Ni基乙烷脱氢催化剂的性能及其改进

doi:10.6023/A21100451

摘要/Abstract

过渡金属Ni是地球上储量丰富的金属元素, 在加氢脱硫、重整制氢等催化领域应用非常广泛, 但是关于Ni基催化剂在烷烃脱氢方面的研究较少; 因此, 本工作采用不同的方法, 制备了三种结构的Ni基负载催化剂, 即尖晶石分解型、浸渍型和钙钛矿析出型, 并在700 ℃、C₂H₆-N₂气氛中和50 mL•min^-1气体流速下, 探索了它们的乙烷脱氢性能. 结果表明: 尖晶石分解型催化剂Ni_1-_xCu_xCr₂O₄还原后在Cr₂O₃表面形成Ni-Cu合金颗粒, 能有效钝化Ni的C—C键断裂活性, 提高乙烯的选择性. Ni含量过高时, Ni不能有效地分散而形成大的金属团簇, 造成乙烷过度裂解, 乙烯选择性较低. 浸渍负载型催化剂Ni_xM_y/Al₂O₃(M为Cu或Ag) 比表面积大, 表面活性位点分散, 但活性金属与载体结合力弱, 在高温下不稳定; Cu或Ag与Ni形成合金, 可有效提高乙烯选择性, Ag较Cu的效果更佳. 钙钛矿析出型催化剂LaCr_1-_xNi_xO₃(LCNi-100x)在还原气氛中析出均匀细小的Ni颗粒, 其与基体结合力强, 抗积碳性能和稳定性较高; 含15% Ni的LCNi-15还原后(R-LCNi-15)表现出最好的催化性能, 乙烯产率最高(24%), 同时具有较好的抗积碳性能和稳定性以及氧化再生性.

关键词: Ni基催化剂, 脱氢, 乙烷转化率, 乙烯选择性, 合金化

Ethylene is one of the largest chemical products in the world, and its global demand increases significantly every year. At present, ethylene is mainly produced commercially through steam cracking of naphtha or alkane feedstocks. Catalytic dehydrogenation of ethane can effectively reduce energy loss of steam cracking. The transition metal Ni is a metal element with abundant reserves on the earth. It is widely used in the catalytic fields of hydrodesulphurization and reforming hydrogen production. However, there are few studies on Ni-based catalysts in alkanes dehydrogenation; therefore, three kinds of Ni-based supported catalysts, namely spinel decomposition-type, impregnation-type and perovskite precipitation-type, were prepared by different methods and explored for their performance in ethane dehydrogenation at 700 ℃ in C₂H₆-N₂ atmosphere at 50 mL•min^-1. The results show that the spinel decomposition-type catalyst Ni_1-_xCu_xCr₂O₄ prepared by glycine combustion method formed Ni-Cu alloy particles on the surface of Cr₂O₃ after reduction, which effectively passivated the C—C bond breaking activity of Ni and improved the selectivity of ethylene. The effect of Cu addition can be explained in geometric effect and electronic effect. When the Ni content was too high, the Ni particles could not be effectively dispersed, forming large metal clusters and resulting in excessive cracking of ethane and low ethylene selectivity. The impregnation-type catalyst Ni_xM_y/Al₂O₃ (M=Cu or Ag) had a large specific surface area and dispersed surface active sites, but the active metal particles were weakly interacted with the support and unstable at high temperatures; Cu or Ag forming an alloy with Ni effectively improved the selectivity of ethylene with Ag superior to Cu. The perovskite precipitation-type catalyst LaCr_1-_xNi_xO₃ (LCNi-100x) precipitated uniform and fine Ni particles in a reducing atmosphere, which were strongly bonded to the support and demonstrated high carbon deposition resistance and high stability; the reduced LCNi-15 (R-LCNi-15 containing 15% Ni) showed the best catalytic performance with the highest ethylene yield (24%), and high carbon deposition resistance and stability compared to commercial 13% CrO_x/Al₂O₃. Moreover, carbon-deposited R-LCNi-15 can restore catalytic activity by oxidation regeneration.

Key words: Ni-based catalysts, dehydrogenation, conversion of ethane, selectivity of ethylene, alloy

引用此文

罗俊, 贾礼超, 颜冬, 李箭. Ni基乙烷脱氢催化剂的性能及其改进[J]. 化学学报, 2022, 80(3): 317-326.

Jun Luo, Lichao Jia, Dong Yan, Jian Li. Performance and Improvement of Ni-based Catalysts for Ethane Dehydrogenation[J]. Acta Chimica Sinica, 2022, 80(3): 317-326.

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图/表 15

图1. 空白条件(无催化剂)下的乙烷脱氢(V(C2H6)/V(N2)=1/1)和乙烯聚合分解: (a)乙烷转化率和乙烯选择性随温度的变化(实线: 50 mL•min-1, 虚线: 20 mL•min-1); (b) 温度对乙烯聚合分解的影响(50 mL•min-1)

Figure 1. Ethane dehydrogenation (V(C2H6)/V(N2)=1/1) and ethylene polymerization decomposition under blank condition (without catalyst): (a) changes in ethane conversion and ethylene selectivity with temperature (solid line: 50 mL•min-1, dashed line: 20 mL•min-1); (b) the effect of temperature on ethylene polymerization decomposition (50 mL•min-1)

