【作者】 赵云鹏；

【导师】 郑钟植； 孙德智；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2013， 博士

【摘要】 大量排放的二氧化碳造成了全球温室效应和环境污染，研究CO₂的减排与利用已经成为世界性关注的热点和急需解决的问题。CO₂加氢合成甲醇是合理利用二氧化碳的有效途径之一，甲醇是一种极其重要的基础有机化工原料，又是一种很有发展前途的新型环保清洁优质燃料。CO₂加氢合成甲醇为能源结构的战略调整提供了新途径，对解决日益严重的环境与能源问题具有重要的意义。CO₂加氢合成甲醇通常采用的催化剂制备方法存在CO₂转化率低，甲醇选择性不高的问题。针对这些问题，提出了采用添加十六烷基三甲基溴化铵（CTAB）表面活性剂并流浆态共沉淀法制备CuO-ZnO/TiO₂催化剂，有效改善了催化剂的结构与催化性能。采用添加表面活性剂并流浆态共沉淀法、添加表面活性剂分步沉淀法、并流浆态共沉淀法及浸渍法制备了CuO-ZnO/TiO₂催化剂，利用BET、XRD、SEM、EDS、H₂-TPR、H₂-TPD、CO₂-TPD等方法对催化剂的物理与化学性能进行了表征，研究了不同的制备方法对CuO-ZnO/TiO₂催化剂性能的影响，通过固定床反应器对CO₂加氢合成甲醇CuO-ZnO/TiO₂催化剂的催化性能进行了评价。研究结果表明，不同方法制备的CuO-ZnO/TiO₂催化剂均为介孔材料，沉淀法制备的CuO-ZnO/TiO₂催化剂BET比表面积和孔容大于浸渍法制备的催化剂，CuO和ZnO的分散性好。TiO₂载体起到阻止CuO晶粒长大和促进CuO分散的作用。沉淀法中以添加表面活性剂并流浆态共沉淀法制备的CuO-ZnO/TiO₂催化剂上CuO的还原温度最低，催化活性最好。浸渍法制备的催化剂上CuO的还原温度最高，催化活性低。H₂-TPD表明高温强吸附态下H₂的脱附峰面积大，催化剂表面上吸附更多的活化H₂，促进了CO₂加氢合成甲醇的反应。CO₂-TPD表明中等强度的CO₂吸附中心与二氧化碳加氢合成甲醇的效果密切相关。不同方法制备的CuO-ZnO/TiO₂催化剂活性及CH3OH选择性由高到低的顺序依次为：添加表面活性剂并流浆态共沉淀法＞添加表面活性剂分步沉淀法＞并流浆态共沉淀法＞浸渍法，添加表面活性剂有效地改善了CuO-ZnO/TiO₂催化剂的催化性能。添加表面活性剂并流浆态共沉淀法制备的CuO-ZnO/TiO₂催化剂上CO₂加氢合成甲醇反应的催化性能最好。在反应压力2.5MPa、反应空速2100h-1、反应温度230℃、H₂和CO₂摩尔比3:1、反应时间4h的条件下，CO₂的转化率为13.26%，CH3OH的选择性为23.95%，CH3OH的产率最大为3.18%。添加助剂对CO₂加氢合成甲醇催化剂的结构与性能具有重要影响，研究了在CuO-ZnO/TiO₂催化剂中分别添加ZrO₂、Al2O3及MnOχ助剂，采用添加CTAB表面活性剂并流浆态共沉淀法制备了CuO-ZnO-ZrO₂/TiO₂、CuO-ZnO-Al2O3/TiO₂及CuO-ZnO-MnOχ/TiO₂催化剂，利用BET、XRD、SEM、EDS、H₂-TPR、H₂-TPD、CO₂-TPD等方法对各催化剂的结构与化学性能进行了表征，研究了添加不同助剂及改变添加的ZrO₂助剂含量对CuO-ZnO/TiO₂催化剂性能的影响。通过XRD、XPS、H₂-TPD、CO₂-TPD、DRIFT等方法探讨了CuO-ZnO-ZrO₂/TiO₂催化剂上CO₂加氢合成甲醇的反应机理。研究结果表明，添加不同助剂均增加了CuO-ZnO/TiO₂催化剂的比表面积和孔容，添加MnOχ使CuO-ZnO/TiO₂催化剂上CuO的还原温度升高，吸附H₂的浓度降低，催化活性下降。添加ZrO₂或Al2O3助剂均降低了CuO的还原温度，吸附H₂和CO₂的能力增强，促进了甲醇的合成。含不同助剂的CuO-ZnO/TiO₂催化剂中，添加ZrO₂助剂的CuO-ZnO-ZrO₂/TiO₂催化剂的催化性能最好，在反应压力2.5MPa、反应空速2100h-1、反应温度230℃、H₂和CO₂摩尔比3:1、反应时间4h的条件下，CO₂的转化率为18.24%，CH3OH的选择性为31.52%，CH3OH的产率最大为5.75%。ZrO₂助剂的含量对CuO-ZnO/TiO₂催化剂的结构与性能具有显著影响。随着ZrO₂助剂含量的增加，催化剂的比表面积和孔容增大，孔径分布变均匀。ZrO₂促进了催化剂上CuO和ZnO的分散，降低了CuO的还原温度，提高了催化剂的活性。H₂-TPD表明增加催化剂中ZrO₂含量促进了对H₂的强吸附，催化剂表面上吸附H₂的浓度高，并具有储氢的作用，提高了CO₂加氢合成甲醇反应的速率。CO₂-TPD表明ZrO₂对促进CO₂的吸附与活化具有显著作用。ZrO₂助剂含量增加，提高了催化剂的催化性能。CuO-ZnO-ZrO₂/TiO₂催化剂上的CuO还原后为零价金属铜，Cu⁰是H₂吸附与解离的活性中心，ZnO和ZrO₂是CO₂的吸附活性中心。甲醇合成机理是CuO-ZnO-ZrO₂/TiO₂催化剂上双活性中心分别吸附活化H₂和CO₂，以CO₂为碳源直接加氢合成甲醇的反应。更多还原

【Abstract】 A large amount of carbon dioxide emission led to global greenhouse effect andenvironmental pollution. Research of carbon dioxide emission reduction andutilization is of focus and urgent issues in the world. Methanol synthesis by carbondioxide hydrogenation is one of approaches of carbon dioxide utilization. Methanolis considered an important raw material of fundamental organic chemical industryand a new-type environmental protection clean fuels. Carbon dioxide hydrogenationto methanol is a new pathway for strategic adjustment of energy structure, and it isimportant significance to solve the increasingly environmental pollution and energyquestions.In