CH3COONa处理HZSM-5分子筛及其催化性能

doi:10.15541/jim20180336

摘要/Abstract

摘要：

采用不同浓度的CH₃COONa溶液和常规碱(NaOH和Na₂CO₃)溶液处理HZSM-5分子筛, 对处理前后的HZSM-5分子筛负载Pt, 制备Pt/HZSM-5催化剂用于丙烷脱氢反应。利用X射线衍射(XRD)、X射线荧光光谱(XRF)、扫描电镜(SEM)、比表面测试仪(BET)、NH₃-TPD(程序升温脱附法)和H₂化学吸附等手段对处理前后的HZSM-5分子筛进行表征, 并考察了不同浓度的CH₃COONa溶液和常规碱溶液处理对HZSM-5分子筛的晶体结构、表面形貌、孔结构、表面酸性及丙烷脱氢性能的影响。结果表明, CH₃COONa溶液具有碱改性作用, 与常规碱溶液相比, 采用CH₃COONa溶液处理HZSM-5分子筛, 能够在对分子筛的晶体结构和表面形貌影响较小的基础上有效地引入介孔结构, 具有较好的可调控性; 随着CH₃COONa溶液浓度的增加, 丙烷脱氢反应的丙烷初始转化率和丙烯选择性先升高后降低, 当CH₃COONa溶液浓度为4.0 mol/L时, 丙烷初始转化率和丙烯选择性均达到最高值, 分别为34.5%和98.9%。

关键词: HZSM-5, 碱处理, 丙烷脱氢

Abstract:

HZSM-5 zeolites were treated by CH₃COONa solution with different concentrations and conventional alkali (NaOH or Na₂CO₃) solution. Then, Pt was loaded on HZSM-5 zeolites before and after the treatment to synthesize Pt/HZSM-5 catalysts for propane dehydrogenation reaction. HZSM-5 zeolites were characterized by XRD, XRF, SEM, BET, NH₃-TPD, and H₂chemisorption. The effect of CH₃COONa solution with different concentrations and conventional alkali solution on crystal structure, surface morphology, pore structure, surface acidity, and propane dehydrogenation performance of HZSM-5 zeolites were investigated. The results showed that CH₃COONa solution modified HZSM-5 zeolites by alkali. Compared with conventional alkali solution, the treatment of CH₃COONa solution for HZSM-5 zeolites could more effectively introduce and better controllably the mesoporous structure with less influence on the crystal structure and surface morphology. With increase of the concentration of CH₃COONa solution, the initial propane conversion and the propene selectivity in propane dehydrogenation firstly increased and then decreased. The catalyst treated by 4.0 mol/L CH₃COONa solution exhibited the highest propane initial conversion and propene selectivity, which were 34.5% and 98.9%, respectively.

Key words: HZSM-5, alkali treatment, propane dehydrogenation

中图分类号:

TQ630

徐国皓, 余金鹏, 徐华胜, 李春成, 黄金花, 王鹏飞. CH₃COONa处理HZSM-5分子筛及其催化性能[J]. 无机材料学报, 2019, 34(5): 546-552.

Guo-Hao XU, Jin-Peng YU, Hua-Sheng XU, Chun-Cheng LI, Jin-Hua HUANG, Peng-Fei WANG. Catalystic Performance of HZSM-5 Zeolite Treated by CH₃COONa[J]. Journal of Inorganic Materials, 2019, 34(5): 546-552.

图/表 12

图1 碱处理前后HZSM-5分子筛的XRD图谱 a: HZSM-5(0); b: HZSM-5(CH3COONa, 2.0); c: HZSM-5(CH3COONa, 4.0); d: HZSM-5(CH3COONa, 6.0); e: HZSM-5(Na2CO3, 2.0); f: HZSM- 5(NaOH, 1.0)

Fig. 1 XRD patterns of HZSM-5 zeolites before and after alkaline treatment

表1 碱处理前后HZSM-5分子筛的相对结晶度和硅铝比

Table 1 Relative crystallinity and n(SiO2)/n(Al2O3) of HZSM-5 zeolites before and after alkali treatment

Sample	Relative crystallinity/%	n(SiO₂) /n(Al₂O₃)
HZSM-5(0)	100	100
HZSM-5(CH₃COONa, 2.0)	99	94
HZSM-5(CH₃COONa, 4.0)	97	90
HZSM-5(CH₃COONa, 6.0)	85	82
HZSM-5(Na₂CO₃, 2.0)	62	74
HZSM-5(NaOH, 1.0)	24	63

图2 碱处理前后HZSM-5分子筛的SEM照片 a: HZSM-5(0); b: HZSM-5(CH3COONa, 2.0); c: HZSM-5(CH3COONa, 4.0); d: HZSM-5(CH3COONa, 6.0); e: HZSM-5(Na2CO3, 2.0); f: HZSM-5(NaOH, 1.0)

