新型Ni基催化劑的制備及其催化性能研究
發(fā)布時間：2018-11-13 10:21
【摘要】：目前,由于可以同時利用兩種溫室氣體(CH_4和CO_2)生產低H_2/CO摩爾比的合成氣,甲烷二氧化碳重整反應已受到越來越多的關注。而且,該反應還可以作為能量傳輸系統(tǒng),將太陽能等轉變成便于儲存的化學能。雖然貴金屬(Ru、Pt、Pd等)催化劑對甲烷二氧化碳重整反應具有較高的活性和抗積碳性能,但是受限于其高成本,資源豐富價格低廉的鎳基催化劑成為主要的研究目標。本論文通過一步部分水解硝酸鹽的方法制備了一系列介孔NiAl_2O_4/γ-Al_2O_3復合物以及不同助劑(La、Ce、Ca、Mg)改性的復合物。采用多種測試手段對其進行表征,并對其在甲烷二氧化碳重整反應中的催化性能進行了研究。具體研究內容如下:(1)成功地制備了一系列不同Ni含量的NiAl_2O_4/γ-Al_2O_3復合物。采用N_2吸脫附、XRD、TEM和XPS對材料進行表征。表征結果證明所制備的復合物具有高比表面積、大孔體積和狹窄孔徑分布的蠕蟲狀介孔結構。在研究的Ni含量范圍內,Ni~(2+)成功地的嵌入了γ-Al_2O_3的晶格中,形成了單相的NiAl_2O_4/γ-Al_2O_3固溶體。經H_2原位還原后,NiAl_2O_4/γ-Al_2O_3在甲烷重整二氧化碳反應中表現(xiàn)出了優(yōu)異的催化活性和長時間穩(wěn)定性。詳細地討論了Ni含量對NiAl_2O_4/γ-Al_2O_3在甲烷二氧化碳重整反應中的本征活性和積碳量的影響。結果顯示,Ni顆粒尺寸對金屬Ni活性位點的本征活性(TOF)沒有明顯的影響,但是小的Ni顆�？梢詼p小積碳速率。(2)成功地制備了具有均勻介孔結構的NiAl_2O_4/γ-Al_2O_3-La復合物,并將其應用于甲烷二氧化碳重整反應。研究結果顯示還原后的催化劑在1.8×105m L/gcat h空速下對甲烷二氧化碳重整反應具有非常高的活性和穩(wěn)定性。La的添加對催化劑的NiAl_2O_4/γ-Al_2O_3固溶體結構和Ni顆粒的尺寸沒有產生明顯的影響,但是卻增強了催化劑表面的中等強度堿性和Ni~(2+)離子在催化劑表面的富集,提高了Ni活性位點的本征活性,降低了催化劑對CH_4和CO_2的活化能,阻止了積碳的形成。同時,La還能有效地阻止反應過程中γ-Al_2O_3的相轉變。實驗結果表明,含有3 wt%La的催化劑具有最優(yōu)的催化性能。(3)制備了不同助劑(La、Ce、Ca、Mg)改性的NiAl_2O_4/γ-Al_2O_3納米復合物。系統(tǒng)地研究了不同助劑對催化劑物理化學性能和催化性能的影響,并與通過傳統(tǒng)浸漬法制備的NiAl_2O_4/La2O3/γ-Al_2O_3?imp進行了對比。表征和活性評價結果顯示,助劑改性的Ni/MO_x(M=La,Ce,Ca,Mg)—γ-Al_2O_3催化劑比Ni/γ-Al_2O_3具有更高的催化活性和更好的抗積碳性能。其中,La是最有效的助劑。NiAl_2O_4前驅體經H_2還原后產生的Ni顆粒具有相似的粒徑,且均勻地分散在介孔γ-Al_2O_3骨架中。而還原后的Ni/La2O3/γ-Al_2O_3?imp則表現(xiàn)出了相對較大的Ni顆粒。助劑的添加會增加催化劑表面中等強度堿性位點的數(shù)量,有利于CO_2的吸附和活化以及無定形碳的氣化,改善催化劑的催化性能,加速積碳的消除速率,阻止載體γ-Al_2O_3的相轉變。(4)隨著質子交換膜燃料電池的發(fā)展,富氫氣體中微量CO的甲烷化去除受到越來越多的關注�；谇懊娴难芯拷Y果,我們對部分水解法進行了拓展性應用,在450 ℃低溫焙燒下制備了介孔Ru-Ni/γ-Al_2O_3以及Zr修飾的Ru-Ni/γ-Al_2O_3催化劑并將其應用到CO選擇性甲烷化反應。詳細地研究了Ru含量、Ni含量和Zr含量對催化劑的介孔結構、Ni顆粒尺寸、金屬載體間的相互作用以及CO甲烷化的活性和選擇性的影響。Ru-Ni/γ-Al_2O_3催化劑不但能將CO降低到10ppm以下,還具有寬達109 ℃的工作溫度窗口。在一定范圍內,Ru和Zr的添加都能有效的減小Ni顆粒的尺寸,改善催化劑的性能。隨著Ni含量的增加,NiO物種與載體之間的相互作用逐漸減弱,還原后得到的Ni顆粒尺寸逐漸變大。優(yōu)化結果顯示,3Ru-25Ni/15ZrO_2—γ-Al_2O_3具有最好的催化性能。在含有15%水的標準反應條件下,3Ru-25Ni/γ-Al_2O_3和3Ru-25Ni/15ZrO_2—γ-Al_2O_3都穩(wěn)定反應300 h而沒有檢測到CO和CH_4濃度的變化,展現(xiàn)了巨大的商業(yè)應用價值。
[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，
本文編號：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，
本文編號：2328813
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