新型Ni基催化剂的制备及其催化性能研究
发布时间：2018-11-13 10:21
【摘要】：目前,由于可以同时利用两种温室气体(CH_4和CO_2)生产低H_2/CO摩尔比的合成气,甲烷二氧化碳重整反应已受到越来越多的关注。而且,该反应还可以作为能量传输系统,将太阳能等转变成便于储存的化学能。虽然贵金属(Ru、Pt、Pd等)催化剂对甲烷二氧化碳重整反应具有较高的活性和抗积碳性能,但是受限于其高成本,资源丰富价格低廉的镍基催化剂成为主要的研究目标。本论文通过一步部分水解硝酸盐的方法制备了一系列介孔NiAl_2O_4/γ-Al_2O_3复合物以及不同助剂(La、Ce、Ca、Mg)改性的复合物。采用多种测试手段对其进行表征,并对其在甲烷二氧化碳重整反应中的催化性能进行了研究。具体研究内容如下:(1)成功地制备了一系列不同Ni含量的NiAl_2O_4/γ-Al_2O_3复合物。采用N_2吸脱附、XRD、TEM和XPS对材料进行表征。表征结果证明所制备的复合物具有高比表面积、大孔体积和狭窄孔径分布的蠕虫状介孔结构。在研究的Ni含量范围内,Ni~(2+)成功地的嵌入了γ-Al_2O_3的晶格中,形成了单相的NiAl_2O_4/γ-Al_2O_3固溶体。经H_2原位还原后,NiAl_2O_4/γ-Al_2O_3在甲烷重整二氧化碳反应中表现出了优异的催化活性和长时间稳定性。详细地讨论了Ni含量对NiAl_2O_4/γ-Al_2O_3在甲烷二氧化碳重整反应中的本征活性和积碳量的影响。结果显示,Ni颗粒尺寸对金属Ni活性位点的本征活性(TOF)没有明显的影响,但是小的Ni颗粒可以减小积碳速率。(2)成功地制备了具有均匀介孔结构的NiAl_2O_4/γ-Al_2O_3-La复合物,并将其应用于甲烷二氧化碳重整反应。研究结果显示还原后的催化剂在1.8×105m L/gcat h空速下对甲烷二氧化碳重整反应具有非常高的活性和稳定性。La的添加对催化剂的NiAl_2O_4/γ-Al_2O_3固溶体结构和Ni颗粒的尺寸没有产生明显的影响,但是却增强了催化剂表面的中等强度碱性和Ni~(2+)离子在催化剂表面的富集,提高了Ni活性位点的本征活性,降低了催化剂对CH_4和CO_2的活化能,阻止了积碳的形成。同时,La还能有效地阻止反应过程中γ-Al_2O_3的相转变。实验结果表明,含有3 wt%La的催化剂具有最优的催化性能。(3)制备了不同助剂(La、Ce、Ca、Mg)改性的NiAl_2O_4/γ-Al_2O_3纳米复合物。系统地研究了不同助剂对催化剂物理化学性能和催化性能的影响,并与通过传统浸渍法制备的NiAl_2O_4/La2O3/γ-Al_2O_3?imp进行了对比。表征和活性评价结果显示,助剂改性的Ni/MO_x(M=La,Ce,Ca,Mg)—γ-Al_2O_3催化剂比Ni/γ-Al_2O_3具有更高的催化活性和更好的抗积碳性能。其中,La是最有效的助剂。NiAl_2O_4前驱体经H_2还原后产生的Ni颗粒具有相似的粒径,且均匀地分散在介孔γ-Al_2O_3骨架中。而还原后的Ni/La2O3/γ-Al_2O_3?imp则表现出了相对较大的Ni颗粒。助剂的添加会增加催化剂表面中等强度碱性位点的数量,有利于CO_2的吸附和活化以及无定形碳的气化,改善催化剂的催化性能,加速积碳的消除速率,阻止载体γ-Al_2O_3的相转变。(4)随着质子交换膜燃料电池的发展,富氢气体中微量CO的甲烷化去除受到越来越多的关注。基于前面的研究结果,我们对部分水解法进行了拓展性应用,在450 ℃低温焙烧下制备了介孔Ru-Ni/γ-Al_2O_3以及Zr修饰的Ru-Ni/γ-Al_2O_3催化剂并将其应用到CO选择性甲烷化反应。详细地研究了Ru含量、Ni含量和Zr含量对催化剂的介孔结构、Ni颗粒尺寸、金属载体间的相互作用以及CO甲烷化的活性和选择性的影响。Ru-Ni/γ-Al_2O_3催化剂不但能将CO降低到10ppm以下,还具有宽达109 ℃的工作温度窗口。在一定范围内,Ru和Zr的添加都能有效的减小Ni颗粒的尺寸,改善催化剂的性能。随着Ni含量的增加,NiO物种与载体之间的相互作用逐渐减弱,还原后得到的Ni颗粒尺寸逐渐变大。优化结果显示,3Ru-25Ni/15ZrO_2—γ-Al_2O_3具有最好的催化性能。在含有15%水的标准反应条件下,3Ru-25Ni/γ-Al_2O_3和3Ru-25Ni/15ZrO_2—γ-Al_2O_3都稳定反应300 h而没有检测到CO和CH_4浓度的变化,展现了巨大的商业应用价值。
[Abstract]:At present, because two kinds of greenhouse gases (CH _ 4 and CO _ 2) can be used to produce synthesis gas with low H _ 2/ CO molar ratio, the reforming reaction of methane and carbon dioxide has attracted more and more attention. In addition, the reaction can also be used as an energy transmission system to convert solar energy and the like into chemical energy that is convenient to store. Although the noble metal (Ru, Pt, Pd, etc.) catalyst has higher activity and anti-product carbon performance to the methane carbon dioxide reforming reaction, the nickel-based catalyst which is limited by its high cost and rich in resource is the main research target. In this paper, a series of mesoporous NiAl _ 2O _ 4/ Al _ 2O _ 3 composites and a complex of different additives (La, Ce, Ca, Mg) were prepared by one-step partial hydrolysis of nitrate. The catalytic performance of the methane-carbon dioxide reforming reaction was studied by means of a variety of test methods. The results are as follows: (1) A series of NiAl _ 2O _ 4/ Al _ 2O _ 3 composites with different Ni contents were successfully prepared. The material was characterized by N _ 2 desorption, XRD, TEM and XPS. The characterization results show that the prepared composite has a worm-like mesoporous structure with a high specific surface area, a large pore volume and a narrow pore size distribution. In the range of Ni content, Ni ~ (2 +) was successfully embedded in the lattice of Al _ 2O _ 3, and a single-phase NiAl _ 2O _ 4/ Al _ 2O _ 3 solid solution was formed. After in-situ reduction of H _ 2, NiAl _ 2O _ 4/ Al _ 2O _ 3 exhibited excellent catalytic activity and long-term stability in the reaction of methane reforming carbon dioxide. The effect of Ni content on the intrinsic activity and product carbon content of NiAl _ 2O _ 4/ Al _ 2O _ 3 in methane-carbon dioxide reforming reaction was discussed in detail. The results show that the Ni particle size has no significant effect on the intrinsic activity (TOF) of the metal Ni active site, but the small Ni particles can reduce the product carbon rate. (2) NiAl _ 2O _ 4/ Al _ 2O _ 3-La complex with uniform dielectric pore structure was successfully prepared, and it was applied to the methane-carbon dioxide reforming reaction. The results show that the reduced catalyst has very high activity and stability under the space velocity of 1. 