堿金屬活性組分催化碳煙燃燒性能及機理
發(fā)布時間：2018-08-08 18:58
【摘要】：柴油車尾氣中排放的碳煙顆粒物對環(huán)境和人類健康帶來嚴重的危害。因此,如何有效控制顆粒物的排放受到研究者的廣泛的關(guān)注。目前,解決這一問題最有效的技術(shù)是DPF(diesel particulate filters)技術(shù)。該技術(shù)的關(guān)鍵是開發(fā)一種高效的催化劑以降低碳煙的起燃溫度。研究表明,堿金屬催化劑具有優(yōu)異的催化碳煙燃燒活性。然而對于其催化作用機理一直存在爭議。大部分人認為堿金屬能夠增加催化劑與碳煙的接觸效率,從而有效地促進碳煙氧化。而我們課題組在前期工作的基礎(chǔ)上認為,堿金屬物種除了作為助劑改善接觸之外,其本身也具有催化活性。為了證明這一猜想,我們對催化劑進行了設(shè)計:將堿金屬限域在具有孔道材料的催化劑中,使其不與碳煙接觸。由于ZSM-5分子篩具有有序的三維微孔結(jié)構(gòu)和陽離子交換能力。因此我們選取ZSM-5為載體,將堿金屬(Na、K、Cs)用離子交換法引入ZSM-5微孔中,制備了M-ZSM-5-25(M=Na/K/Cs)催化劑,通過XRD、BET、SEM、ICP、FT-IR、Raman、XAFS、NH_3-TPD等手段對其物理化學(xué)性質(zhì)進行表征,證明堿金屬的存在位置位于離子交換位。并通過O_2-TPO和等溫反應(yīng)對其催化碳煙氧化表觀活性和內(nèi)在活性進行了探究。發(fā)現(xiàn)該類催化劑展現(xiàn)出了碳煙氧化活性,并且其活性與堿金屬本身的性質(zhì)有關(guān)。此外,對其催化碳煙氧化機理進行了研究,對不同K含量的ZSM-5的活性進行比較,發(fā)現(xiàn)隨著K含量的增加,催化劑催化碳煙燃燒活性增強。并通過同位素示蹤實驗證實了K-ZSM-5能夠使氣相氧活化。氣相氧的活化來源于活性組分K。將堿金屬引入分子篩中,已經(jīng)證明堿金屬物種可以作為活性組分用于催化碳煙氧化。為了證明這一結(jié)論在其他體系中的適用性,我們設(shè)計了另外一種催化劑,將K引入到具有隧道結(jié)構(gòu)的Ti O_2載體中,作進一步的研究。首先利用固相法制備了棒狀的KTi_8O_(16)催化劑,發(fā)現(xiàn)K的加入,有助于改善Ti O_2催化碳煙燃燒活性。此外,為了進一步提高該類催化劑的活性,利用不同的方法對K含量進行了調(diào)控,制備了一系列形貌為顆粒狀的K_xTi_8O_(16)催化劑。利用XRD、FT-IR、XAFS等技術(shù)確定了制備樣品中K物種的存在狀態(tài)。結(jié)合XPS和O_2-TPO表觀活性測試,排除了氧空位對催化活性的影響。并且對催化劑內(nèi)在活性進行測試,發(fā)現(xiàn)其與表觀活性結(jié)果一致。該體系進一步證明了堿金屬物種能夠作為活性組分起到催化碳煙燃燒的作用。
[Abstract]:The soot particles emitted from diesel exhaust are harmful to the environment and human health. Therefore, how to effectively control the emission of particulate matter has been widely concerned by researchers. At present, the most effective technology to solve this problem is DPF (diesel particulate filters) technology. The key of this technology is to develop an efficient catalyst to reduce the ignition temperature of soot. The results show that alkali metal catalysts have excellent catalytic activity for soot combustion. However, the mechanism of its catalytic action has been controversial. Most people think that alkali metal can increase the contact efficiency between the catalyst and soot, thus effectively promoting soot oxidation. On the basis of the previous work, our group thinks that alkali metal species have catalytic activity in addition to improving contact as auxiliaries. In order to prove this conjecture, the catalyst is designed: the alkali metal is confined to the catalyst with pore material so that it is not in contact with soot. Because ZSM-5 molecular sieve has ordered three dimensional micropore structure and cation exchange ability. Therefore, M-ZSM-5-25 (M=Na/K/Cs) catalyst was prepared by using ZSM-5 as the carrier and introduced into the ZSM-5 micropore by ion exchange method. The physicochemical properties of M-ZSM-5-25 (M=Na/K/Cs) catalyst were characterized by means of XRDX BETSMEM, FT-IR, Ramanhe, XAFSS-NH3-TPD, etc. It is proved that the location of alkali metal is in the ion exchange site. The apparent and intrinsic activity of soot oxidation was investigated by O_2-TPO and isothermal reaction. It is found that this kind of catalyst exhibits soot oxidation activity, and its activity is related to the properties of alkali metal itself. In addition, the mechanism of catalytic soot oxidation was studied, and the activity of ZSM-5 with different K content was compared. It was found that the catalytic soot combustion activity increased with the increase of K content. The isotopic tracer experiments show that K-ZSM-5 can activate oxygen in gas phase. The activation of gaseous oxygen originates from the active component K. It has been proved that alkali metal species can be used as active component to catalyze soot oxidation by introducing alkali metal into molecular sieve. To prove the applicability of this conclusion in other systems, we have designed another catalyst to introduce K into TiO2 carrier with tunnel structure for further study. Firstly, the rod-like KTi _ 8O _ (16) catalyst was prepared by solid phase method. It was found that the addition of K was helpful to improve the catalytic activity of TIO _ 2 for soot combustion. In addition, in order to further improve the activity of these catalysts, K content was regulated by different methods, and a series of K _ XTi _ 8O _ (16) catalysts with granular morphology were prepared. The state of K species in the prepared samples was determined by using XRDX FT-IR and XAFS techniques. The effect of oxygen vacancy on catalytic activity was excluded by XPS and O_2-TPO. The intrinsic activity of the catalyst was tested and it was found that it was consistent with the apparent activity. It is further proved that alkali metal species can act as active components to catalyze soot combustion.
