助剂对CO₂加氢合成CH₃OH催化剂性能影响的研究

【作者】 刘艳；

【导师】 樊君；

【作者基本信息】 西北大学 ， 化学工艺， 2015， 硕士

【摘要】 当今社会科技迅猛发展,给环境造成了巨大的压力和负担,导致了越来越严重的温室效应,对整个社会造成了不可遏制的影响。为降低温室效应,高效CO2捕集技术的开发成为研究重点。除去常规的CO2封存和捕集技术,研究人员更注重将CO2用作工业反应的原料气,用于制备甲醇、甲醛等有机物。甲醇是工业中有机物的基础原料之一,利用CO2制备甲醇既降低环境的压力,又能合成工业所需的基础原料,非常具有研究意义。为了进一步研究C02和H2制备甲醇,本文从以下几个方面进行了研究：首先,经筛选,柠檬酸-凝胶溶胶法制备催化剂的纯度较高,颗粒均匀细小。故采用该法制备CuO/ZnO/Al2O3/CeO2四元催化剂,考察掺杂助剂Ce后催化剂的活性,并研究了不同A1-Ce摩尔比下催化剂的不同性质及结构变化。经测试发现：随着A1-Ce摩尔比的增加,CO2的转化率、甲醇选择性以及收率均呈现先增加后减小的趋势。最终可知,A1-Ce摩尔比为1：1时,催化剂的活性最高。同时考察不同反应条件(温度、压力和空速)对催化剂活性的影响。随着温度的升高,甲醇收率先升高后降低；压力越高,甲醇收率越高；空速对甲醇收率影响不大。综合可得最优反应条件为：反应温度493 K,反应压力3 MPa, n(H2):n(CO2)=3:1,空速4800 mL·h-1·gcat-1。此条件下A1-Ce摩尔比为1：1催化剂的CO2转化率为9.9%,甲醇选择性为60.8%,甲醇收率为5.9%。最后对催化剂进行稳定性测试。通过BET、XRD、H2-TPR和SEM等表征手段研究催化剂的结构,并结合活性评价对催化剂结构进行分析,可知不同A1-Ce摩尔比制得的催化剂的颗粒均匀,且有较大的比表面积和孔容,不同A1-Ce摩尔比的催化剂对CuO还原的难易程度不同,催化剂的A1-Ce摩尔比为1：1时所得的催化剂的H2还原温度最低。钙钛矿型催化剂作为一种新型结构催化剂,也可应用于CO2加氢制甲醇反应中。采用柠檬酸-凝胶溶胶法制备La-M-Cu-Zn-O(M=Y, Ce, Mg, Zr)催化剂,添加助剂M部分替换La-Cu-Zn-O催化剂中的La元素,考察添加助剂后催化剂的催化活性,并用BET、XRD、H2-TPR和SEM表征催化剂。考察不同反应条件对催化剂活性的影响,对催化剂的稳定性进行评价。结果显示：在温度533K、压力为3Mpa、空速是3600 mL·h-1·gcat-1的条件下,添加不同助剂M所得到催化剂活性均有提高。添加zr之后催化剂LZCZO-8273的CO2转化率和甲醇收率最高,分别是11.8%和6.69%；添加Mg制得的LMCZO-8273催化剂甲醇选择性最高,为65.7%,但C02转化率和甲醇收率较低；综合可得LZCZO-8273催化剂的性能较好。添加助剂之后催化剂颗粒变小,分布均匀,有利于提高甲醇的选择性。H2还原温度也相对于LCZO-173的还原温度降低了。在稳定性测试阶段,CO2转换率和甲醇收率均无明显波动。更多还原

【Abstract】 With the rapid development of science and technology in current society, it has created great pressure and burden to the environment, leading to the greenhouse effect. While the greenhouse effect was becoming more and more serious, it had an unstoppable impact on the whole society. In order to lighten this effect, the main emphasis of science and technology had focused on the development of efficient CO2 capture technology. Apart from the conventional CO2 sequestration and capture technology, researchers paid more attention to CO2 as industrial raw gas, which was used for the preparation of methanol, formaldehyde and other organic, full of great significance.First of all, after all kinds of sifts, catalysts prepared by acid sol-gel method had much advantages including high purity and tiny particles. Therefore, the CuO/ZnO/Al2O3/CeO2 quaternary composite catalysts were prepared by acid sol-gel method and the catalyst activity was studied after adding Ce as additive in catalysts. Also, the properties and structural changes at different mole ratio of Al-Ce had also been studied. After tests, the results showed that CO2 conversion, methanol selectivity and yield increased first and then decreased with the increase of mole ratio of Al-Ce. Finally, we got the highest activity of catalysts while the mole ratio of Al-Ce is 1:1. At the same time, we studied the changes on catalyst activity in different reaction conditions(temperature、pressure、and space velocity). Methanol yield rose first and then dropped with the increase of temperature; the higher pressure was the larger methanol yield was; space velocity had little effect on methanol yield. The results showed that the best catalytic effect achieved at the reaction temperature of 493 K, pressure of 3 MPa, and the space velocity of 4800 mL·h-1·gcat-1. And CO2 conversion, methanol selectivity and yield were 9.9%, 60.8% and 5.9%, respectively. Finally, the stability of CuO/ZnO/Al2O3/CeO2 quaternary composite catalyst was tested.The catalysts were characterized by BET, XRD, H2-TPR and SEM techniques to study the structure of the catalyst in this paper, and catalyst structure was analyzed along with the activity tests. The results showed that the catalysts at different mole ratio of Al-Ce were all particle uniformity、larger specific surface area and bigger pore volume. Catalysts with different Al-Ce molar ratio initiated diversity of CuO reduction. When the mole ratio Al-Ce was 1:1, H2 reduction temperature was the lowest.Secondly, as a new structure catalyst, perovskite catalysts could also be used in the CO2 hydrogenation to methanol. La-M-Cu-Zn-O (M=Y, Ce, Mg, Zr) catalysts were prepared by acid sol-gel method. M additive content was added to in La-Cu-Zn-O catalyst to replace partial La elements. The catalysts were characterized by XRD, SEM, BET and H2-TPR techniques along with catalyst evaluation to study the performance. And then we studied the effect of different reaction conditions on the activity of catalyst. Finally, the stability of the catalyst was estimated.Results displayed that activity of catalyst prepared by adding M additives entirely increased at temperature of 533 K, pressure of 3 MPa, and space velocity of 3600 mL·h-1·gcat-1. LZCZO-8273 catalyst that was added Zr additive content had the highest CO2 conversion and methanol yield, which were 11.8% and 6.69%, respectively. Methanol selectivity of LMCZO-8273 catalyst prepared by adding Mg additive content was the highest, which was 65.7%. After all, LZCZO-8273 catalyst had better activity. Catalysts prepared by adding additives had smaller particles and good catalyst distribution, which improved the selectivity of methanol. H2 reduction temperature of the catalyst decreased compared to that of the LCZO-173 catalyst. Through stability test, CO2 conversion and methanol yield had no obvious fluctuation.更多还原