the process of carbon dioxide hydrogenation to methanol, the existingproblems of the general preparation methods of catalysts are lower to carbon dioxideconversion and methanol selectivity. In regard to these problems, CuO-ZnO/TiO₂catalysts were prepared by a novel parallel-slurry-mixing-precipitation methodcombined with addition of cetyltrimethylammonium bromide （CTAB） surfactant.Structure and catalytic performance of catalysts were improved effectively.CuO-ZnO/TiO₂catalysts were prepared by parallel-slurry-mixing-precipitationmethod combined with addition of surfactant, two-step precipitation methodcombined with addition of surfactant, parallel-slurry-mixing-precipitation andimpregnation method, respectively. Characterizations of physical and chemicalproperties of the catalysts were investigated by BET, XRD, SEM, EDS, H₂-TPR,H₂-TPD and CO₂-TPD. The effects of different preparation methods on catalyticperformances of CuO-ZnO/TiO₂catalysts were studied. The catalytic performancesof CuO-ZnO/TiO₂catalysts for methanol synthesis from CO₂hydrogenation wereevaluated by fixed bed reactor.The research results show that CuO-ZnO/TiO₂catalysts of different preparationmethods are mesoporous materials. BET specific surface area and pore volume forthe CuO-ZnO/TiO₂catalysts of precipitation methods are greater than that ofimpregnation method, and dispersion of CuO and ZnO is better. TiO₂preventedgrowth of CuO crystal particles and promoted the dispersion of CuO species. In theprecipitation methods, CuO reduction temperature of CuO-ZnO/TiO₂catalyst ofparallel-slurry-precipitation method combined with addition of surfactant is lowest,and its reduction is easiest. CuO reduction temperature of that of impregnationmethod is highest, and its catalytic activity is lowest. H₂-TPD showed that hydrogendesorption peak area was large at high temperature and strong adsorption state, andactive hydrogen molecules on catalyst surface were more and more, and methanol synthesis from CO₂hydrogenation was promoted. CO₂-TPD revealed that CO₂adsorption center of moderate intensity was closely related to methanol synthesisfrom CO₂hydrogenation. From high to low, the activity and methanol selectivity ofCuO-ZnO/TiO₂catalysts of different preparation methods wasparallel-slurry-mixing-precipitation method combined with addition of surfactant,two-step precipitation method combined with addition of surfactant,parallel-slurry-mixing-precipitation and impregnation method. Addition ofsurfactant improved effectively catalytic performances of CuO-ZnO/TiO₂catalysts.CuO-ZnO/TiO₂catalyst of parallel-slurry-precipitation method combined withaddition of surfactant for methanol synthesis from CO₂hydrogenation was best.Under the conditions of reaction pressure of2.5MPa, space velocity of2100h-1,reaction temperature of230℃, H₂/CO₂molar ratio of3:1and reaction