预处理过程对钴基费托催化剂结构及性能的影响
发布时间：2018-12-25 15:44
【摘要】：费托合成(FTS)是将合成气(H_2/CO)转化为优质清洁能源和高附加值化工产品的重要途径,通常采用钴基催化剂和铁基催化剂。相比于铁基催化剂,钴基费托催化剂具有高转化率、不易失活和低水煤气变换活性的优点。虽然FTS已经研究了很长时间,但是在如何提高催化剂性能和弄清楚费托反应的机理方面还是有很大的提升空间。一般而言,催化剂的活性与催化的粒子大小存在重要的联系,如果能够使烧结的催化剂颗粒进行再分散从而重新获得活性,这将对理论研究和实际工业应用都大有裨益。本文通过浸渍法制备了Co/SiO_2催化剂,对催化剂进行还原氧化还原(ROR)和还原碳化还原(RCR)处理。通过XRD、BET、TEM和H_2-TPR等表征手段研究预处理过程中催化剂结构的变化;采用固定床反应器进行催化剂评价,研究不同预处理过程对催化剂性能的影响。主要得到以下结论:1、通过使用不同钴的前驱体制备了具有不同初始粒子大小的催化剂,对催化剂进行还原、还原氧化(RO)和还原氧化还原(ROR)处理。结果发现,这些预处理过程对催化剂的物理结构没有太大的影响;但是催化剂的颗粒尺寸发生了很明显的变化。当进行RO处理时,催化剂的颗粒明显变小,说明RO处理可以使催化剂进一步分散。进行ROR处理得到的催化剂颗粒要比直接还原的催化剂颗粒小,而且这种颗粒尺寸的变化程度与催化剂初始颗粒大小有关:催化剂初始颗粒越大,ROR处理后催化剂颗粒减少的程度越大。例如使用氯化钴前驱体制备的催化剂焙烧后颗粒大小为35.2 nm,经过ROR处理后颗粒减小到24.7 nm。2、通过对催化剂在氧气和水蒸气中进行氧化处理,研究ROR过程中的氧化过程对催化剂结构和性能的影响。水蒸气通过鼓泡法经N_2吹扫带入反应器,通过调节水蒸气发生装置的油浴温度达到控制水蒸气流量的目的。结果发现,水蒸汽的带入对催化剂宏观的物理性质没有影响,但是催化剂表面Si-OH键的含量会随着水蒸气流量的增加而升高,从而使得金属与载体之间的相互作用变强,催化剂再分散程度大幅提升。但是另一方面生成了更多不可还原的硅酸钴,导致催化剂活性降低。3、通过对15Co/SiO_2催化剂进行还原碳化还原(RCR)处理,研究不同处理过程对催化剂中Co的相态和催化性能的影响。结果显示只进行一步还原的催化剂中Co的相态是金属Co而且主要晶面是111面。进行RC处理后催化剂中Co的相态是Co2C。然而,进行RCR处理过后Co的相态是金属Co,但是Co的晶面主要是101面和002面。这样的晶面结构差异直接导致了催化剂性能的不同,RC处理后催化剂活性很低,产物主要是甲烷;RCR处理后催化剂的活性比直接还原后的催化剂活性低,但是低碳和产物总的烯烃选择性都成倍地增长。
[Abstract]:Fischt synthesis of (FTS) is an important way to transform synthetic gas (H_2/CO) into high quality clean energy and high value-added chemical products, usually using cobalt and iron based catalysts. Compared with iron based catalyst, cobalt based Fischer catalyst has the advantages of high conversion, low water gas shift activity and low deactivation. Although FTS has been studied for a long time, there is still much room for improvement in how to improve the catalytic performance and clarify the mechanism of Fischer reaction. In general, the activity of the catalyst is closely related to the particle size of the catalyst. If the sintered catalyst particles can be redispersed and reactivated, this will be of great benefit to both theoretical research and practical industrial application. In this paper, Co/SiO_2 catalyst was prepared by impregnation method. The catalyst was treated with reductive redox (ROR) and reductive carbonization reduction (RCR). The change of catalyst structure during pretreatment was studied by means of XRD,BET,TEM and H_2-TPR, and the influence of different pretreatment process on catalyst performance was studied by using fixed-bed reactor to evaluate the catalyst. The main conclusions are as follows: 1. The catalysts with different initial particle sizes were prepared by using different cobalt precursors. The catalysts were reduced, reduced and oxidized by (RO) and reduced by redox (ROR). The results showed that these pretreatment processes had little effect on the physical structure of the catalyst, but the particle size of the catalyst changed obviously. When the catalyst was treated with RO, the particle size of the catalyst became smaller, indicating that the catalyst could be further dispersed by RO treatment. The particle size of the catalyst treated with ROR is smaller than that of the direct reduction catalyst, and the change of the particle size is related to the initial particle size of the catalyst: the larger the initial particle size, the larger the size of the catalyst. The reduction of catalyst particles after ROR treatment is greater. For example, after calcination of the catalyst prepared with cobalt chloride precursor, the particle size is 35.2 nm, and the particle size is reduced to 24.7 nm.2, after ROR treatment. The catalyst is oxidized in oxygen and water vapor. The effect of oxidation process on the structure and performance of ROR catalyst was studied. The water vapor is brought into the reactor by bubbling method through NSP 2, and the flow rate of water vapor is controlled by adjusting the oil bath temperature of the steam generator. The results show that the introduction of water vapor has no effect on the macroscopic physical properties of the catalyst, but the content of Si-OH bond on the catalyst surface will increase with the increase of water vapor flow rate, which makes the interaction between metal and support become stronger. The degree of catalyst redispersion was greatly increased. But on the other hand, more non-reductive cobalt silicate was formed, which resulted in the decrease of catalyst activity. 3. The 15Co/SiO_2 catalyst was treated by reducing carbonization and reducing (RCR). The effects of different treatment processes on the phase state and catalytic performance of Co in the catalyst were studied. The results show that the phase state of Co in the catalyst with only one step reduction is metal Co and the main crystal plane is 111face. The phase state of Co in the catalyst after RC treatment is Co2C. However, the phase state of Co after RCR treatment is metal Co, but the crystal plane of Co is mainly 101 and 002 faces. The difference of crystal surface structure leads to the difference of catalyst performance. After RC treatment, the activity of catalyst is very low, and the main product is methane. The activity of the catalyst treated with RCR was lower than that of the catalyst after direct reduction, but the selectivity of low carbon and total olefins increased exponentially.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36
