EDTA-assisted preparation of highly active catalysts for Fischer-Tropsch synthesis

doi:10.16085/j.issn.1000-6613.2021-0522

Abstract

Abstract:

Fischer-Tropsch synthesis (FTS) is crucial for the conversion of natural gas, coal and biomass to clean fuels and value-added chemicals. Traditionally, the iron catalysts for FTS are mainly supported on alumina and silica. However, the interaction between metal and support hindered the formation of active phase iron carbide, resulting in low activity of the catalyst. In this study, Fe/Al₂O₃ catalyst was prepared by EDTA complex impregnation and the dispersion of iron species on alumina support was improved by coulomb interaction between positively charged hydroxyl (OH₂⁺) and [Fe(EDTA)]^- complex anion. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area (BET), in situ infrared (in-situ IR) and other means were used. The results showed that the addition of EDTA could enhance the sintering resistance of Fe. In the calcining process, EDTA can be decomposed into small organic molecules, which can reduce the iron species in the catalyst to Fe²⁺ and thus is conducive to the reduction of the catalyst. Besides, more active centers enhanced the CO adsorption capacity of the catalyst. In-situ IR experiments showed that the catalyst prepared with EDTA enriched the active species easier, which improved the conversion of CO. The product distribution in hydrocarbons was improved by adjusting the content of alkali metal sodium in the system. The Fe-Na/Al₂O₃ catalyst prepared by EDTA complexation showed high CO conversion (88.5%) and high selectivity of C₂~C $_{4}^{=}$ and C₅~C₁₁ (total of 71.2%) at a low hydrogen carbon ratio (H₂/CO=1/1).

Key words: fixed-bed, syngas, Fischer-Tropsch synthesis, catalyst, hydrocarbons, EDTA

摘要：

费托合成（FTS）对天然气、煤炭和生物质向清洁运输燃料和增值化学品的转化至关重要。传统上，用于FTS的负载型铁催化剂主要是以氧化铝和二氧化硅为载体。然而，金属与载体的相互作用阻碍了活性相碳化铁的形成，使得催化剂活性较低。本文通过乙二胺四乙酸（EDTA）络合浸渍制备了Fe/Al₂O₃催化剂，通过带正电荷的羟基（OH $_{2}^{+}$ ）与[Fe(EDTA)]^-配合物阴离子之间的库仑相互作用来提高氧化铝载体上铁物种的分散度。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X射线光电子能谱（XPS）、比表面积（BET）、原位红外（In-situ IR）等手段进行表征分析。结果表明，添加EDTA有助于增强Fe的抗烧结性。在煅烧络合浸渍制备样品的过程中，EDTA可以分解为具有还原性质的有机小分子，将催化剂中的铁物种还原为Fe²⁺，有利于催化剂的还原；更多活性中心增强了催化剂对CO的吸附量。原位红外实验表明，EDTA辅助制备的催化剂更容易富集活性物种，从而提高CO的转化率。调节体系中碱金属钠的含量改善了烃内产物分布。在较低的氢碳比（H₂/CO=1/1）下，EDTA络合制备的Fe-Na/Al₂O₃催化剂显示出高的CO转化率（88.5%）以及最大的C₂~C₄=和C₅~C₁₁选择性，总选择性达71.2%。

关键词: 固定床, 合成气, 费托合成, 催化剂, 碳氢化合物, 乙二胺四乙酸

CLC Number:

O643.3

ZHAO Xiao, CHEN Zhongshun, TANG Zhongqiang, SHI Xuan, DAI Chengyi, MA Xiaoxun. EDTA-assisted preparation of highly active catalysts for Fischer-Tropsch synthesis[J]. Chemical Industry and Engineering Progress, 2022, 41(2): 759-769.

赵潇, 陈中顺, 唐忠强, 石轩, 代成义, 马晓迅. EDTA辅助制备高活性费托合成催化剂[J]. 化工进展, 2022, 41(2): 759-769.

