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-NH3) 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-NH3 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 cm3/gcat.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.