8-105m L/ gcat h. The addition of La has no obvious influence on the structure of the NiAl _ 2O _ 4/ Al-Al _ 2O _ 3 solid solution structure and the size of the Ni particles, but the enrichment of the medium-strength basic and the Ni-(2 +) ions on the surface of the catalyst is enhanced, the intrinsic activity of the Ni active site is improved, the activation energy of the catalyst on the CH _ 4 and the CO _ 2 is reduced, and the formation of the product carbon is prevented. In addition, La can effectively prevent the phase transition of Al _ 2O _ 3 during the reaction. The experimental results show that the catalyst with 3 wt% La has the optimum catalytic performance. (3) NiAl _ 2O _ 4/ Al _ 2O _ 3 nanocomposites with different additives (La, Ce, Ca, Mg) were prepared. The effects of different additives on the physical and chemical properties and catalytic properties of the catalyst were studied systematically and compared with the NiAl _ 2O _ 4/ La2O3/ Al _ 2O _ 3? imp prepared by the traditional impregnation method. The results of characterization and activity show that the auxiliary modified Ni/ MO _ x (M = La, Ce, Ca, Mg)-Al _ 2O _ 3 catalyst has higher catalytic activity and better anti-product carbon performance than Ni/ Ni-Al _ 2O _ 3. in which La is the most effective aid. The NiAl _ 2O _ 4 precursor has a similar particle size with the Ni particles produced after the reduction of H _ 2, and is uniformly dispersed in the mesoporous Al _ 2O _ 3 framework. The reduced Ni/ La2O3/ Al-Al _ 2O _ 3? imp exhibited relatively large Ni particles. The addition of the auxiliary agent increases the number of medium-strength basic sites on the surface of the catalyst, is favorable for the adsorption and activation of the CO _ 2 and the gasification of the amorphous carbon, improves the catalytic performance of the catalyst, accelerates the removal rate of the product carbon, and prevents the phase transition of the carrier F-Al _ 2O _ 3. (4) With the development of the proton exchange membrane fuel cell, the methane removal of the trace CO in the hydrogen-rich gas is more and more concerned. Based on the previous research results, we applied the partial hydrolysis method to prepare the Ru-Ni/ Al-Al _ 2O _ 3 and Zr-modified Ru-Ni/ Al _ 2O _ 3 catalyst at 450 鈩，
本文编号：2328813
[Abstract]:At present, because two kinds of greenhouse gases (CH _ 4 and CO _ 2) can be used to produce synthesis gas with low H _ 2/ CO molar ratio, the reforming reaction of methane and carbon dioxide has attracted more and more attention. In addition, the reaction can also be used as an energy transmission system to convert solar energy and the like into chemical energy that is convenient to store. Although the noble metal (Ru, Pt, Pd, etc.) catalyst has higher activity and anti-product carbon performance to the methane carbon dioxide reforming reaction, the nickel-based catalyst which is limited by its high cost and rich in resource is the main research target. In this paper, a series of mesoporous NiAl _ 2O _ 4/ Al _ 2O _ 3 composites and a complex of different additives (La, Ce, Ca, Mg) were prepared by one-step partial hydrolysis of nitrate. The catalytic performance of the methane-carbon dioxide reforming reaction was studied by means of a