结晶度
催化作用
材料科学
结晶
空间速度
ZSM-5型
傅里叶变换红外光谱
化学工程
酸强度
热液循环
甲醇
沸石
核化学
选择性
化学
有机化学
复合材料
工程类
作者
Parisa Sadeghpour,Mohammad Haghighi,Mehrdad Esmaeili
出处
期刊:Combinatorial Chemistry & High Throughput Screening
[Bentham Science]
日期:2021-01-01
卷期号:24 (4): 490-508
被引量:3
标识
DOI:10.2174/1386207323666200825144543
摘要
Aim and Objective: The effect of two different modification methods for introducing Ni into the ZSM-5 framework was investigated under high-temperature synthesis conditions. The nickel was successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. Materials and Methods: A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM- 5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BETBJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPD-NH 3 ) were applied to investigate the physicochemical properties. Results: Although all the catalysts showed pure silica MFI–type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced the more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH 3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm 3 /g cat .h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. Conclusion: The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.
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