Figures/Tables 22

样本代码	Fe/mol	EDTA/mol	EDTA-2Na/mol	NaNO₃/mol
10Fe/Al₂O₃	M	0	0	0
10Fe2.5E/Al₂O₃	M	0.25M	0	0
10Fe5E/Al₂O₃	M	0.5M	0	0
10Fe7.5E/Al₂O₃	M	0.75M	0	0
10Fe10E/Al₂O₃	M	M	0	0
10Fe10Na/Al₂O₃	M	0	0	M
10Fe10E5Na/Al₂O₃	M	0.75M	0.25M	0
10Fe5E10Na/Al₂O₃	M	0	0.5M	0
10Fe7.5E10Na/Al₂O₃	M	0.25M	0.5M	0
10Fe10E10Na/Al₂O₃	M	0.5M	0.5M	0
10Fe10E15Na/Al₂O₃	M	0.25M	0.75M	0
10Fe10E20Na/Al₂O₃	M	0	M	0

催化剂	水溶液	pH
10Fe/Al₂O₃	Fe（NO₃）₃	0.02
10Fe10E/Al₂O₃	Fe（NO₃）₃+EDTA	-0.63
10Fe10Na/Al₂O₃	Fe（NO₃）₃+NaNO₃	0.01
10Fe10E10Na/Al₂O₃	Fe（NO₃）₃+EDTA+EDTA-2Na	-0.62

催化剂	CO吸附量/μmol·g^-1
10Fe/Al₂O₃	1.44
10Fe2.5E/Al₂O₃	1.45
10Fe5E/Al₂O₃	1.55
10Fe7.5E/Al₂O₃	1.62
10Fe10E/Al₂O₃	1.71

催化剂	CO转化率/%	CO₂选择性/%	烃类选择性/%					总选择性/%	O/P
催化剂	CO转化率/%	CO₂选择性/%	CH₄	C₂~C $_{4}^{0}$	C₂~C $_{4}^{=}$	C₅~C₁₁	C $_{12}^{+}$	总选择性/%	O/P
10Fe10Na/Al₂O₃	56.5	36.4	11.2	6.0	25.8	43.8	13.2	69.6	4.3
10Fe5E10Na/Al₂O₃	73.5	39.9	11.7	4.6	23.8	46.1	13.8	69.9	5.2
10Fe7.5E10Na/Al₂O₃	77.6	34.7	10.9	6.1	23.1	44.8	15.1	67.9	3.8
10Fe10E10Na/Al₂O₃	88.5	36.3	9.7	5.0	24.8	46.4	14.1	71.2	5.0

催化剂	CO转化率/%	CO₂选择性/%	烃类选择性/%					总选择性/%	O/P
催化剂	CO转化率/%	CO₂选择性/%	CH₄	C₂~C $_{4}^{0}$	C₂~C $_{4}^{=}$	C₅~C₁₁	C $_{12}^{+}$	总选择性/%	O/P
10Fe10Na/Al₂O₃	56.5	36.4	11.2	6.0	25.8	43.8	13.2	69.6	4.3
10Fe5E10Na/Al₂O₃	73.5	39.9	11.7	4.6	23.8	46.1	13.8	69.9	5.2
10Fe7.5E10Na/Al₂O₃	77.6	34.7	10.9	6.1	23.1	44.8	15.1	67.9	3.8
10Fe10E10Na/Al₂O₃	88.5	36.3	9.7	5.0	24.8	46.4	14.1	71.2	5.0

催化剂	CO吸附量/μmol?g^-1
10Fe10Na/Al₂O₃	1.69
10Fe10E5Na/Al₂O₃	1.54
10Fe10E10Na/Al₂O₃	1.76
10Fe10E15Na/Al₂O₃	1.97
10Fe10E20Na/Al₂O₃	2.29

催化剂	ICP		BET比表面积 /m²?g^-1	总孔容 /cm³?g^-1	孔径 /nm
催化剂	铁负载量（质量分数）/%	钠负载量（质量分数）/%	BET比表面积 /m²?g^-1	总孔容 /cm³?g^-1	孔径 /nm
Al₂O₃	—	—	147	0.89	31.3
10Fe/Al₂O₃	9.1	—	123	0.59	17.7
10Fe10E/Al₂O₃	9.0	—	137	0.54	17.7
10Fe10Na/Al₂O₃	8.8	3.6	118	0.62	17.5
10Fe10E10Na/Al₂O₃	8.9	3.8	155	0.40	18.1

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