掺杂改性对钙铝基复合物酯交换催化剂吸附性能影响的分子模拟

doi:10.11949/0438-1157.20200357

摘要/Abstract

摘要：

借助分子模拟手段，研究了锌、镧、镁掺杂改性对钙铝基复合型金属氧化物催化酯交换的影响。构建了Al₂O₃(110)、CaO(100)以及锌、镧、镁掺杂改性的衍生模型。计算了不同改性氧化铝表面的掺杂结合能，分析了甲醇和乙酸甲酯在氧化钙及其衍生物表面的吸附过程，讨论了甲醇在Al₂O₃(110)及其衍生物表面的吸附过程及其Mulliken电荷密度的变化。结果表明，采用锌、镧、镁掺杂改性能强化钙铝复合型金属氧化物催化剂对甲醇的吸附性能，有助于催化酯交换反应的进行。

关键词: 生物柴油, 钙铝二元复合物催化剂, 吸附, 掺杂改性, 分子模拟

Abstract:

With the help of molecular simulations, the effect of zinc, lanthanum and magnesium doping modification on the transesterification catalyzed by calcium-aluminum composite catalyst was studied. The model for Al₂O₃(110) and CaO(100) surfaces were constructed and a series of derivative models doped by zinc, lanthanum, and magnesium were then obtained. Doping binding energy of various doped Al₂O₃(110) surfaces were calculated. The adsorption process of methanol and methyl acetate on CaO(100) and its derivative surfaces were analyzed. The adsorption process of methanol on Al₂O₃(110) and its derivative surfaces and the Mulliken charge density change were discussed. The results show that the calcium-aluminum composite catalysts doped with zinc, lanthanum, and magnesium can enhance the adsorption performance for methanol, which contribute a lot to catalyzing transesterification reaction.

Key words: biodiesel, calcium-aluminum binary composite catalyst, adsorption, doped modification, molecular simulation

中图分类号:

TK 6

厉志鹏, 牛胜利, 韩奎华, 路春美. 掺杂改性对钙铝基复合物酯交换催化剂吸附性能影响的分子模拟[J]. 化工学报, 2020, 71(8): 3625-3632.

Zhipeng LI, Shengli NIU, Kuihua HAN, Chunmei LU. Molecular simulation of the effect of doping modification on the adsorption properties of calcium-aluminum-based composites ester exchange catalysts[J]. CIESC Journal, 2020, 71(8): 3625-3632.

图/表 11

图1 甲醇结构和乙酸甲酯结构(红色为氧原子，白色为氢原子，灰色为碳原子)

Fig.1 Structure of methanol and methyl acetate (O atoms are red, H atoms are white and C atoms are gray)

表1 甲醇和乙酸甲酯的键长

Table 1 Bond length of methanol and methyl acetate

分子	键	键长/ nm
分子	键	本文	文献^[4,20]
甲醇	O—H	0.097	0.096
	C—O	0.143	0.143
	C—H_1/2/3	0.109/0.110/0.110	0.110/0.110/0.110
乙酸甲酯	C—O_1/2	0.144/0.136	0.143/0.136
	C—C	0.150	0.150
	CO	0.122	0.122
	C—H_1/2/3	0.109/0.109/0.109	0.109/0.109/0.109
	C—H_4/5/6	0.109/0.110/0.110	0.109/0.109/0.109

图2 γ-Al2O3(110)结构表面（红色为氧原子，粉色为铝原子）

Fig.2 Structure of the γ-Al2O3(110) surface(O atoms are red and Al atoms are pink)

表2 催化剂表面在不同情况下的掺杂结合能

Table 2 Dopant incorporation energy of catalysts surface under different conditions

掺杂方式	掺杂结合能（kJ/mol）
掺杂方式	Ca, M=0	Ca, M=Zn	Ca, M=La	Ca, M=Mg
Ca 取代 Al_3c-1, M 取代 Al_5c-1	215.03 215.03	969.33	151.23	652.17
Ca 取代 Al_3c-1, M 取代 Al_4c-1	215.03 215.03	982.20	284.34	688.67
Ca 取代 Al_4c-1, M 取代 Al_3c-1	294.06 294.06	1037.07	310.07	728.05
Ca 取代 Al_4c-1, M 取代 Al_5c-1	294.06 294.06	893.98	228.42	721.49
Ca 取代 Al_5c-1, M 取代 Al_4c-1	214.50 214.50	970.12	242.60	676.59
Ca 取代 Al_5c-1, M 取代 Al_3c-1	214.50 214.50	960.15	213.98	643.25

图3 掺杂改性后催化剂表面结构俯视图（红色为氧原子，粉色为铝原子，绿色为钙原子，黄色为镁原子，黑色为锌原子，蓝色为镧原子）

Fig.3 Top view of doped catalyst structure surfaces (O atoms are red, Al atoms are pink, Ca atoms are green, Mg atoms are yellow, Zn atoms are black and La atoms are blue)

图4 甲醇分子在Ca-M催化剂表面上的吸附构型

Fig.4 Structure of methanol molecule absorbed on Ca-M catalyst surfaces

表3 甲醇吸附在催化剂表面后的键长和吸附能

Table 3 Bond length and adsorption energy of methanol absorbed on catalyst surfaces

吸附位置	H—O键长/nm	H—M键长/nm	吸附能/ (kJ/mol)
钙催化剂表面	0.140	0.107	-137.051
钙锌催化剂表面	0.151	0.103	-164.094
钙镧催化剂表面	0.149	0.104	-136.001
钙镁催化剂表面	0.148	0.105	-158.318

表4 乙酸甲酯吸附在Ca-M催化剂表面后的键长和吸附能

Table 4 Bond length and adsorption energy of methyl acetate absorbed on Ca-M catalyst surfaces

吸附位置	CO键长/nm	吸附能/(kJ/mol)
钙催化剂表面	0.123	-120.640
钙锌催化剂表面	0.123	-135.102
钙镧催化剂表面	0.128	-149.694
钙镁催化剂表面	0.122	-100.801

图5 甲醇分子在Ca-Al-M催化剂表面的吸附

Fig.5 Structure of methanol molecule absorbed on Ca-Al-M catalyst surfaces

表5 甲醇吸附在Ca-Al-M催化剂表面后的键长和吸附能

Table 5 Bond length and adsorption energy of methanol absorbed on Ca-Al-M catalyst surfaces

吸附位置	H—O键长/nm	吸附能/(kJ/mol)
钙铝催化剂表面	0.097	-105.020
钙铝锌催化剂表面	0.098	-122.873
钙铝镧催化剂表面	0.098	-147.816
钙铝镁催化剂表面	0.098	-259.662

表6 甲醇吸附在Ca-Al-M催化剂表面的Mulliken电荷布局

Table 6 Mulliken atomic charge populations for methanol adsorption on Ca-Al-M catalyst surfaces

吸附位置	Mulliken电荷/e
吸附位置	H_(O-H)	O	C	H₁	H₂	H₃	总计
纯甲醇	0.253	-0.507	0.145	0.029	0.029	0.050	0
钙铝催化剂表面	0.327	-0.601	-0.018	0.105	0.115	0.119	0.047
钙铝锌催化剂表面	0.379	-0.623	-0.029	0.100	0.110	0.126	0.063
钙铝镧催化剂表面	0.405	-0.635	-0.024	0.108	0.113	0.124	0.091
钙铝镁催化剂表面	0.353	-0.596	-0.051	0.111	0.115	0.121	0.053

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