reduce the activation energy of decomposition reaction of hydrogen peroxide.The catalytic ability of LaNiO3 for the decomposition reaction of hydrogen peroxide is stronger than that of La2NiO4.Therefore,LaNiO3 is an ideal catalyst for the decomposition of hydrogen peroxide.更多还原