新型Lewis固体酸Ce3+-Ti4+-SO42-/MWCNTs制备及催化酯化反应合成生物柴油性能研究

舒庆; 侯小鹏; 唐国强; 余长林; 王金福

新型Lewis固体酸Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs制备及催化酯化反应合成生物柴油性能研究

舒庆^{1, 2, ,},
侯小鹏¹,
唐国强¹,
余长林¹,
王金福²

1.
江西理工大学冶金与化学工程学院, 江西赣州 341000
2.
清华大学化工系, 北京 100084

基金项目:

国家自然科学基金 21206062

国家自然科学基金 21466013

江西省自然科学（青年）基金计划重大项目 20143ACB21018

化学工程联合国家重点实验室（清华大学）开放课题基金 Tsinghua University, SKL-chE-14A04

华中科技大学大型电池关键材料与系统教育部重点实验室开放课题基金 201504

详细信息

通讯作者:
舒庆, Tel:0797-8312204, E-mail:shuqing@jxust.edu.cn

中图分类号: TQ645.8
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- 文章访问数: 80
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- 被引次数: 0
出版历程
- 收稿日期: 2016-08-16
- 修回日期: 2016-11-04
- 网络出版日期: 2021-01-23
- 刊出日期: 2017-01-10

Preparation of a novel solid Lewis acid Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs and its application in the synthesis of biodiesel from esterification reaction

1.
School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
2.
Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

Funds:

National Natural Science Foundation of China 21206062

National Natural Science Foundation of China 21466013

Major Project of Natural Science Foundation of Jiangxi Province for Youth 20143ACB21018

Open Project Program of National United Key Laboratory of Chemical Engineering Tsinghua University, SKL-chE-14A04

and Open Project Program of Key Laboratory for Large-Format Battery Materials and System of Huazhong University of Science and Technolog 201504

摘要

摘要: 采用高温浸渍法，通过Ce³⁺、Ti⁴⁺和浓硫酸磺化反应对多壁纳米碳管进行了改性处理，制备了Lewis酸型固体酸催化剂Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs，并采用透射电镜、拉曼光谱、X射线光电子能谱、吡啶吸附红外光谱、X射线荧光光谱、X射线衍射光谱和NH₃程序升温脱附等多种测试技术对催化剂的物理化学特性和结构特征进行了表征。以Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs为油酸与甲醇经酯化反应合成生物柴油的催化剂，对其催化性能进行了研究。结果表明，当醇油物质的量比为12：1，催化剂与反应物质量比为1%，反应温度为65℃，反应5 h，油酸转化率为93.4%。催化剂Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs在重复使用八次后，油酸的转化率仍为80.8%，由此表明其具有较高的催化活性和稳定性。高催化活性和稳定性是因为，纳米碳管的C 1s结合能较一般炭材料低，使得电子在其管状结构中的流动和逃逸非常容易，从而有助于负载于纳米碳管之上的活性组分之间发生强烈的相互作用，最终促使Ce³⁺和Ti⁴⁺分别与SO₄^2-形成稳定的配位键，增大催化剂的晶化程度，并使SO₄^2-与纳米碳管结合的更加牢固，增强了催化剂的稳定性，减少了催化剂中活性组分的流失。最后，由于SO₄^2-与Ce³⁺的强相互作用，在不增加纳米碳管表面缺陷的情况下，改变了Ti⁴⁺-SO₄^2-中表面原子的化学状态，使得S⁶⁺离子和Ti⁴⁺离子的吸电子能力增加，使催化剂以Lewis酸性活性位为主，避免了SO₄^2-/MWCNTs因为以Brönsted酸位为主，而在富含水的反应介质中，由于水合反应而降低其催化活性的现象发生。
- 生物柴油 /
- 多壁纳米碳管 /
- Lewis酸型固体酸 /
- 酯化反应 /
- 配位键
Abstract: The Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs catalyst was prepared from the modification treatment of multi walled carbon nanotubes by concentrated sulfuric acid, Ce³⁺ and Ti⁴⁺ through the employing of high temperature impregnation method. Physicochemical properties and structural characteristics of the obtained-catalysts were characterized by means of transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, pyridine adsorption FT-IR spectra, X-ray fluorescence spectroscopy, X-ray diffraction and NH₃ temperature programmed desorption. The catalytic activity of Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs for the synthesis of biodiesel from the esterification of methanol and oleic acid was investigated. The influence of SO₄^2-/MWCNTs, which was resulted from the addition of Ce³⁺ and Ti⁴⁺, on the structure and catalytic activity was cleared based on the above structure characterization and catalytic activity investigation. The results showed that the conversion of oleic acid reached 93.4% after 5 h reaction at 65℃, when the catalyst/reactants was 1% and the molar ratio of methanol/oleic acid was 12:1. The conversion of oleic acid was 80.8% after the Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs were cycled for eight times. Therefore, it can be concluded that this catalyst has high catalytic activity and stability. The high catalytic activity and stability can be explained as follows:the C 1s binding energy of carbon nanotube is much lower than other carbon materials, resulting in easy flow and escape of the electrons in the tubular structure. Thus, the strong interactions will occur among the active groups that have been loaded on the carbon nanotube, which impels Ce³⁺ and Ti⁴⁺ to respectively form stable coordination bonds with SO₄^2-, increases the crystallization degree of the Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs catalyst and the active acid sites without increasing the surface defects, and the combination of SO₄^2- and MWCNTs was more stable. In addition, the chemical state of surface atom on the Ti-SO₄^2- was changed due to the strong interaction between SO₄^2- and Ce³⁺, which strengthened the electron withdrawing ability of S⁶⁺ and Ti⁴⁺ ions and enhanced the acidity strength of Lewis acid with changing of the acid type. Hence, the Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs will be composed by Lewis acid sites mainly, which is favorable for avoiding the occurrence of hydration of acid active sites for the SO₄^2-/MWCNTs catalyst because it was composed of Brönsted acid sites mainly.
- biodiesel /
- carbon nanotube /
- solid Lewis Acid /
- esterification /
- coordination bond