本文编号：2391317
[Abstract]:Fischt synthesis of (FTS) is an important way to transform synthetic gas (H_2/CO) into high quality clean energy and high value-added chemical products, usually using cobalt and iron based catalysts. Compared with iron based catalyst, cobalt based Fischer catalyst has the advantages of high conversion, low water gas shift activity and low deactivation. Although FTS has been studied for a long time, there is still much room for improvement in how to improve the catalytic performance and clarify the mechanism of Fischer reaction. In general, the activity of the catalyst is closely related to the particle size of the catalyst. If the sintered catalyst particles can be redispersed and reactivated, this will be of great benefit to both theoretical research and practical industrial application. In this paper, Co/SiO_2 catalyst was prepared by impregnation method. The catalyst was treated with reductive redox (ROR) and reductive carbonization reduction (RCR). The change of catalyst structure during pretreatment was studied by means of XRD,BET,TEM and H_2-TPR, and the influence of different pretreatment process on catalyst performance was studied by using fixed-bed reactor to evaluate the catalyst. The main conclusions are as follows: 1. The catalysts with different initial particle sizes were prepared by using different cobalt precursors. The catalysts were reduced, reduced and oxidized by (RO) and reduced by redox (ROR). The results showed that these pretreatment processes had little effect on the physical structure of the catalyst, but the particle size of the catalyst changed obviously. When the catalyst was treated with RO, the particle size of the catalyst became smaller, indicating that the catalyst could be further dispersed by RO treatment. The particle size of the catalyst treated with ROR is smaller than that of the direct reduction catalyst, and the change of the particle size is related to the initial particle size of the catalyst: the larger the initial particle size, the larger the size of the catalyst. The reduction of catalyst particles after ROR treatment is greater. For example, after calcination of the catalyst prepared with cobalt chloride precursor, the particle size is 35.2 nm, and the particle size is reduced to 24.7 nm.2, after ROR treatment. The catalyst is oxidized in oxygen and water vapor. The effect of oxidation process on the structure and performance of ROR catalyst was studied. The water vapor is brought into the reactor by bubbling method through NSP 2, and the flow rate of water vapor is controlled by adjusting the oil bath temperature of the steam generator. The results show that the introduction of water vapor has no effect on the macroscopic physical properties of the catalyst, but the content of Si-OH bond on the catalyst surface will increase with the increase of water vapor flow rate, which makes the interaction between metal and support become stronger. The degree of catalyst redispersion was greatly increased. But on the other hand, more non-reductive cobalt silicate was formed, which resulted in the decrease of catalyst activity. 3. The 15Co/SiO_2 catalyst was treated by reducing carbonization and reducing (RCR). The effects of different treatment processes on the phase state and catalytic performance of Co in the catalyst were studied. The results show that the phase state of Co in the catalyst with only one step reduction is metal Co and the main crystal plane is 111face. The phase state of Co in the catalyst after RC treatment is Co2C. However, the phase state of Co after RCR treatment is metal Co, but the crystal plane of Co is mainly 101 and 002 faces. The difference of crystal surface structure leads to the difference of catalyst performance. After RC treatment, the activity of catalyst is very low, and the main product is methane. The activity of the catalyst treated with RCR was lower than that of the catalyst after direct reduction, but the selectivity of low carbon and total olefins increased exponentially.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36
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