石墨烯为载体的铜基催化剂应用于二氧化碳加氢合成甲醇反应

发布时间：2018-10-09 13:52

【摘要】：二氧化碳加氢合成甲醇反应是最具潜力的二氧化碳利用研究方向,其中该反应所用的铜基催化剂的低活性、低甲醇选择性和稳定性差是影响工业化应用的关键问题。本文采用石墨烯为载体,利用石墨烯载体的大比表面积和高H2和C02吸附性能,制备石墨烯为载体的铜基催化剂,从而提高催化剂的活性、选择性和稳定性。研究结果对提高二氧化碳加氢合成甲醇反应催化剂的性能和未来工业化应用具有重要的指导意义。本文首先建立二氧化碳加氢合成甲醇反应过程的热力学模型,通过Matlab模拟计算了不同温度、压力、H2/C02比对二氧化碳转化率和甲醇选择性的影响。计算结果显示,低温高压有利于生成目标产物甲醇。将计算值与已有实验值进行比较,在相同实验条件下,二氧化碳转化率仍有10%的提高空间,证明目前该反应的限制不在热力学而在动力学,故催化剂的开发是研究的重点。其次,采用共沉淀法制备CuO-ZnO-ZrO2-Al2O3/rGO (CZZA/rGO)催化剂和CuO-ZnO-ZrO2-Al2O3 (CZZA)催化剂,用于二氧化碳加氢合成甲醇反应。采用BET、XRD、SEM、H2-TPR、H2-TPD及CO2-TPD等进行表征,并在固定床反应器上对其进行催化活性评价。通过研究反应温度、反应压力和空速对二氧化碳加氢合成甲醇反应催化剂催化性能的影响,确定本实验最佳反应条件为513 K,2 MPa和6075 h-1。与此同时,对比了不同催化剂CZZA/rGO和CZZA的结构特性、还原性能、吸附性能及催化性能。结果表明：CZZA/rGO催化剂拥有大的比表面积125.56 m2·g-1,较强的还原性以及较好的H2和CO2吸附性能。与CZZA催化剂相比,在相同反应条件下,随着rGO载体的加入,CZZA/rGO催化剂的二氧化碳转化率和甲醇收率分别增加了11.7%和18.1%,且与二氧化碳转化率热力学计算值相差8%。与此同时,CZZA/rGO催化剂的甲醇TOF值为0.0687 s-1,远远大于CZZA催化剂的甲醇TOF值0.0083 s-1,证明CZZA/rGO催化剂的活性有很大提高。再次,采用尿素水解法制备CuO-ZnO/rGO(CZ/rGO)和CuO-ZnO/Al2O3(CZA)催化剂,改变催化剂制备条件,得到的催化剂结合BET、XRD、SEM、H2-TPR、 H2-TPD和CO2-TPD等表征手段,采用固定床反应器在优选反应条件下评价催化剂性能。考察了不同水解温度、活性组分含量及不同载体对催化剂催化性能的影响。结果表明,相比于Al2O3载体,rGO为载体的催化剂拥有更高的还原性能及H2和CO2吸附性能,且随着活性组分含量减小,即载体量增加,H2和CO2吸附量增加,催化剂的活性组分能更多的保持在Cu0和Cu+价态,提高了催化剂的还原性能。尿素水解法制备的25%CZ/75%rGO催化剂拥有最高的二氧化碳转化率8.4%和甲醇收率7.28%,且25%CZ/75%rGO催化剂的甲醇TOF值最高达到0.0248 s-1,而CZA催化剂的甲醇TOF值仅为0.0029 s-1,证明rGO为载体的催化剂活性高。最后研究考察了催化剂的吸附性能与还原性能及催化性能的关系。研究发现,低反应温度下H2和CO2吸附性能影响二氧化碳转化率,而催化剂的总H2吸附性能影响催化剂的甲醇选择性。以rGO为载体的催化剂拥有很强的H2吸附能力,其中,25%CZ/75%rG0催化剂和50%CZ/50%rGO催化剂的H2吸附量是CZA催化剂的10倍,高的H2吸附量为催化剂提供还原氛围,使高含量载体rGO的催化剂拥有Cu0或Cu+活性中心,更有利于加氢反应的进行,从而提高催化剂的甲醇选择性,甲醇选择性在90%左右。故催化剂的H2和CO2吸附性能影响催化剂的还原性能和催化性能。
[Abstract]:The carbon dioxide hydrosynthesis methanol reaction is the most potential carbon dioxide utilization research direction, in which the low activity, low methanol selectivity and poor stability of the copper-based catalyst used in the reaction are the key problems affecting the industrialization application. In this paper, graphene is used as a carrier to prepare a copper-based catalyst with graphene as a carrier by utilizing the large specific surface area and high H2 and C02 adsorption properties of the graphene carrier, thereby improving the activity, selectivity and stability of the catalyst. The results are of great guiding significance to improve the performance and future industrial application of methanol synthesis catalyst. In this paper, the thermodynamic model of carbon dioxide hydrosynthesis methanol synthesis process was established, and the effect of different temperature, pressure, H2/ C02 ratio on the conversion of carbon dioxide and methanol selectivity was simulated by Matlab. The results show that low temperature high pressure is beneficial to the generation of target product methanol. Comparing the calculated value with the existing experimental value, under the same experimental conditions, the carbon dioxide conversion rate still has 10% improvement space, which proves that the current limit of the reaction is not in the thermodynamics, so the development of the catalyst is the focus of the research. CuO-ZnO-ZrO2-Al2O3/ rGO (CZZA/ rGO) catalyst and CuO-ZnO-ZrO2-Al2O3 (CZZA) catalyst were prepared by co-precipitation method. BET, XRD, SEM, H2-TPR, H2-TPD and CO2-TPD were used to characterize the catalytic activity. By studying the effect of reaction temperature, reaction pressure and space velocity on the catalytic performance of methanol synthesis catalyst, the optimum reaction conditions were 513K, 2MPa and 6075h-1. At the same time, the structural characteristics, reducibility, adsorption performance and catalytic performance of different catalysts CZZA/ rGO and CZZA were compared. The results show that the CZZA/ rGO catalyst has a large specific surface area of 125. 