化学链甲烷氧化偶联界面反应路径和晶格氧传递的分子动力学模拟

李婉莹; 陈良勇

doi:10.1016/S1872-5813(23)60412-8

化学链甲烷氧化偶联界面反应路径和晶格氧传递的分子动力学模拟

doi: 10.1016/S1872-5813(23)60412-8

李婉莹,
陈良勇^,

东南大学能源与环境学院能源转换及其过程测控教育部重点实验室, 江苏南京 210096

基金项目: 国家自然科学基金 (52076042)资助

详细信息

通讯作者:
E-mail: 101012271@seu.edu.cn

中图分类号: TQ038
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- 被引次数: 0
出版历程
- 收稿日期: 2023-12-19
- 修回日期: 2024-01-24
- 录用日期: 2024-01-31
- 网络出版日期: 2024-02-29

Surface reaction and lattice oxygen transfer in chemical looping oxidative coupling of methane: Molecular dynamics simulations

LI Wanying,
CHEN Liangyong^,

Key Laboratory of Energy Thermal Conversion and Control, School of Energy and Environment, Southeast University, Nanjing 210096, China

Funds: The project was supported by National Natural Science Foundation of China (52076042).

摘要

摘要: 本研究采用分子动力学模拟的方法计算八种金属氧化物催化剂-载氧体CL-OCM反应性能，并对性能最优的Mn₂O₃开展反应时间和颗粒尺寸的研究。结果表明，适当延长反应时间有利于提高 C₂H₄ 选择性； C/O=1 是Mn₂O₃的理想尺寸。基于以上结果分析了Mn₂O₃ CL-OCM界面反应路径和晶格氧传递问题，以揭示反应机理。CH₃ ^*气相二聚化生成C₂H₆的是CL-OCM最主要的碳偶联路径。除此之外，还存在两条碳偶联路径，均由CH₂ ^*引发。CH₃ ^*与OH^*表面结合生成甲醇是CL-OCM副反应的先决步骤，抑制甲醇生成是提高CL-OCM反应C₂选择性的关键。晶格氧存在转化，表面晶格氧是甲烷活化的活性氧。晶格氧数量差异及体相晶格氧迁移阻力差异是导致CH₄转化率和C₂选择性不同的主要原因。该研究为CL-OCM催化剂-载氧体的机理探究提供新的方法。
- 化学链甲烷氧化偶联 /
- 催化剂-载氧体 /
- 分子动力学模拟 /
- 界面反应 /
- 晶格氧
Abstract: Chemical looping oxidative coupling of methane (CL-OCM) is a promising methodology for ethylene production from methane. This article utilizes molecular dynamic (MD) simulation to assess the performance of eight metal oxide catalytic oxygen carriers in CL-OCM reactions. It also investigates the impact of reaction time and particle size on the efficiency of the most effective Mn₂O₃COC. The results indicate that extending the reaction time appropriately enhances C₂H₄ selectivity and a C/O ratio of 1 is found to be the optimal size for Mn₂O₃-based CL-OCM. Furthermore, surface reactions and lattice oxygen transfer are analyzed by MD simulation in Mn₂O₃-based CL-OCM, providing deeply insights into the reaction mechanism. The findings reveal that the gas-phase dimerization of CH₃ ^* to form C₂H₆ serves as the primary carbon coupling pathway in CL-OCM. In addition, there are two other carbon coupling pathways, both initiated by CH₂ ^*. Methanol formation through surface combination of CH₃ ^* and OH^* represents an initial step in CL-OCM side reactions. Therefore, inhibiting methanol formation is crucial for enhancing C₂ selectivity in CL-OCM. There exists a transformation of lattice oxygen and surface lattice oxygen plays a key role in methane activation. The quantity of lattice oxygen and difference in bulk lattice oxygen migration resistance are major factors influencing variations CH₄ conversion and C₂ selectivity. This study provides a new way to reaction mechanism exploration related to CL-OCM catalytic oxygen carriers.
- chemical-looping oxidative coupling of methane /
- catalytic oxygen carrier /
- molecular dynamics simulation /
- surface reaction /
- lattice oxygen

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图 1 CL-OCM反应性能

Figure 1 Performance in CL-OCM

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图 2 （a）Mn₂O₃和（b）CuO CL-OCM界面反应碳偶联路径

