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, composed of ultrathin framework with possessing uniform-sized (~ 4 nm) mesopores. Interestingly, the mesopore size was systematically increased to 12 nm by increasing the amount of trimethylbenzene additive in the synthetic gel. Such a zeolite beta nanosponge with tailoring mesopore diameter was investigated as a support of Co catalyst for Fischer-Tropsch synthesis. By the confining effect of the mesopore, the size of Co nanoparticle was finely controlled, closely fitted to the mesopore size. Despite same content of Co catalyst, CO conversion was gradually increased with increasing the Co particle size, showing optimal point at 10 nm of the particle size. The selectivity of gasoline-ranged long-chain hydrocarbons increased also with similar trend over short hydrocarbons, attributed to higher chain growth probability in larger Co particles. Meanwhile, Co supported on zeolite beta nanosponge exhibited high selectivity for iso-paraffins, as compared to bulk zeolite counterpart and MFI nanosponge, attributed to shorter diffusion path lengths for branched hydrocarbons to avoid subsequent cracking and weaker acidity lowering the tendency of the cracking, respectively. Consequently, Co supported on zeolite beta nanosponge with 10 nm of mesopore size shows high yield of gasoline-ranged branched hydrocarbons.

Keywords: Fischer-Tropsch synthesis, Co supported on zeolite nanosponge, size effect, gasoline-range, branched-hydrocarbon