文献类型：期刊文献

中文题名：金属有机框架衍生Co_(3)O_(4)在碳烟催化燃烧中应用

英文题名：Catalytic Combustion Performance of Co_(3)O_(4) Drived from Metal-Organic Framework

作者：石永凯[1];汪炜[1];刘雅洁[1];刘嘉俊[1];王丽[1];郭耘[1]

机构：[1]华东理工大学化学与分子工程学院,工业催化研究所,上海200237

年份：2021

卷号：45

期号：8

起止页码：952

中文期刊名：稀有金属

外文期刊名：Chinese Journal of Rare Metals

收录：CSTPCD;;EI(收录号：20213310790013);Scopus;北大核心:【北大核心2020】；CSCD:【CSCD2021_2022】；

基金：上海浦江计划项目(18PJD019)资助。

语种：中文

中文关键词：ZIF-67;Co3O4;规则形貌;碳烟燃烧

外文关键词：ZIF-67;Co3O4;regular morphology;soot combustion

摘要：以金属有机框架材料(ZIF-67)为前驱体,通过热解制备了具有规则形貌的四氧化三钴(Co_(3)O_(4))催化剂,并以紧密接触状态下的碳烟催化燃烧为模型,测试了催化剂制备条件,如结晶时间和热解温度对碳烟催化燃烧性能的影响。通过X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)和低温N2吸脱附实验发现400℃热解制备的Co_(3)O_(4)-400由细小纳米颗粒组成,呈现内部中空的规则多面体结构,有利于碳烟与催化剂接触;随着热解温度升高,催化剂的规则形貌被破坏,其中高温热解得到的Co_(3)O_(4)-700呈现大颗粒Co_(3)O_(4)杂乱排布。X射线光电子能谱(XPS)、氧气程序升温脱附(O_(2)-TPD)与碳烟程序升温还原(Soot-TPR)表明Co_(3)O_(4)-400表面具有较多的Co3+-O物种和氧空穴,加速了氧气的吸附与活化;而过高的热解温度导致催化剂表面Co3+-O、氧空穴含量以及活性氧物种活化速率降低。Co_(3)O_(4)-400具有较好的碳烟脱除性能,达到碳烟转化率50%所对应的温度(T50)为362℃,CO_(2)选择性为99.1%。
With the rapid development of automobile industry and sustained growing quantity of cars,nitrogen oxides(NOx)and soot particles from diesel engine exhaust are harmful to health and environment. Catalytic combustion is an efficient way to reduce soot particles emission. Cobalt trioxide(Co_(3)O_(4))has excellent catalytic oxidation performance and is suitable for various catalytic oxidation reactions. Metal organic frameworks have large specific surface area,controllable pore size and metal sites with unsaturated coordination,so it can be used as the template to prepare metal oxides. Therefore,cobalt trioxide(Co_(3)O_(4))with regular morphology prepared by pyrolyzing metal-organic framework(ZIF-67)from the precursors of 2-methylimidazole and Co(NO_(3))2·6 H_(2) O. Soot combustion in tight contact mode was taken as a model reaction to investigate the effect of preparation conditions,crystallization time and pyrolysis temperature on catalytic activity. The optimum pyrolyzing temperature was very important for preparing catalysts,for it not only guaranteed the decomposition of organic ligands but also avoided the particle sintering and agglomeration,and pore structure would collapse by high temperature. With the increase in pyrolyzing temperature,the activity of soot combustion decreased accordingly. The catalysts pyrolyzing at 400 ℃(Co_(3)O_(4)-400)reached 50% soot conversion at 362 ℃ with 99.1% CO_(2) selectivity,but when the pyrolyzing temperature increased to 700 ℃(Co_(3)O_(4)-700),the temperature for 50% conversion shifted 127 ℃ to higher temperature with the CO_(2) selectivity down to 92.9%. So the optimum preparation condition for Co_(3)O_(4) was set as the mole ratio of 2-methylimidazole to Co(NO_(3))2·6 H_(2)O at4,crystallization 24 h then pyrolyzing at 400 ℃. X-ray diffraction(XRD),transmission electron microscope(TEM),field emission scanning electron microscope(FESEM),N2 adsorption-desorption and Raman spectra were used to characterize the texture structure of Co_(3)O_(4). X-ray photoelectron spectroscopy(XPS)was used for chemical state. Oxygen temperature programmed desorption(O_(2)-TPD)and soot temperature programmed reduction(Soot-TPR)were used for the redox property of catalysts. The results showed that the pyrolysis temperature played a more important role than crystallization time on catalysts morphology,chemical state and redox property,which closely affected soot combustion activity. As characterized by XRD,FESEM and N2 adsorption-desorption experiments,Co_(3)O_(4) consisted of fine nanoparticles and arranged in regular polyhedral structure with internal hollow,which enhanced the contact between soot and catalyst. However,the regular morphology gradually destroyed by increasing pyrolysis temperature,then large particles of Co_(3)O_(4)-700 distributed disorderly. The increase in pyrolysis temperature also led to the increase in the particle size from 16.2 nm(400 ℃)to 46.2 nm(700 ℃). According to Co_(3)O_(4),Co3+ species were considered as the active sites for catalytic oxidation,so XPS was used to get the information of catalyst chemical states,and it was found that the ratio of Co3+/Co2+ decreased with the increase in the pyrolysis temperature. The ratio of Co3+/Co2+ was up to 1.41 on Co_(3)O_(4)-400 while it decreased to 0.99 on Co_(3)O_(4)-700. The blue shifts of Raman band further confirmed the decrease in the oxygen vacancy. Compared with the H_(2)-TPR and O_(2)-TPD and profiles of Co_(3)O_(4)-400,the shifts of reduction peaks to higher temperature and the decrease in O_(2) desorption peak area were found on Co_(3)O_(4)-700,which illustrated the loss in redox property caused by the enhancement in pyrolysis temperature. Meanwhile,soot-TPR further demonstrated the lower activity of oxygen species on Co_(3)O_(4)-700,for soot reduced oxygen usually occurred at higher temperature. The experiments results showed that the high content of Co3+-O and surface oxygen vacancies on Co_(3)O_(4)-400 accelerated O_(2) adsorption and activation. In contrast,the increase in pyrolysis temperature decreased the Co3+-O concentration and oxygen vacancies,then the ability in oxygen activation was inhibited.