variety of test methods. The results are as follows: (1) A series of NiAl _ 2O _ 4/ Al _ 2O _ 3 composites with different Ni contents were successfully prepared. The material was characterized by N _ 2 desorption, XRD, TEM and XPS. The characterization results show that the prepared composite has a worm-like mesoporous structure with a high specific surface area, a large pore volume and a narrow pore size distribution. In the range of Ni content, Ni ~ (2 +) was successfully embedded in the lattice of Al _ 2O _ 3, and a single-phase NiAl _ 2O _ 4/ Al _ 2O _ 3 solid solution was formed. After in-situ reduction of H _ 2, NiAl _ 2O _ 4/ Al _ 2O _ 3 exhibited excellent catalytic activity and long-term stability in the reaction of methane reforming carbon dioxide. The effect of Ni content on the intrinsic activity and product carbon content of NiAl _ 2O _ 4/ Al _ 2O _ 3 in methane-carbon dioxide reforming reaction was discussed in detail. The results show that the Ni particle size has no significant effect on the intrinsic activity (TOF) of the metal Ni active site, but the small Ni particles can reduce the product carbon rate. (2) NiAl _ 2O _ 4/ Al _ 2O _ 3-La complex with uniform dielectric pore structure was successfully prepared, and it was applied to the methane-carbon dioxide reforming reaction. The results show that the reduced catalyst has very high activity and stability under the space velocity of 1. 8-105m L/ gcat h. The addition of La has no obvious influence on the structure of the NiAl _ 2O _ 4/ Al-Al _ 2O _ 3 solid solution structure and the size of the Ni particles, but the enrichment of the medium-strength basic and the Ni-(2 +) ions on the surface of the catalyst is enhanced, the intrinsic activity of the Ni active site is improved, the activation energy of the catalyst on the CH _ 4 and the CO _ 2 is reduced, and the formation of the product carbon is prevented. In addition, La can effectively prevent the phase transition of Al _ 2O _ 3 during the reaction. The experimental results show that the catalyst with 3 wt% La has the optimum catalytic performance. (3) NiAl _ 2O _ 4/ Al _ 2O _ 3 nanocomposites with different additives (La, Ce, Ca, Mg) were prepared. The effects of different additives on the physical and chemical properties and catalytic properties of the catalyst were studied systematically and compared with the NiAl _ 2O _ 4/ La2O3/ Al _ 2O _ 3? imp prepared by the traditional impregnation method. The results of characterization and activity show that the auxiliary modified Ni/ MO _ x (M = La, Ce, Ca, Mg)-Al _ 2O _ 3 catalyst has higher catalytic activity and better anti-product carbon performance than Ni/ Ni-Al _ 2O _ 3. in which La is the most effective aid. The NiAl _ 2O _ 4 precursor has a similar particle size with the Ni particles produced after the reduction of H _ 2, and is uniformly dispersed in the mesoporous Al _ 2O _ 3 framework. The reduced Ni/ La2O3/ Al-Al _ 2O _ 3? imp exhibited relatively large Ni particles. The addition of the auxiliary agent increases the number of medium-strength basic sites on the surface of the catalyst, is favorable for the adsorption and activation of the CO _ 2 and the gasification of the amorphous carbon, improves the catalytic performance of the catalyst, accelerates the removal rate of the product carbon, and prevents the phase transition of the carrier F-Al _ 2O _ 3. (4) With the development of the proton exchange membrane fuel cell, the methane removal of the trace CO in the hydrogen-rich gas is more and more concerned. Based on the previous research results, we applied the partial hydrolysis method to prepare the Ru-Ni/ Al-Al _ 2O _ 3 and Zr-modified Ru-Ni/ Al _ 2O _ 3 catalyst at 450 鈩，
本文编号：2328813
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