A simple
method was developed and tested to synthesize hierarchical
ZSM-5 zeolites using tetrapropylammonium hydroxide as a sole structure
directing agent to generate intercrystalline mesopores. XRD analysis
confirmed the formation of ZSM-5 zeolites. SEM and TEM imaging analyses
revealed the presence of hierarchical structure, formed by self-assembly
of highly crystalline, nanosized primary particles. Solid-state MAS
NMR analysis showed the vast majority of Al atoms were tetrahedrally
incorporated with Si atoms in the zeolite framework. N2 physisorption studies indicated that the mesopores of an average
pore size of 30 nm were created in the hierarchical ZSM-5 zeolites
with an abundance of micropores. The performance of these zeolites
in catalyzing methanol to gasoline conversion was evaluated using
a fixed-bed reactor operating at 350 °C with ca. 16.5% methanol
in nitrogen at a total pressure of 1.1 MPa and WHSV of 1.2 h–1. The hierarchical ZSM-5 zeolites exhibited almost 100% methanol
conversion and 59% selectivity toward the gasoline range hydrocarbons.
The coke formation on the used catalyst was studied using a N2 physisorption technique and a thermogravimetric analyzer.
The hierarchical ZSM-5 zeolite showed less than 2% coke formation
and deposition over 24 h on stream, much less compared to the conventional
ZSM-5 zeolite with nearly 8% carbon deposition under the same reaction
conditions.
Highlights Nanocrystal ZSM-5 of different SiO2/Al2O3 ratios but same sizes were obtained The effect of SiO2/Al2O3 ratio on methanol to gasoline was systematically studied Increasing SiO2/Al2O3 ratio reduced durene yield and improved catalyst durability Low SiO2/Al2O3 ratios promoted C1-C4 and durene selectivity Catalysts with low SiO2/Al2O3 ratios deactivated more rapidly due to coking
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