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图 1 MWCNTs、SO₄^2-/MWCNTs、Ti⁴⁺-SO₄^2-/MWCNTs和Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs的XRD谱图

Figure 1 XRD patterns of MWCNTs, SO₄^2-/MWCNTs, Ti⁴⁺-SO₄^2-/MWCNTs and Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs

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图 2 Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs、Ti⁴⁺-SO₄^2-/MWCNTs、SO₄^2-/MWCNTs和MWCNTs的拉曼光谱谱图

Figure 2 Raman spectra of Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs, Ti⁴⁺-SO₄^2-/MWCNTs, SO₄^2-/MWCNTs and MWCNTs

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图 3 SO₄^2-/MWCNTs (a), (d)、Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs (b), (e)和Ti⁴⁺-SO₄^2-/MWCNTs (c), (f)透射电镜照片

Figure 3 TEM images of SO₄^2-/MWCNTs (a), (d), Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs (b), (e) and Ti⁴⁺-SO₄^2-/MWCNTs (c), (f)

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图 4 SO₄^2-/MWCNTs (a)、Ti⁴⁺-SO₄^2-/MWCNTs (b)和催化剂Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs (c)在473 K时的吡啶红外光谱谱图

Figure 4 FT-IR spectra of adsorbed pyridine after desorption at 473 K for SO₄^2-/MWCNTs (a), Ti⁴⁺-SO₄^2-/MWCNTs (b) and Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs (c)

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图 5 SO₄^2-/MWCNTs (a)、Ti⁴⁺-SO₄^2-/MWCNTs (b)和催化剂Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs (c)的NH₃程序升温脱附谱图

Figure 5 NH₃ temperature-programmed desorption profiles of SO₄^2-/MWCNTs (a), Ti⁴⁺-SO₄^2-/MWCNTs (b) and Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs (c)

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图 6 催化剂Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs的X射线光电子能谱谱图

Figure 6 X-ray photoelectron spectroscopy of Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs

(a): C 1s; (b): Ce 3d; (c): S 2p; (d): Ti 2p

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图 7 催化剂Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs的Lewis酸位形成机理示意图

Figure 7 Formation mechanism of Lewis acid sites in Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs

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图 8 SO₄^2-/MWCNTs、Ti⁴⁺-SO₄^2-/MWCNTs、Ce³⁺-SO₄^2-/MWCNTs、Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs的催化酯化反应活性比较

Figure 8 Comparison of catalytic activity of SO₄^2-/MWCNTs, Ti⁴⁺-SO₄^2-/MWCNTs, Ce³⁺-SO₄^2-/MWCNTs, Ce³⁺-Ti⁴⁺-SO₄^2- /MWCNTs in the esterification

reaction conditions: mass ratio of catalyst to reactants is 0.5%, the mol ratio of methanol to oleic acid is 12: 1, reaction temperature is 65 ℃

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图 9 反应温度对油酸转化率的影响

Figure 9 Influence of reaction temperature on the conversion of oleic acid

reaction conditions: mass ratio of catalyst to reactants is 0.5%, the mol ratio of methanol to oleic acid is 12: 1, reaction time is 7 h

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图 10 催化剂用量对油酸转化率的影响

Figure 10 Influence of catalyst loading on the conversion of oleic acid

reaction conditions: the reaction temperature is 65 ℃, the mol ratio of methanol to oleic acid is 12: 1, reaction time is 7 h

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图 11 甲醇与油酸的物质的量比对油酸转化率的影响

Figure 11 Influence of mol ratio of methanol/oleic acid on the conversion of oleic acid

reaction conditions: the reaction temperature is 65 ℃, the mass ratio of catalyst to reactants is 1%, reaction time is 7 h

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图 12 SO₄^2-/MWCNTs、Ti⁴⁺-SO₄^2-/MWCNTs和Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs的催化稳定性比较

Figure 12 Comparison of the catalytic stability of SO₄^2-/MWCNTs, Ti⁴⁺-SO₄^2-/MWCNTs and Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs

reaction conditions: the reaction temperature is 65 ℃, the mass ratio of catalyst to reactants is 1%, reaction time is 5 h

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