Characterization of zeolite-based catalysts for methane conversion

Publication Issue: 
Volume 29, Number 3&4, 2008
Page No: 
Date Received: 
Wednesday, December 26, 2007
Authors' Name: 
A. Asmadia
M. Ramlib
M. S. Azharc
H. B. Seninc
Authors' Affiliation and Address: 
aDepartment of Engineering Science, Faculty of Science and Technology, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia
bDepartment of Chemical Engineering, Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
cDepartment of Physical Sciences, Faculty of Science and Technology, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia

The direct conversion of natural gas to liquid hydrocarbons has not yet been successfully
economized in an inexpensive process. The conversions of methane to gasoline by direct
routes are still at low activity and selectivity. This process is possible if the reaction is
carried out by controlled oxidation over a suitable catalyst. The main concern is to modify
the ZSM-5 zeolite catalyst framework with suitable oxidative elements so that highly active
bifunctional oxidative-acid catalysts could be developed. The objective of this study is to
modify HZSM-5 zeolite catalyst with gallium metal by acidic ion exchange method to form
a bifunctional oxidative and acid catalyst. The obtained catalyst, Ga-HZSM-5, might act as
a better bifunctional oxidative-acid catalyst than its parent catalyst, HZSM-5 zeolite.
ZSM-5 zeolite catalyst was prepared by direct synthesis to produce HZSM-5 catalyst. The
HZSM-5 zeolite catalyst was modified by an acidic ion exchange method to produce
Ga-HZSM-5 zeolite catalyst. HZSM-5 and Ga-HZSM-5 catalysts were characterized by
X-Ray Diffraction Measurement (XRD), Nuclear Magnetic Resonance (NMR), Nitrogen
Adsorption and Temperature Programmed Desorption (TPD). The characterization results
revealed that Al ions were removed from the framework and/or replaced by Ga ions into the
parent framework. Some of the metal oxides also covered the internal surface of the pores
or channels of the modified zeolite. The total concentration of acidic centers or the acidity
of Ga-HZSM-5 zeolite catalyst decreased with increasing silica to alumina ratio and
decreasing micro pore volume.

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