56 m2 路 g-1, stronger reducibility and better H2 and CO2 adsorption properties. Compared with CZZA catalyst, under the same reaction conditions, with the addition of rGO carrier, the conversion of carbon dioxide and methanol yield of CZZA/ rGO catalyst increased by 11. 7% and 18. 1%, respectively, and the thermodynamic calculation value of carbon dioxide conversion was 8%. At the same time, the methanol TOF value of CZZA/ rGO catalyst is 0. 0687 s-1, which is much larger than that of CZZA catalyst, and the methanol TOF value is 0. 0083 s-1. It is proved that the activity of CZZA/ rGO catalyst is greatly improved. CuO-ZnO/ rGO (CZ/ rGO) and CuO-ZnO/ Al2O3 (CZA) catalysts were prepared by urea hydrolysis, and the catalyst preparation conditions were changed. The catalysts obtained were characterized by BET, XRD, SEM, H2-TPR, H2-TPD and CO2-TPD. The effects of different hydrolysis temperature, content of active components and different carrier on the catalytic performance of catalyst were investigated. The results show that the catalyst with rGO as carrier has higher reducing energy and H2 and CO2 adsorption properties compared with Al2O3 carrier, and as the content of active component decreases, that is, the amount of carrier increases, the adsorption amount of H2 and CO2 increases, the active component of catalyst can be kept at Cu0 and Cu + valence state more, and the reducing energy of the catalyst is improved. The 25% CZ/ 75% rGO catalyst prepared by the urea hydrolysis method has the highest carbon dioxide conversion rate of 8. 4% and the methanol yield of 7.28%, and the methanol TOF value of the 25% CZ/ 75% rGO catalyst is up to 0.0248s-1, while the methanol TOF value of the CZA catalyst is only 0. 0029s-1, and the catalyst activity of the rGO as the carrier is high. The relationship between adsorption performance and reducibility and catalytic performance of catalyst was investigated. It was found that the adsorption properties of H2 and CO2 at low reaction temperature affect the conversion of carbon dioxide, and the total H2 adsorption performance of the catalyst affects the methanol selectivity of the catalyst. the catalyst with rGO as carrier has strong H2 adsorption capacity, wherein the H2 adsorption amount of 25% CZ/ 75% rG0 catalyst and 50% CZ/ 50% rGO catalyst is 10 times of CZA catalyst, the high H2 adsorption amount provides a reducing atmosphere for the catalyst, and the catalyst with high content carrier rGO has Cu0 or Cu + active center, more favorable hydrogenation reaction is carried out, so that the methanol selectivity of the catalyst is improved, and the selectivity of methanol is about 90 percent. The H2 and CO2 adsorption properties of the catalyst affect the reducibility and catalytic performance of the catalyst.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ223.121;O643.36

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