Figure 2 Surface reaction network of carbon coupling for (a) Mn₂O₃ and (b) CuO CL-OCM

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图 3 Mn₂O₃ CL-OCM 关键副反应路径

Figure 3 Critical side reaction for Mn₂O₃ CL-OCM

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图 4 Mn₂O₃晶格氧分类

Figure 4 Mn₂O₃ lattice oxygen classification

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图 5 Mn₂O₃（a）表面晶格氧传递过程（b）体相晶格氧转化过程反应快照和（c）反应过程示意图

Figure 5 Mn₂O₃ (a) surface lattice oxygen transfer snapshots, (b) bulk lattice oxygen transformation snapshots and(c) reaction process diagram

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图 6 不同C/O比下Mn₂O₃ CL-OCM反应（a）甲烷转化率（b）表面晶格氧浓度（c）C₂选择性和（d）晶格氧消耗个数变化

Figure 6 The calculated (a) CH₄ conversion, (b) surface lattice oxygen concentration, (c) C₂ selectivity and (d) number of lattice oxygen consumption for CL-OCM using Mn₂O₃ COC at different C/O

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表 1 分子动力学模拟输入条件

Table 1 Molecular dynamic simulation input conditions

	Metal oxide	Time t/ps	Radius r/Å (C/O)	No.
Different metal oxides	Mn₂O₃	500	12 (1)	1
	Mn₃O₄			2
	Fe₂O₃			3
	Fe₃O₄			4
	FeO			5
	CuO			6
	Cu₂O			7
	NiO			8
Reaction time	Mn₂O₃	250	12 (1)	9
		1000		10
		2000		11
Particle size	Mn₂O₃	500	9.5 (2)	12
			13.5 (0.75)	13
			15.5 (0.5)	14

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表 2 Mn₂O₃体系 CL-OCM反应中间体和产物及其首次出现时间

Table 2 Intermediates and products and their first appearance time for CL-OCM using Mn₂O₃

Intermediate	First appearance time t/ps	Product	First appearance time t/ps
CH₃ ^*	0.025	C₂H₆	7.75
CH₂ ^*	9.575	C₂H₄	45.95
CH^*	187.625	C₂H₂	494.025
H^*	5.625	CO	44.225
O^*	0.025	CO₂	60.275
OH^*	5	H₂O	15.175
C^*	388.95	H₂	7.975
CH₃O^*	23.1	CH₂O	6.575
CHO^*	36.85	CH₃OH	3.325
C₂H₅ ^*	39.375	CH₃OCH₃	145.025
C₂H₃ ^*	67.475	CHOOH	59.9

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表 3 CuO体系CL-OCM反应中间体和产物及其首次出现时间

Table 3 Intermediates and products and their first appearance time for CL-OCM using CuO

Intermediate	First appearance time t/ps	Product	First appearance time t/ps
CH₃ ^*	0.05	C₂H₆	184.3
CH₂ ^*	0.025	C₂H₄	99.15
CH^*	29.475	C₂H₂	93.85
H^*	0.7	CO	244.75
O^*	2.675	H₂O	65.4
OH^*	4.6	H₂	142.1
CH₃O^*	32.125	CH₂O	14.8
CHO^*	72.825	CH₃OH	14.45
C₂H₅ ^*	93.775	C₃H₄	408.755
C₂H₃ ^*	150.65	−	−
C₃H₅ ^*	404.45	−	−

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表 4 CL-OCM反应过程中Mn₂O₃组分及晶格氧变化

Table 4 Changes of Mn₂O₃ composition and lattice oxygen during CL-OCM reaction

Time/ps	Composition	R_o/%	R_lo/%
0	Mn₂O₃	59.84	57.51
50	Mn₂O_2.85	58.80	47.25
100	Mn₂O_2.57	56.25	46.60
150	Mn₂O_2.29	53.41	37.94
200	Mn₂O_2.12	51.50	34.50
250	Mn₂O_2.03	49.58	31.91
300	Mn₂O_1.83	47.80	26.70
350	Mn₂O_1.74	46.52	24.74
400	Mn₂O_1.69	45.78	24.74
450	Mn₂O_1.67	45.49	24.68
500	Mn₂O_1.63	45.00	25.00

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