Incorporation of Cr in ZSM-5 zeolite framework as bifunctional catalysts for n-butane catalytic cracking

doi:10.11949/j.issn.0438-1157.20160459

Abstract

Abstract:

The Cr-doped ZSM-5 zeolites were synthesized by in-situ hydrothermal method and were used in studying Cr effect on catalytic cracking of n-butane to produce light olefins. Zeolite structure, chemical state of Cr species and acidity of zeolites were characterized by several techniques, including X-ray diffraction, nitrogen adsorption and desorption, ultraviolet visible diffuse reflectance spectroscopy, Raman spectroscopy, ammonia temperature-programmed desorption and pyrrolidine (Py)-FTIR. Cr species were found to partially incorporate in the ZSM-5 framework and present in the form of monodispersion. No significant difference in the weak acidity of zeolites at low Cr content. However, a small amount of Cr species in zeolites could significantly enhance conversion of n-butane and improve yield of ethylene and propylene. When the molar ratio of Cr/Al was 0.04, the conversion of n-butane was 99.6% and the yield of ethylene and propylene was 53.8% at reaction temperature of 650℃, which was 15.5% and 5.0% higher than those of unmodified ZSM-5, respectively. The superior catalytic performance could be attributed to synergistic effects of dehydrogenation of active Cr species and cracking function of the acidic zeolite, which promoted highly efficient conversion of n-butane.

Key words: Cr doping, ZSM-5 zeolites, bifunctionality, catalytic cracking, light olefins

摘要：

采用原位合成的方法制备了Cr掺杂的ZSM-5分子筛，研究了Cr含量对于正丁烷催化裂解性能的影响。利用X射线衍射（XRD）、N₂吸附脱附、紫外可见漫反射光谱（UV-Vis）、拉曼光谱（Raman）、氨程序升温脱附技术（NH₃-TPD）和吡啶红外（Py-FTIR）等表征手段研究了分子筛的结构、Cr物种的存在状态以及分子筛的酸性。研究结果表明，部分Cr进入分子筛的骨架，以单分散的形式存在，当Cr含量较低时，Cr的引入对于分子筛的弱酸性没有太大的影响。少量Cr的引入会极大提高正丁烷的转化率和乙烯、丙烯的收率，当Cr/Al摩尔比为0.04，反应温度为650℃时，正丁烷的转化率达到99.2%，乙烯、丙烯的收率达到53.8%，分别比未改性的ZSM-5高15.5%和5.0%。这可能是由于Cr活性组分的脱氢性能和分子筛的酸性形成协同作用，促进了正丁烷的高效转化。

关键词: Cr掺杂, ZSM-5分子筛, 双功能, 催化裂解, 低碳烯烃

CLC Number:

O643.3

ZHAO Dan, YUAN Meihua, ZHANG Yaoyuan, JIANG Guiyuan, ZHAO Zhen, LIU Jia, HAN Shanlei, SUN Huaqian. Incorporation of Cr in ZSM-5 zeolite framework as bifunctional catalysts for n-butane catalytic cracking[J]. CIESC Journal, 2016, 67(8): 3400-3407.

赵丹, 袁美华, 张耀远, 姜桂元, 赵震, 刘佳, 韩善磊, 孙华倩. Cr掺杂ZSM-5双功能催化剂的制备及其催化裂解正丁烷[J]. 化工学报, 2016, 67(8): 3400-3407.

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