图2. Ni1-xCuxCr2O4催化剂还原前后的XRD图谱和微观形貌: (a)还原前和(b)还原后的XRD图谱; (c) NiCr2O4还原分解前后的微观形貌

Figure 2. XRD patterns and microstructure of Ni1-xCuxCr2O4 catalyst before and after reduction: XRD patterns of before (a) and after (b) reduction; (c) microstructure of NiCr2O4 before and after reduction

图3. Ni1-xCux/Cr2O3、Cr2O3和空白条件下的乙烷脱氢性能: (a)脱氢性能随时间的变化; (b) 90 min测试内的最高乙烯产率. 测试条件: 700 ℃, V(C2H6)/V(N2)=1/1, 50 mL•min-1. 红色乙烷转化率, 蓝色乙烯选择性

Figure 3. Performance of ethane dehydrogenation for Ni1-xCux/Cr2O3, Cr2O3 and blank condition: (a) dehydrogenation performance changes with time; (b) the highest ethylene yield under the 90 min test. Test condition: 700 ℃, V(C2H6)/V(N2)=1/1, 50 mL•min-1. Ethane conversion (red), ethylene selectivity (blue)

图4. 催化剂Ni1Cu0/Cr2O3 (a)和Ni0.1Cu0.9/Cr2O3 (b)测试后的微观形貌

Figure 4. The microstructure of tested Ni1Cu0/Cr2O3 (a) and Ni0.1Cu0.9/Cr2O3 (b)

图5. 13% CrOx/γ-Al2O3(圆圈)和Cr2O3(方块)的乙烷脱氢活性

Figure 5. Performance of ethane dehydrogenation for 13% CrOx/γ-Al2O3 (circle) and Cr2O3 (square)

图6. 负载型NixMy/γ-Al2O3的乙烷脱氢性能: (a)不同Ni负载量的催化结果(y=0); (b) Ni5和Ni7合金化(y=2), 灰方Ni, 蓝三角NiCu, 红圈NiAg, 实线乙烷转化率, 虚线乙烯选择性

Figure 6. Performance of ethane dehydrogenation for NixMy/γ-Al2O3: (a) catalytic activity of different Ni loadings (y=0); (b) alloying Ni5 and Ni7 (y=2), gray square Ni, blue triangle NiCu, red circle NiAg, ethane conversion (solid line), ethylene selectivity (dashed line)

图7. Ni5、Ni5Cu2和Ni5Ag2催化剂的Ni 2p3/2 XPS谱图

Figure 7. Ni 2p3/2 XPS spectra of Ni5, Ni5Cu2 and Ni5Ag2

图8. LaCr1-xNixO3催化剂还原前(a)和还原后(b)的XRD图谱

Figure 8. XRD patterns of LaCr1-xNixO3 catalyst before (a) and after (b) reduction

图9. LaCr0.85Ni0.15O3还原前(a)、后(b)的微观形貌和EDS元素面扫描图(c~f)

Figure 9. Microstructure of LaCr0.85Ni0.15O3 catalysts before (a) and after (b) reduction and EDS elemental mappings (c~f)

图10. 钙钛矿析出型的乙烷脱氢性能: (a) R-LCNi-05, R-LCNi-10和R-LCNi-15的催化结果; (b)不同催化剂测试180 min内的最高产率; (c) R-LCNi-15(方块)与商业13% CrOx/Al2O3(圆圈)的性能对比

Figure 10. Performance of ethane dehydrogenation for Perovskite-precipitation type: (a) catalytic activity of R-LCNi-05, R-LCNi-10 and R-LCNi-15; (b) the highest yield of different catalysts under 180 min of testing; (c) comparison of performance between R-LCNi-15 (square) and commercial 13% CrOx/Al2O3 (circle)

催化剂	乙烷转化率/%	乙烯选择性/%	碳平衡/%
R-LCNi-15	29.4	83.2	94.3
13% CrO_x/Al₂O₃	20.4	87.6	90.4

表1. R-LCNi-15和13% CrOx/Al2O3测试90 min的性能对比

Table 1. The dehydrogenation performance of R-LCNi-15 and 13% CrOx/Al2O3 tested for 90 min

图11. 催化剂测试后的表征: R-LCNi-15测试3 h后的(a) XRD图谱和(b)微观形貌; R-LCNi-15和13% CrOx/Al2O3测试后的(c)拉曼图谱、(d)热重和(e) O2-TPO测试结果

Figure 11. Characterization of tested catalysts: (a) XRD patterns and (b) microstructure of tested R-LCNi-15 catalyst; (c) Raman spectra, (d) TG curves and (e) O2-TPO profiles of R-LCNi-15 and 13% CrOx/Al2O3

图12. 积碳的R-LCNi-15经氧化再生后的催化性能

Figure 12. Catalytic performance of carbon-deposited R-LCNi-15 after oxidation regeneration

图13. 钙钛矿型掺杂Cu或Ag: (a) LCNi-05和LCNi-10掺杂Cu的催化结果; (b) LCNi-15掺杂Cu的催化结果; (c) LCNi-15掺杂Ag在900 ℃和1000 ℃煅烧后的XRD图谱; (d) LCNi-15掺杂Ag的催化结果

Figure 13. Cu or Ag doped Perovskite-type: catalytic results (a) of Cu doped LCNi-05 and LCNi-10; (b) of Cu doped LCNi-15; (c) XRD patterns of Ag doped LCNi-15 calcined at 900 ℃ or 1000 ℃; (d) catalytic result of Ag doped LCNi-15

图14. 三种不同类型Ni基催化剂的H2-TPR图谱

Figure 14. H2-TPR profiles of three kinds of Ni-based catalysts

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