Mesoporous Beta Zeolite-Supported Ruthenium Nanoparticles for Selective Conversion of Synthesis Gas to C5-C11 Isoparaffins

Mesoporous beta (meso-beta) zeolites prepared by post-treatment of H-beta with NaOH aqueous solution were studied as supports of Ru catalysts for Fischer-Tropsch (FT) synthesis. The size and volume of the mesopores increased with the concentration of NaOH. The Bronsted acidity declined because Na+ ions were exchanged into the meso-beta during the post-treatment, and a further ion exchange of the meso-beta with NH4+ followed by calcination, forming H-meso-beta, could recover the Bronsted acidity. The use of H-meso-beta or meso-beta instead of H-beta or Na-beta as the support for FT synthesis decreased the selectivities to CH4 and heavier hydrocarbons (C-12(+)) and increased that to C-5-C-11 hydrocarbons. The C-5-C-11, selectivity depended on the concentration of NaOH used for meso-beta preparation. Under an optimum NaOH concentration, a C-5-C-11 selectivity of 77%, significantly higher than the maximum expected from Anderson-Schulz-Flory distribution (similar to 45%), was attained with a ratio of isoparaffins to n-paraffins being 2.7. The mesoporosity and the unique acidity of the meso-beta probably contribute to the selective hydrocracking of the primary heavier hydrocarbons formed on Ru nanopartides into gasoline-range liquid fuels.