Direct Synthesis of Hierarchical ZSM-5 Zeolite and Its Performance in Catalyzing Methanol to Gasoline Conversion

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. N 2 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 N 2 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.