time4h,carbon dioxide conversion and methanol selectivity and maximum of methanol yieldwere13.26%,23.95%and3.18%, respectively.Additives of catalysts used in methanol synthesis from carbon dioxidehydrogenation are important effect on structure and performance of catalyst.CuO-ZnO/TiO₂catalyst added ZrO₂, Al2O3and MnOχ, respectively.CuO-ZnO-ZrO₂/TiO₂, CuO-ZnO-Al2O3/TiO₂and CuO-ZnO-MnOχ/TiO₂catalystswere prepared by parallel-slurry-mixing-precipitation method combined withaddition of CTAB surfactant. The structure characterization and chemical propertiesof the catalysts were investigated by BET, XRD, SEM, EDS, H₂-TPR, H₂-TPD,CO₂-TPD. The effects of different promoters and ZrO₂content on catalyticperformance of CuO-ZnO/TiO₂catalyst were studied. In the presence ofCuO-ZnO-ZrO₂/TiO₂catalyst, reaction mechanism of carbon dioxide hydrogenationto methanol was discussed by XRD, XPS, H₂-TPD, CO₂-TPD and DRIFT.The research results show that addition of different promoters increasedspecific surface area and pore volume for the CuO-ZnO/TiO₂catalysts. The additionof MnOχon CuO-ZnO/TiO₂catalyst increased the reduction temperature of CuO,and decreased adsorptive hydrogen concentration and catalytic activity. AddingZrO₂or Al2O3promoter decreased the reduction temperature of CuO, enhancedcapacity of H₂and CO₂adsorption, and promoted methanol synthesis. In theCuO-ZnO/TiO₂catalysts containing different promoter, CuO-ZnO-ZrO₂/TiO₂catalyst exhibited an optimal catalytic performance. Under the conditions ofreaction pressure of2.5MPa, space velocity of2100h-1, reaction temperature of230℃, H₂/CO₂molar ratio of3:1and reaction time4h, carbon dioxide conversionand methanol selectivity and maximum of methanol yield were18.24%,31.52%and5.75%, respectively.ZrO₂content is important effect on the structure and performance ofCuO-ZnO/TiO₂catalysts. Along with the increase of ZrO₂content, specific surface areas and pore volume of the catalysts increase, and pore size distribution isconcentrated. ZrO₂promoted the dispersion of CuO and ZnO species and decreasedthe reduction temperature of CuO, and enhanced catalyst activity. H₂-TPD showedthat increasing ZrO₂content of catalysts promoted strong adsorption of hydrogenand adsorptive hydrogen of higher concentration on catalyst surface, and possessedfunction of hydrogen storage and enhanced reaction rate of CO₂hydrogenation.CO₂-TPD revealed that ZrO₂improved CO₂adsorption and activation. IncreasingZrO₂content of catalysts enhanced catalytic performance.On the CuO-ZnO-ZrO₂/TiO₂catalyst, CuO being reduced to Cu species are theactive sites of H₂adsorption and dissociation. ZnO and ZrO₂species are the activesites of CO₂adsorption. The dual-site reaction mechanism of adsorption andactivation for H₂and CO₂is reasonable for the directly synthesis methanol by CO₂hydrogenation on the CuO-ZnO-ZrO₂/TiO₂catalyst.更多还原