金属氧化物复合催化剂的制备及其催化性能研究

发布时间：2018-06-03 01:12

本文选题：金属氧化物 + 复合催化剂　；参考：《沈阳工业大学》2017年硕士论文

【摘要】：本文针对金属氧化物催化剂的传统制备工艺繁琐,反应条件苛刻,产率低,不适合工业化生产等特点进行了改进,并利用贵金属掺杂及多种半导体金属氧化物的复合等方法提高其催化性能。采用醋酸锌、硝酸银及硝酸铋作原料,柠檬酸作络合剂,通过化学沉淀法制得前驱体,经高温煅烧制备了Ag/ZnO-Bi_2O_3,Ag/ZnO,Ag/Bi_2O_3,Bi_2O_3/ZnO四种金属氧化物复合催化剂,通过X射线衍射(XRD),扫描电镜(SEM),透射电镜(TEM),BET比表面积仪和紫外-可见漫反射吸收光谱(UV-Vis)等分析方法对产物结构、形貌,比表面积,光学性质等进行了表征,并对该催化剂光催化降解模拟有机染料废水和催化羟醛缩合反应进行了研究。本文制得不同原料配比的Ag/ZnO-Bi_2O_3复合催化剂,形貌分析表明复合催化剂由单质银晶粒、氧化锌块状晶体,氧化铋晶片结构组成,其中ZnO形貌为较大块状晶体,而Ag晶粒和Bi_2O_3晶片比较均匀分散在ZnO晶体表面,复合良好。利用Ag和Bi_2O_3对ZnO进行改性,有效地降低了ZnO的禁带宽度,使其光谱响应范围扩展到423 nm处,所制得Ag/ZnO-Bi_2O_3复合催化剂在230-400 nm紫外光区的吸收明显加强。光催化实验结果表明,紫外光照条件下,当原料摩尔比为醋酸锌:硝酸铋:硝酸银=1:0.1:0.25时Ag/ZnO-Bi_2O_3复合催化剂的催化活性最高,对20mg/L的甲基橙溶液降解率可达95%以上,降解时间为2.5 h;加入体积浓度为0.091的过氧化氢溶液作为光生电子捕获剂,可以和Ag/ZnO-Bi_2O_3复合催化剂产生协同作用,2h可充分降解。该复合催化剂在可见光照射1.5h时,对浓度为20mg/L罗丹明B溶液降解率达97.6%;光照2.5h,罗丹明B降解率达99.8%,效果显著,说明改性后的复合催化剂在可见光区域也具有较高的催化效率。Ag/ZnO催化降解罗丹明B溶液1.5h,降解率为99.9%;Ag/Bi_2O_3催化降解4h降解率达98.7%,继续延长降解时间,降解率变化不明显;Bi_2O_3/Zn O催化降解速率较快,时间30min降解率已达97.99%,综上所述,采用Ag和Bi_2O_3对ZnO进行改性,可有效的增强ZnO的光谱响应强度,提高其光催化效率。采用金属氧化物催化剂进行催化合成查尔酮实验,结果表明Bi_2O_3/ZnO复合催化剂可以有效的减少反应副产物,提高查尔酮的产率,催化剂用量8.8%,反应2h,查尔酮产率达92.5%,催化剂具有良好的稳定性,可以重复使用3次以上。
[Abstract]:In this paper, the traditional preparation process of metal oxide catalyst is complicated, the reaction conditions are harsh, the yield is low, and it is not suitable for industrial production. The catalytic performance was improved by the methods of noble metal doping and the recombination of various semiconductor metal oxides. Using zinc acetate, silver nitrate and bismuth nitrate as raw materials and citric acid as complexing agent, the precursor was prepared by chemical precipitation method. Four kinds of metal oxide composite catalysts, Ag/ ZnO-Bi2O3Ag- / ZnO2O3Ag-P / ZnO2O3 / Bi2O3 / Bi2O3 / ZnO, were prepared by calcining the precursor at high temperature. The structure, morphology, specific surface area and optical properties of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) Tem BET surface area analysis and UV-Vis-UV diffuse reflectance spectroscopy (UV-Vis). The photocatalytic degradation of simulated organic dyestuff wastewater and the catalytic condensation of hydroxyaldehydes over the catalyst were studied. In this paper, Ag/ZnO-Bi_2O_3 composite catalysts with different ratios of raw materials were prepared. The morphology analysis showed that the composite catalysts were composed of single silver grain, zinc oxide bulk crystal and bismuth oxide wafer structure. Among them, the morphology of ZnO was large bulk crystal. On the other hand, Ag crystal and Bi_2O_3 wafer are uniformly dispersed on the surface of ZnO crystal, and the composite is good. By modifying ZnO with Ag and Bi_2O_3, the band gap of ZnO was effectively reduced, and the spectral response range of ZnO was extended to 423 nm. The absorption of Ag/ZnO-Bi_2O_3 composite catalyst in the UV region of 230-400 nm was obviously enhanced. The results of photocatalytic experiments show that the catalytic activity of Ag/ZnO-Bi_2O_3 composite catalyst is the highest when the molar ratio of raw material is zinc acetate: bismuth nitrate: silver nitrate 1: 0.1: 0.25, and the degradation rate of methyl orange solution of 20mg/L can reach more than 95%. The degradation time was 2.5 h and the photoelectron trapping agent was added with hydrogen peroxide solution of 0.091 volume concentration. The photoelectron trapping agent could produce synergistic effect with Ag/ZnO-Bi_2O_3 complex catalyst and could be fully degraded for 2 hours. When exposed to visible light for 1.5h, the degradation rate of 20mg/L Rhodamine B solution reached 97.6k, and the degradation rate of Rhodamine B reached 99.8cm after 2.5 h irradiation. The results show that the modified composite catalyst also has higher catalytic efficiency in visible light region. Ag- / ZnO catalytic degradation of Rhodamine B solution is 1.5h, and the degradation rate is 99.9Ag- / Bi2O-3 for 4 h, and the degradation rate reaches 98.7g / h, and the degradation time continues to be prolonged. The degradation rate of Bi2O3 / Zn-O was not obvious, and the degradation rate of 30min reached 97.999.In conclusion, the modification of ZnO by Ag and Bi_2O_3 can effectively enhance the spectral response strength of ZnO and improve its photocatalytic efficiency. Metal oxide catalyst was used to catalyze the synthesis of chalcone. The results showed that Bi_2O_3/ZnO composite catalyst could effectively reduce the by-products of the reaction and increase the yield of chalcone. The amount of catalyst was 8.8 and the reaction time was 2 hours. The yield of chalcone reached 92.5%. The catalyst had good stability and could be reused for more than three times.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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