【學(xué)位授予單位】：濟南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：X734.2;O643.36
本文編號：2172711
[Abstract]:The soot particles emitted from diesel exhaust are harmful to the environment and human health. Therefore, how to effectively control the emission of particulate matter has been widely concerned by researchers. At present, the most effective technology to solve this problem is DPF (diesel particulate filters) technology. The key of this technology is to develop an efficient catalyst to reduce the ignition temperature of soot. The results show that alkali metal catalysts have excellent catalytic activity for soot combustion. However, the mechanism of its catalytic action has been controversial. Most people think that alkali metal can increase the contact efficiency between the catalyst and soot, thus effectively promoting soot oxidation. On the basis of the previous work, our group thinks that alkali metal species have catalytic activity in addition to improving contact as auxiliaries. In order to prove this conjecture, the catalyst is designed: the alkali metal is confined to the catalyst with pore material so that it is not in contact with soot. Because ZSM-5 molecular sieve has ordered three dimensional micropore structure and cation exchange ability. Therefore, M-ZSM-5-25 (M=Na/K/Cs) catalyst was prepared by using ZSM-5 as the carrier and introduced into the ZSM-5 micropore by ion exchange method. The physicochemical properties of M-ZSM-5-25 (M=Na/K/Cs) catalyst were characterized by means of XRDX BETSMEM, FT-IR, Ramanhe, XAFSS-NH3-TPD, etc. It is proved that the location of alkali metal is in the ion exchange site. The apparent and intrinsic activity of soot oxidation was investigated by O_2-TPO and isothermal reaction. It is found that this kind of catalyst exhibits soot oxidation activity, and its activity is related to the properties of alkali metal itself. In addition, the mechanism of catalytic soot oxidation was studied, and the activity of ZSM-5 with different K content was compared. It was found that the catalytic soot combustion activity increased with the increase of K content. The isotopic tracer experiments show that K-ZSM-5 can activate oxygen in gas phase. The activation of gaseous oxygen originates from the active component K. It has been proved that alkali metal species can be used as active component to catalyze soot oxidation by introducing alkali metal into molecular sieve. To prove the applicability of this conclusion in other systems, we have designed another catalyst to introduce K into TiO2 carrier with tunnel structure for further study. Firstly, the rod-like KTi _ 8O _ (16) catalyst was prepared by solid phase method. It was found that the addition of K was helpful to improve the catalytic activity of TIO _ 2 for soot combustion. In addition, in order to further improve the activity of these catalysts, K content was regulated by different methods, and a series of K _ XTi _ 8O _ (16) catalysts with granular morphology were prepared. The state of K species in the prepared samples was determined by using XRDX FT-IR and XAFS techniques. The effect of oxygen vacancy on catalytic activity was excluded by XPS and O_2-TPO. The intrinsic activity of the catalyst was tested and it was found that it was consistent with the apparent activity. It is further proved that alkali metal species can act as active components to catalyze soot combustion.
【學(xué)位授予單位】：濟南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：X734.2;O643.36
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