【作者】 刘强；

【导师】 钟秦；

【作者基本信息】 南京理工大学 ， 化学工程（专业学位）， 2021， 硕士

【摘要】 近年来,随着化石资源的不断消耗和二氧化碳（CO₂）排放量逐年增长,能源和环境问题受到了广泛关注。将CO₂加氢直接合成低碳烯烃具有良好的应用前景,不仅可以实现CO₂减排及CO₂转化,还可以缓解能源危机和温室效应。铁基催化剂是常用的CO₂加氢制低碳烯烃催化剂,通过添加过渡金属、碱金属等助剂和载体,能有效地促进低碳烯烃的合成,但其促进机制和反应机理还有待进一步深入研究。同时,由于催化产物中的C₂-C₄烃的选择性受安德森-舒尔茨-弗洛里（ASF）分布限制,通过传统的改性方式难以进一步提高铁基催化剂的低碳烯烃收率。针对这些问题,本论文以提高铁基催化剂制低碳烯烃的效率为目的,开展了氧化锆（ZrO₂）载体制备、钾（K）助剂和SAPO-34分子筛引入研究。主要内容如下:首先,采用水热法、沉淀法、溶胶凝胶法和直接煅烧法制备了ZrO₂,并将其作为载体,采用浸渍法得到FeCoK/ZrO₂催化剂,研究了载体制备方法对CO₂催化加氢反应性能的影响,结果表明,直接煅烧法、水热法和沉淀法制备的ZrO₂主要为单斜晶型,而溶胶凝胶法制备的ZrO₂含单斜和四方两种晶型。活性测试结果显示,溶胶凝胶法制备的混合晶型ZrO₂不利于CO₂的吸附,反应活性较低。同时,以直接煅烧法得到的ZrO₂为载体制备了FeCo/ZrO₂和FeCoK/ZrO₂催化剂,考察了K含量对催化CO₂加氢反应活性的影响,结果表明,K的加入增加了铁物种的电子云密度,增强了CO₂在Fe物种表面的吸附,促进了碳化铁（χ-Fe₅C₂）的形成,优化了CO₂吸附活化的路径,从而提高了CO₂的转化率和低碳烯烃选择性,使低碳烯烃的时空收率（STY）由0.013 mmol·g_cat^-1·h^-1提高到4.11 mmol·g_cat^-1·h^-1。其次,采用沉淀法和浸渍法制备了FeZnK催化剂,并应用双层床、颗粒堆积和物理混合三种结合方式制备出FeZnK/SAPO-34催化剂,考察了上述三种结合方式对CO₂加氢反应性能的影响,结果表明,由于物理混合的催化剂中FeZnK和SAPO-34接触紧密,导致K在高温下与SAPO-34发生离子交换,降低了FeZnK的碱性和SAPO-34的酸性,从而抑制了χ-Fe₅C₂的生成,低碳烯烃收率下降。颗粒堆积的催化剂中FeZnK和SAPO-34仅有少量的离子交换,两者的酸碱性几乎不受影响。同时,由于SAPO-34对长链烃的裂化能力,FeZnK催化转化CO₂的产物中烃类的ASF分布被打破,低碳烯烃的STY由4.29 mmol·g_cat^-1·h^-1提高至5.05 mmol·g_cat^-1·h^-1,且催化剂表现出良好的反应稳定性能。最后,采用沉淀法和浸渍法制备出FeCoK、FeMnK和FeZnK催化剂,并应用颗粒堆积的方法制备了Fe MK/SAPO-34（M=Co,Mn和Zn）催化剂。催化反应性能测试结果显示,由于SAPO-34对烃类的催化裂化作用,乙烯的选择性明显提高,三种过渡金属对Fe MK/SAPO-34（M=Co,Mn和Zn）催化剂反应性能促进作用的大小顺序为Zn>Co>Mn。同时,考察了不同酸性的SAPO-34对FeZnK/SAPO-34反应性能的影响,结果表明,SAPO-34酸性的提高有利于长链烃裂化为短链烃。但过高的酸性会加剧FeZnK中K与SAPO-34发生离子交换,FeZnK的碱性降低,烯烃的二次加氢加剧。因此,适中酸性的SAPO-34更有利于低碳烯烃的产生。更多还原

