Dry-Gel MOR-to-MFI Interzeolite Transformation: Toward the Formation of the MTH Catalyst with a High Content of Paired Sites and Improved MTH Properties

A novel method of zeolite MFI synthesis with a controlled number of paired Al sites has been developed based on dry-gel interzeolite transformation (DG IZT) of the MOR zeolite. The composition of the dry gel, namely, the ratios of H2O/SiO2, NaOH/SiO2, and TPAOH/SiO2, was optimized to increase the number of paired sites in MFI zeolite up to 80%. In addition, it has been shown that the expensive TPAOH template commonly used for MFI zeolite synthesis can be replaced with a cheaper dipropylamine, yielding MFI zeolites with similar properties. The evaluation of the MOR-to-MFI catalysts obtained by the DG IZT method in the methanol-to-hydrocarbons (MTH) process suggests that the increase of paired sites share allows for improved catalyst stability with time on stream and higher propylene selectivity due to the enhanced contribution of the alkene cycle provided by paired sites.