基于LiAl-LDH/C杂化前体制备高比表面固体碱催化剂及其催化性能研究

doi:10.11949/0438-1157.20201682

摘要/Abstract

摘要：

采用成核-晶化隔离法制备LiAl-CO₃-LDHs晶核，在LDHs晶核晶化的过程中引入葡萄糖分子作为碳源，构筑组成和结构可调的LDHs/C型杂化复合前体。通过高温处理，实现前体的结构拓扑转变及无定形碳组分的去除，得到高比表面积的LiAl复合金属氧化物型固体碱催化剂。采用XRD、FT-IR、BET、TEM、SEM、CO₂-TPD等表征手段对催化剂的组成、结构、织构性能、表面碱性进行了详细研究，并以苯甲醛和氰基乙酸乙酯间的Knoevenagel缩合反应为探针反应系统地研究了催化剂的碱催化性能。研究结果表明，LDHs/C杂化前体制备过程中葡萄糖与金属离子的摩尔比、水热晶化温度以及焙烧温度是影响催化剂活性的主要因素，晶化温度和焙烧温度的提升不利于碱性位的充分暴露。在150℃的水热晶化温度下，葡萄糖与Al³⁺的摩尔比为3时的杂化复合前体经500℃焙烧得到的LiAl-MMO-150-3-500固体催化剂比表面积高达229 m²·g^-1，苯酚吸附测得催化剂的总碱量为855 μmol·g^-1，对苯甲醛的转化率高达88.21%。

关键词: 层状双金属氢氧化物, 杂化前体, 高比表面积, 固体碱催化剂, Knoevenagel缩合反应

Abstract:

A series of LiAl-CO₃-LDH/C hybrid composite precursors were prepared by a novel separate nucleation and aging steps we developed previously, glucose molecules were introduced as carbon source during the crystallization process of LDHs nuclei to fabricate LDHs/C hybrid composite precursor with controlled composition and structure. LiAl composite oxide based solid base catalyst with high specific surface area was obtained by topological transformation of precursors and removal of amorphous carbon components under high temperature treatment. Using XRD, FT-IR, BET, TEM, SEM, CO₂-TPD and other characterization methods, the composition, structure, texture properties and surface basicity of the catalyst were studied in detail. Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate was used as the probe reaction to investigate the alkali catalytic performance of the prepared catalyst. The results indicate that molar ratio of glucose to Al³⁺, hydrothermal temperature and calcination temperature are the main factors affecting the activity of catalysts, and higher hydrothermal temperature or calcination temperature has negative impact on the exposure of basic sites. The LiAl-MMO-150-3-500 catalyst, calcinated at 500℃ with the molar ratio of glucose to Al³⁺ was 3 in the corresponding precursor, has a surface area of about 229 m²·g^-1, the total basic sites of about 855 μmol·g^-1 based on phenol adsorption method, and thus exhibits the highest catalytic performance with the conversion of benzaldehyde reach up to 88.21% under our experimental conditions.

Key words: layered double hydroxides, hybrid precursor, high specific surface areas, solid base catalyst, Knoevenagel condensation reaction

中图分类号:

TQ 131.1

宋奕慧, 雷志轶, 范国利, 杨兰, 林彦军, 李峰. 基于LiAl-LDH/C杂化前体制备高比表面固体碱催化剂及其催化性能研究[J]. 化工学报, 2021, 72(6): 3084-3094.

SONG Yihui, LEI Zhiyi, FAN Guoli, YANG Lan, LIN Yanjun, LI Feng. Preparation and property of high specific surface solid base catalyst based on LiAl-LDH /C hybrid precursor[J]. CIESC Journal, 2021, 72(6): 3084-3094.

图/表 14

图1 不同条件下制备得到的LiAl-LDHs-x-y杂化复合前体的XRD谱图a— LiAl-LDHs-150-0; b—LiAl-LDHs-150-1; c—LiAl-LDHs-150-3; d—LiAl-LDHs-150-4; e—LiAl-LDHs-160-3; f—LiAl-LDHs-180-3

Fig.1 XRD patterns of LiAl-LDHs-x-y prepared at different conditions

表1 不同条件下制备的LiAl-LDHs-x-y的XRD数据

Table 1 XRD parameters of LiAl-LDHs-x-y prepared at different conditions

Samples	hkl	d / nm	a / nm	c / nm	D_a / nm	D_c / nm
LiAl-LDHs-150-0	(003) (110)	0.7360 0.1466	0.2932	2.208	35.37	30.26
LiAl-LDHs-150-1	(003) (110)	0.7725 0.1474	0.2948	2.318	14.41	6.994
LiAl-LDHs-150-3	(003) (110)	0.7583 0.1471	0.2942	2.2749	12.82	5.567
LiAl-LDHs-150-4	(003) (110)	0.7730 0.1475	0.2950	2.319	19.21	4.503
LiAl-LDHs-160-3	(003) (110)	0.7814 0.1530	0.3060	2.344	13.39	5.932
LiAl-LDHs-180-3	(003) (110)	0.7729 0.1521	0.3042	2.319	17.07	6.222

