SrO助催化剂对Fe1-  x O基熔铁氨合成催化剂性能的影响

doi:10.16085/j.issn.1000-6613.2018-0382

摘要/Abstract

摘要：

采用高温熔融法制备了不同SrO含量的Fe_1- _x O基氨合成催化剂。在类似工业条件下（15MPa、30000h^-1）使用固定床反应器对催化剂进行了氨合成（氮的催化加氢）活性评价，并采用X射线能谱仪（EDS）、程序升温还原（H₂-TPR）、N₂程序升温脱附（N₂-TPD）、X射线粉末衍射（XRD）对样品进行表征。结果表明，随着SrO含量的增加，催化剂的活性先增加后降低，呈现出火山型活性变化趋势。当SrO质量分数为0.4%时，催化剂活性最高。SrO存在表面偏析现象，且SrO的添加并没有促进或明显抑制催化剂的还原。少量SrO的添加降低了N₂的解离活化能或降低了NH _x 物种的稳定性，提高了催化剂的活性；SrO含量进一步增加，覆盖了表面部分活性位，消耗了体相的重要结构助催化剂Al，降低了催化剂的活性和耐热性能。

关键词: 氨合成, 催化剂, 固定床, 加氢, SrO助催化剂, 偏析, 火山型活性曲线

Abstract:

Wüstite based catalysts for ammonia synthesis promoted with different amounts of SrO were prepared by fusing method．Under industrial condition (15MPa、30000h^-1)， the activity tests on a fixed-bed show that the catalytic performance of the catalysts (catalytic hydrogenation for nitrogen) increases at first and then decreases with SrO content， presenting a typical volcano curve．The optimal catalyst was obtained when 0.4% SrO promoter was added． The characterizations including EDS， H₂-TPR， N₂-TPD and XRD indicate that strontium segregates on the surface of catalysts．However， no obvious influence on the reduction of the catalysts was observed． Small amounts of SrO improve the catalytic performance due to the decrease in the N₂ dissociation activation energy or destabilization of NH _x ．However， the addition of excessive SrO covers part of active sites，and they can react with Al which is an important structural promoter for ammonia synthesis catalysts． As a result， the activity and thermal-stability was decreased．

Key words: ammonia synthesis, catalyst, fixed-bed, hydrogenation, SrO promoter, segregation, volcano curve

中图分类号:

O643

李林辉,刘化章,韩文锋,黎志,李蕾,王志昆. SrO助催化剂对Fe_1- _x O基熔铁氨合成催化剂性能的影响[J]. 化工进展, 2019, 38(03): 1371-1376.

Linhui LI,Huazhang LIU,Wenfeng HAN,Zhi LI,Lei LI,Zhikun WANG. Effect of SrO promoter on the activity and thermal-stability of wüstite based catalyst for ammonia synthesis[J]. Chemical Industry and Engineering Progress, 2019, 38(03): 1371-1376.

