預處理過程對鈷基費托催化劑結(jié)構(gòu)及性能的影響
發(fā)布時間：2018-12-25 15:44
【摘要】：費托合成(FTS)是將合成氣(H_2/CO)轉(zhuǎn)化為優(yōu)質(zhì)清潔能源和高附加值化工產(chǎn)品的重要途徑,通常采用鈷基催化劑和鐵基催化劑。相比于鐵基催化劑,鈷基費托催化劑具有高轉(zhuǎn)化率、不易失活和低水煤氣變換活性的優(yōu)點。雖然FTS已經(jīng)研究了很長時間,但是在如何提高催化劑性能和弄清楚費托反應的機理方面還是有很大的提升空間。一般而言,催化劑的活性與催化的粒子大小存在重要的聯(lián)系,如果能夠使燒結(jié)的催化劑顆粒進行再分散從而重新獲得活性,這將對理論研究和實際工業(yè)應用都大有裨益。本文通過浸漬法制備了Co/SiO_2催化劑,對催化劑進行還原氧化還原(ROR)和還原碳化還原(RCR)處理。通過XRD、BET、TEM和H_2-TPR等表征手段研究預處理過程中催化劑結(jié)構(gòu)的變化;采用固定床反應器進行催化劑評價,研究不同預處理過程對催化劑性能的影響。主要得到以下結(jié)論:1、通過使用不同鈷的前驅(qū)體制備了具有不同初始粒子大小的催化劑,對催化劑進行還原、還原氧化(RO)和還原氧化還原(ROR)處理。結(jié)果發(fā)現(xiàn),這些預處理過程對催化劑的物理結(jié)構(gòu)沒有太大的影響;但是催化劑的顆粒尺寸發(fā)生了很明顯的變化。當進行RO處理時,催化劑的顆粒明顯變小,說明RO處理可以使催化劑進一步分散。進行ROR處理得到的催化劑顆粒要比直接還原的催化劑顆粒小,而且這種顆粒尺寸的變化程度與催化劑初始顆粒大小有關:催化劑初始顆粒越大,ROR處理后催化劑顆粒減少的程度越大。例如使用氯化鈷前驅(qū)體制備的催化劑焙燒后顆粒大小為35.2 nm,經(jīng)過ROR處理后顆粒減小到24.7 nm。2、通過對催化劑在氧氣和水蒸氣中進行氧化處理,研究ROR過程中的氧化過程對催化劑結(jié)構(gòu)和性能的影響。水蒸氣通過鼓泡法經(jīng)N_2吹掃帶入反應器,通過調(diào)節(jié)水蒸氣發(fā)生裝置的油浴溫度達到控制水蒸氣流量的目的。結(jié)果發(fā)現(xiàn),水蒸汽的帶入對催化劑宏觀的物理性質(zhì)沒有影響,但是催化劑表面Si-OH鍵的含量會隨著水蒸氣流量的增加而升高,從而使得金屬與載體之間的相互作用變強,催化劑再分散程度大幅提升。但是另一方面生成了更多不可還原的硅酸鈷,導致催化劑活性降低。3、通過對15Co/SiO_2催化劑進行還原碳化還原(RCR)處理,研究不同處理過程對催化劑中Co的相態(tài)和催化性能的影響。結(jié)果顯示只進行一步還原的催化劑中Co的相態(tài)是金屬Co而且主要晶面是111面。進行RC處理后催化劑中Co的相態(tài)是Co2C。然而,進行RCR處理過后Co的相態(tài)是金屬Co,但是Co的晶面主要是101面和002面。這樣的晶面結(jié)構(gòu)差異直接導致了催化劑性能的不同,RC處理后催化劑活性很低,產(chǎn)物主要是甲烷;RCR處理后催化劑的活性比直接還原后的催化劑活性低,但是低碳和產(chǎn)物總的烯烴選擇性都成倍地增長。
[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.
【學位授予單位】：江南大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O643.36
本文編號：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.
【學位授予單位】：江南大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O643.36
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