图2 系列LiAl-LDHs-150-y的红外谱图a—LiAl-LDHs-150-0; b—LiAl-LDHs-150-1; c—LiAl-LDHs-150-3; d—LiAl-LDHs-150-4

Fig.2 FT-IR spectra of series LiAl-LDHs-150-y prepared at different conditions

图3 不同条件下得到的系列LiAl-MMO-150-y-z的XRD谱图a—LiAl-MMO-150-0-500; b—LiAl-MMO-150-1-500; c—LiAl-MMO-150-3-500; d—LiAl-MMO-150-4-500; e—LiAl-MMO-150-3-400; f—LiAl-MMO-150-3-700

Fig.3 XRD patterns of LiAl-MMO-150-y-z prepared at different conditions

图4 系列LiAl-MMO-150-y-500样品的红外谱图a—LiAl-MMO-150-0-500; b—LiAl-MMO-150-1-500; c—LiAl-MMO-150-3-500; d—LiAl-MMO-150-4-500

Fig.4 FT-IR spectra of series LiAl-MMO-150-y-500 samples

图5 LiAl-LDHs-150-0样品的TG-DTA-MS谱图

Fig.5 TG-DTA-MS profiles of LiAl-LDHs-150-0 sample

图6 系列LiAl-MMO-150-y-500样品的TEM图

Fig.6 TEM images of series LiAl-MMO-150-y-500 samples

图7 系列LiAl-MMO-x-y-z样品的SEM图

Fig.7 SEM images of series LiAl-MMO-x-y-z

图8 系列LiAl-MMO-x-y-z的N2吸-脱附等温线a—LiAl-MMO-150-0-500; b—LiAl-MMO-150-1-500; c—LiAl-MMO-150-3-500; d—LiAl-MMO-150-4-500; e—LiAl-MMO-180-3-500; f—LiAl-MMO-150-3-700; g—LiAl-MMO-160-3-500; h—LiAl-MMO-150-3-400

Fig.8 N2 adsorption-desorption isotherms of series LiAl-MMO-x-y-z

表2 系列LiAl-MMO-x-y-z的比表面积和孔径分布参数

Table 2 Specific surface areas and pore distribution parameters of series of LiAl-MMO-x-y-z samples

Samples	Specific area/(m²·g^-1)	Total volume/(ml·g^-1)	Optimum pore size/nm
LiAl-MMO-150-0-500	123	0.2170	3.9
LiAl-MMO-150-1-500	225	1.0168	14.0
LiAl-MMO-150-3-500	229	0.8962	7.2
LiAl-MMO-150-4-500	241	1.2230	12.0
LiAl-MMO-160-3-500	206	0.5393	9.7
LiAl-MMO-180-3-500	178	1.0440	9.5
LiAl-MMO-150-3-400	232	0.9421	65
LiAl-MMO-150-3-700	94	0.6095	20.1

图9 系列LiAl-MMO-x-y-z的CO2-TPD曲线a—LiAl-MMO-150-0-500; b—LiAl-MMO-150-1-500; c—LiAl-MMO-150-3-500; d—LiAl-MMO-150-4-500; e—LiAl-MMO-180-3-500; f—LiAl-MMO-150-3-700; g—LiAl-MMO-160-3-500; h—LiAl-MMO-150-3-400

Fig.9 CO2-TPD curves of series LiAl-MMO-x-y-z

图10 系列LiAl-MMO-x-y-z的苯酚吸附等温线a—LiAl-MMO-150-0-500; b—LiAl-MMO-150-1-500; c—LiAl-MMO-150-3-500; d—LiAl-MMO-150-4-500; e—LiAl-MMO-180-3-500; f—LiAl-MMO-150-3-700; g—LiAl-MMO-160-3-500; h—LiAl-MMO-150-3-400

Fig.10 Phenol adsorption isotherms of series LiAl-MMO-x-y-z

表3 系列LiAl-MMO-x-y-z的碱性参数

Table 3 Basic sites data of series of LiAl-MMO-x-y-z

Samples	Number of base sites/(μmol of phenol·g^-1)	Density of base sites/(μmol of phenol·m^-2)
LiAl-MMO-150-0-500	306	2.49
LiAl-MMO-150-1-500	635	2.82
LiAl-MMO-150-3-500	855	3.74
LiAl-MMO-150-4-500	800	3.32
LiAl-MMO-160-3-500	730	3.54
LiAl-MMO-180-3-500	635	3.57
LiAl-MMO-150-3-400	582	2.51
LiAl-MMO-150-3-700	308	3.28

图11 系列LiAl-MMO-x-y-z的催化性能曲线a—LiAl-MMO-150-0-500; b—LiAl-MMO-150-1-500; c—LiAl-MMO-150-3-500; d—LiAl-MMO-150-4-500; e—LiAl-MMO-180-3-500; f—LiAl-MMO-150-3-700; g—LiAl-MMO-160-3-500; h—LiAl-MMO-150-3-400

Fig.11 Catalytic performance of series LiAl-MMO-x-y-z

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