【Abstract】 In recent years,with the consumption of fossil resources and the massive emission of carbon dioxide（CO₂）,more and more attention has been paid to greenhouse gas and increasing energy demand.Direct synthesis of light olefins by hydrogenation of CO₂ has a broad prospect,it can not only achieve CO₂ emission reduction and CO₂ conversion,but also alleviate energy crisis and greenhouse effect.Iron-based catalysts has been widely used for CO₂ hydrogenation to synthesis light olefins.The synthesis of light olefins could be effectively promoted by adding transition metals,alkali metals and supports on iron oxide,but its promotion mechanism and reaction mechanism need to be studied for further.At the same time,since the selectivity of C₂-C₄ hydrocarbons in the catalytic product follow by the Anderson-Schultz-Flory（ASF）distribution,it is difficult to further increase the yield of light olefins of the iron-based catalysts through traditional modification methods.For these problems,the aim of this paper is improving the efficiency of iron-based catalysts for the producing of light olefins,and focusing on the preparation of the carriers of zirconia（ZrO₂）,potassium（K）promoter and the introduction of SAPO-34 molecular sieves.The main contents list as follows:First,ZrO₂ was prepared by hydrothermal,precipitation,sol-gel and direct calcination methods,and FeCoK/ZrO₂ catalyst was obtained by impregnation and using it as a support.The effect of CO₂ hydrogenation performance for support with different preparation method was studied.The results show that the mainly crystal form of ZrO₂ prepared by direct calcination,hydrothermal and precipitation methods is monoclinic,while ZrO₂ prepared by sol-gel method contains both monoclinic and tetragonal crystals.The activity test results show that the mixed crystal ZrO₂ prepared by the sol-gel method is not beneficial to the CO₂ adsorption,and the reaction activity is low.At the same time,FeCo/ZrO₂ and FeCoK/ZrO₂ catalysts were prepared with ZrO₂ obtained by direct calcination method as the support.The influence of K content on the catalytic activity of CO₂ hydrogenation reaction was investigated.The results showed that the addition of K increased the electron cloud density of iron species.Enhances the adsorption of CO₂ on the surface of Fe species,promotes the formation of iron carbide（χ-Fe₅C₂）,and optimizes the path of CO₂ adsorption and activation,thereby increasing CO₂ conversion and the selectivity of light olefins.And the space-time yield（STY）increased from 0.013 mmol·g_cat^-1·h^-1 to 4.11 mmol·g_cat^-1·h^-1.Secondly,the FeZnK catalyst was prepared by the precipitation and the impregnation method,and the FeZnK/SAPO-34 catalyst was prepared by the three integrated methods of dual-bed,granule stacking and physical mixing.The performance of CO₂ hydrogenation reaction for the above three integrated methods was investigated.The results show that the close contact between FeZnK and SAPO-34 in the physically mixed catalyst,leading to K ion exchanges with SAPO-34 at high temperature,which reduces the alkalinity of FeZnK and the acidity of SAPO-34,thereby suppressing the formation ofχ-Fe₅C₂,reduces the yield of low-carbon olefins.A trace of ion exchange was detected in granule-stacking catalyst,and the acidity and alkalinity have almost no change.At the same time,due to the cracking ability of SAPO-34,the ASF distribution of hydrocarbons in the products of FeZnK was broken,and the STY of light olefins increased from 4.29 mmol·g_cat^-1·h^-1 to 5.05 mmol·g_cat^-1·h^-1,and the catalyst shows good reaction stability.Finally,FeCoK,FeMnK and FeZnK catalysts were prepared by precipitation and impreganation method,and FeMK/SAPO-34（M=Co,Mn and Zn）catalysts were prepared by granule-stacking method.The catalytic reaction performance test results show that due to the cracking effect of hydrocarbons by SAPO-34,the selectivity of ethylene is significantly improved,and the order of the promotion effect of the reaction performance for three transition metals on FeMK/SAPO-34（M=Co,Mn and Zn）catalysts is Zn>Co>Mn.At the same time,the effect of SAPO-34 with different acidity on the reaction performance of FeZnK/SAPO-34was investigated.The results showed that the increase of SAPO-34 acidity is beneficial to the cracking of long-chain hydrocarbons into short-chain hydrocarbons.However,excessive acidity will aggravate the ion exchange between K in FeZnK and SAPO-34,reduce the alkalinity of FeZnK,and increase the secondary hydrogenation of olefins.Therefore,moderately acidic SAPO-34 is more conducive to the production of light olefins.更多还原