Zeolite beta nanosponge supporting uniform sized cobalt nanoparticles, exhibiting high yield of branched hydrocarbons in gasoline range in Fischer-Tropsch synthesis

Abstract

We synthesized zeolite beta nanosponge using a zeolite-structure-directing surfactant, resulting in an ultrathin framework with uniform-sized (∼4 nm) mesopores. Notably, the mesopore size was systematically increased to 12 nm by adjusting the amount of trimethylbenzene additive in the synthetic gel. Such a zeolite beta nanosponge with tailoring mesopore diameter was investigated as a support for Co catalyst in Fischer–Tropsch synthesis. Owing to the confinement effect of the mesopores, the size of the Co nanoparticles was precisely controlled to match the mesopore dimensions. Despite the same Co content, CO conversion gradually increased with larger Co particle sizes, reaching an optimal performance at a particle size of 10 nm. A similar trend was observed in the selectivity for gasoline-range hydrocarbons, attributed to the higher chain growth probability associated with larger Co particles. Meanwhile, Co supported on the zeolite beta nanosponge exhibited significantly higher selectivity for iso-paraffins compared to its bulk zeolite and MFI nanosponge counterparts. This enhancement was attributed to the shorter diffusion path, which allowed branched hydrocarbon intermediates to avoid excessive cracking, and the weaker acidity, which reduced the tendency for secondary cracking. Consequently, the Co-supported zeolite beta nanosponge with a 10 nm mesopore size achieved a high yield of branched hydrocarbons in gasoline range.