图/表 8

参考文献 19

1	刘化章 . 合成氨工业: 过去、现在和未来[J]. 化工进展，2013，32(9): 1995-2005．
	LIU H Z . Ammonia synthesis: industry past, present and future[J]. Chemical Industry and Engineering Progress， 2013， 32(9): 1995-2005．
2	刘化章 . 氨合成催化剂[M]. 北京: 化学工业出版社, 2007: 30．
	LIU H Z . Ammonia synthesis catalysts[M]. Beijing: Chemical Industry Press, 2007: 30．
3	LIU H Z , LI X N . The precursor phase composition of iron catalyst and discovery of FeO based catalyst for ammonia synthesis[J]. Science China Chemistry, 1995, 38(5): 529-537．
4	MULLAS A R , CHOUDHARY V R . Oxidative conversion of ethane to ethylene over supported SrO-promoted Er₂O₃ catalyst[J]. Journal of Molecular Catalysis A: Chemical，2004，223(1): 259-262．
5	JIAO Y ， ZHANG J ， DU Y ，et al . Hydrogen production by catalytic steam reforming of hydrocarbon fuels over Ni/Ce-Al₂O₃ bifunctional catalysts: effects of SrO addition[J]. International Journal of Hydrogen Energy，2016，41(31): 13436-13447．
6	徐秀峰, 索掌怀, 齐世学, 等 . SrO对Al₂O₃载体的改性及MnO_x/SrO-Al₂O₃催化剂的甲烷燃烧活性[J]. 分子催化, 2002, 16(2): 131-134．
	XU X F ， SUO Z H ， QI S X ，et al ．Modification of Al₂O₃ by SrO and the catalytic activity of MnO _x /SrO-Al₂O₃ for CH₄ combustion[J]．Journal of Molecular Catalysis，2002，16(2): 131-134．
7	余林, 徐奕德, 黄家生, 等 . 甲烷在SrO-La₂O₃/CaO催化剂上的氧化偶联Ⅰ. SrO对La₂O₃/CaO催化剂的助催化作用[J]. 催化学报, 1993, 14(1): 33-38．
	YU L ， XU Y D ， HUANG J S ，et al . Oxidative coupling of methane over SrO-La₂O₃/CaO catalysts Ⅰ. Promotive effect of SrO additive on La₂O₃/CaO catalysts[J]. Chinese Journal of Catalysis，1993，14(1)：33-38．
8	杨艳玲, 董玲玉, 夏文生, 等 . Ca，Sr共掺杂铈氧化物及其在甲烷氧化偶联反应中的应用[J]. 高等学校化学学报, 2016, 37(12): 2206-2214．
	YANG Y L ， DONG L Y ， XIA W S ，et al ．Ca，Sr co-doped ceria and its application in oxidative coupling of methane[J]．Chemical Journal of Chinese Universities，2016，37(12)：2206-2214．
9	HAN W F , HUANG S L , CHENG T H , et al . Promotion of Nb₂O₅ on the wustite-based iron catalyst for ammonia synthesis[J].Applied Surface Science，2015，353：17-23．
10	刘化章, 胡樟能, 李小年, 等 . FeO基氨合成催化剂[J]．化工学报，1994, 45(4): 385-392．
	LIU H Z , HU Z N , LI X N , et al . FeO based catalyst for ammonia synthesis[J]. Journal of Chemical Industry & Engineering, 1994, 45(4)：385-392．
11	STAMENKOVIĆ V , SCHMIDT T J , ROSS P N , et al . Surface segregation effects in electrocatalysis：kinetics of oxygen reduction reaction on polycrystalline Pt₃Ni alloy surfaces[J]. Journal of Electroanalytical Chemistry, 2002, 554/555(3)：191-199．
12	GAO F , WANG Y , GOODMAN D W . CO oxidation over AuPd(100) from ultrahigh vacuum to near-atmospheric pressures：CO adsorption-induced surface segregation and reaction kinetics[J]. Journal of Physical Chemistry C, 2009, 113(33): 14993-15000．
13	ARABCZYK W , NARKIEWICZ A U , MOSZYNSKI D . Double-layer model of the fused iron catalyst for ammonia synthesis[J]. Langmuir, 1999, 15(18)：5785-5789．
14	PERNICONE N , FERRERO F , ROSSETTI I , et al . Wustite as a new precursor of industrial ammonia synthesis catalysts[J]. Applied Catalysis A: General, 2004, 251(1): 121-129．
15	DAHL S , LOGADOTTIR A , JACOBSEN C J H , et al ．Electronic factors in catalysis: the volcano curve and the effect of promotion in catalytic ammonia synthesis[J]. Applied Catalysis A: General, 2001, 222(1/2)：19-29．
16	LOGADOTTIR A , ROD T H, NØRSKOV J K , et al ．The Brønsted-Evans-Polanyi relation and the volcano plot for ammonia synthesis over transition metal catalysts[J]. Journal of Catalysis, 2001, 197(2)：229-231．
17	李小年, 陈诵英 . 助催化剂对Fe_1- _x O基氨合成催化剂还原性能的影响[J]. 催化学报, 1998, 19(3): 24-28．
	LI X N , CHEN S Y ．The effect of promoters on reduction performance of Fe_1- _x O based ammonia synthesis catalyst[J]. Chinese Journal of Catalysis, 1998, 19(3): 24-28．
18	李小年, 刘化章, 许裕生, 等 . 助剂对氨合成Fe_1- _x O基催化剂母体歧化反应的抑制作用的穆斯堡尔谱研究[J]. 催化学报, 1999, 20(1)：76-80．
	LI X N , LIU H Z , XU Y S , et al . Mossbauer study on the inhibition of promoters on the disproportionation of Fe_1- _x O catalyst for ammonia synthesis[J]. Chinese Journal of Catalysis, 1999, 20(1)：76-80．
19	李小年, 刘化章, 许裕生, 等 . Fe_1- _x O基氨合成催化剂的穆斯堡尔谱研究[C]//全国催化学术会议, 1998．
	LI X N , LIU H Z , XU Y S , et al . Mossbauer study of Fe_1- _x O catalysts for ammonia synthesis[C]// National Catalytic Academic Conference, 1998．

SrO质量分数/%	耐热系数α _450℃	耐热系数α _425℃	耐热系数α _400℃
0	0.97	–0.30	–0.45
0.2	0.96	0.97	0.51
0.3	1.08	–0.57	0.18
0.4	0.91	–0.24	–1.63
0.5	–0.69	–2.27	–1.23
0.8	–3.16	–4.24	–5.21

SrO质量分数/%	耐热系数α _450℃	耐热系数α _425℃	耐热系数α _400℃
0	0.97	–0.30	–0.45
0.2	0.96	0.97	0.51
0.3	1.08	–0.57	0.18
0.4	0.91	–0.24	–1.63
0.5	–0.69	–2.27	–1.23
0.8	–3.16	–4.24	–5.21

SrO质量分数/%	元素质量分数/%
SrO质量分数/%	Fe	O	Sr
0	78.73	16.01	0
0.2	77.66	16.91	0.40
0.3	77.47	17.63	0.51
0.4	77.55	12.81	0.72
0.5	71.52	19.66	0.99
0.8	70.93	21.10	1.46

SrO质量分数/%	元素质量分数/%
SrO质量分数/%	Fe	O	Sr
0	78.73	16.01	0
0.2	77.66	16.91	0.40
0.3	77.47	17.63	0.51
0.4	77.55	12.81	0.72
0.5	71.52	19.66	0.99
0.8	70.93	21.10	1.46

SrO 质量分数/%	含Al物相		Ca₂Fe₂O₄ 质量分数/%	FeO 质量分数/%
SrO 质量分数/%	物相	质量分数/%	Ca₂Fe₂O₄ 质量分数/%	FeO 质量分数/%
0	3CaO·Al₂O₃	4.07	8.04	87.89
0.2	3CaO·Al₂O₃	4.17	8.56	87.27
0.4	3CaO·Al₂O₃	6.67	9.23	84.10
0.8	SrO·2Al₂O₃	6.37	8.25	85.37
2	12SrO·7Al₂O₃	11.53	11.23	77.24
4	3SrO·Al₂O₃	12.11	10.60	77.28