Fig. 2 SEM images of HZSM-5 zeolites before and after alkaline treatment

图3 碱处理前后HZSM-5分子筛的N2吸附-脱附等温线 a: HZSM-5(0); b: HZSM-5(CH3COONa, 2.0); c: HZSM-5(CH3COONa, 4.0); d: HZSM-5(CH3COONa, 6.0); e: HZSM-5(Na2CO3, 2.0); f: HZSM- 5(NaOH, 1.0)

Fig. 3 N2 adsorption-desorption isotherms of HZSM-5 zeolites before and after alkaline treatment

表2 碱溶液处理对HZSM-5分子筛结构性质的影响

Table 2 Effect of alkaline treatment on structure of HZSM-5 zeolites

Sample	A_BET/(m²·g^-1)	A_ext/(m²·g^-1)	v_micro/(cm³·g^-1)	v_meso/(cm³·g^-1)	d_aver/nm
HZSM-5(0)	357.92	29.98	0.17	0.04	1.52
HZSM-5(CH₃COONa, 2.0)	366.64	74.43	0.16	0.07	2.35
HZSM-5(CH₃COONa, 4.0)	378.69	103.83	0.16	0.11	2.93
HZSM-5(CH₃COONa, 6.0)	375.72	93.98	0.15	0.14	3.26
HZSM-5(Na₂CO₃, 2.0)	372.64	85.48	0.13	0.17	3.51
HZSM-5(NaOH, 1.0)	360.23	66.25	0.08	0.28	4.67

图4 碱处理前后HZSM-5分子筛的NH3-TPD曲线 a: HZSM-5(0); b: HZSM-5(CH3COONa, 2.0); c: HZSM-5(CH3COONa, 4.0); d: HZSM-5(CH3COONa, 6.0); e: HZSM-5(Na2CO3, 2.0); f: HZSM-5(NaOH, 1.0)

Fig. 4 NH3-TPD curves of HZSM-5 zeolites before and after alkaline treatment

表3 碱处理前后HZSM-5分子筛的相对酸量

Table 3 Relative acid amount of HZSM-5 zeolites before and after alkaline treatment

Acid strength	Relative acid amount/%
Acid strength	HZSM-5(0)	HZSM-5 (CH₃COONa, 2.0)	HZSM-5 (CH₃COONa, 4.0)	HZSM-5 (CH₃COONa, 6.0)	HZSM-5 (Na₂CO₃, 2.0)	HZSM-5 (NaOH, 1.0)
Strong	100	98.17	90.83	102.25	103.47	108.15
Weak	100	98.14	90.06	101.86	103.18	107.28

图5 碱处理HZSM-5分子筛的脱硅过程

Fig. 5 Desilication process of the parent HZSM-5 zeolite during the alkali treatment

表4 碱溶液处理前后催化剂的氢吸附量和Pt分散度分析

Table 4 Analysis of hydrogen adsorption amount and Pt dispersion of catalysts before and after alkaline treatment

Catalyst	Hydrogen chemisorption/ (mL·g^-1Pt)	Bare fraction of metallic Pt/%
Pt/HZSM-5(0)	15.0	34.8
Pt/HZSM-5(CH₃COONa, 2.0)	21.7	50.4
Pt/HZSM-5(CH₃COONa, 4.0)	22.8	52.9
Pt/HZSM-5(CH₃COONa, 6.0)	22.2	51.6
Pt/HZSM-5(Na₂CO₃, 2.0)	19.5	45.2
Pt/HZSM-5(NaOH, 1.0)	16.6	38.6

图6 不同催化剂的丙烷转化率随反应时间的变化关系 ■: Pt/HZSM-5(0); ●: Pt/HZSM-5(CH3COONa, 2.0); ▲: Pt/HZSM-5 (CH3COONa, 4.0); ▼: Pt/HZSM-5(CH3COONa, 6.0) ?: Pt/HZSM-5 (Na2CO3, 2.0); ?: Pt/HZSM-5(NaOH, 1.0)

Fig. 6 Relationship between propane conversion and reaction time for different catalysts

图7 不同催化剂的丙烯选择性随反应时间的变化关系 ■: Pt/HZSM-5(0); ●: Pt/HZSM-5(CH3COONa, 2.0); ▲: Pt/HZSM-5 (CH3COONa, 4.0); ▼: Pt/HZSM-5(CH3COONa, 6.0) ?: Pt/HZSM-5 (Na2CO3, 2.0); ?: Pt/HZSM-5(NaOH, 1.0)

Fig. 7 Relationship between propene selectivity and reaction time for different catalysts

图8 丙烷脱氢反应机理示意图

Fig. 8 Schematic diagram of mechanism of dehydrogenation of propane

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CH₃COONa处理HZSM-5分子筛及其催化性能

Catalystic Performance of HZSM-5 Zeolite Treated by CH₃COONa

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