Carbon coated cobalt catalysts for direct synthesis of middle n-alkanes from syngas.

Core-shell structure catalysts with adjustable carbon shell thickness and pore size were obtained by dissociating acetylene, leading to new product distribution characteristics: (1) the core–shell catalyst without reduction still showed high activity, and showed high selectivity of C 5 ∼C 12 (48.5%); (2) after reduction, it had the same activity as the uncoated catalyst, and showed high selectivity of C 13 ∼C 20 (41.7%), and high selectivity of C 5 ∼C 20 (66.9%); (3) more than 90% of the products are n-alkanes. [Display omitted] • Carbon coated catalysts were obtained at a low acetylene dissociation temperature. • The thickness of carbon coating can be regulated based on the dissociation temperature. • The carbon coating can determine the FTS products distribution. • More than 90% of the FTS products are n-alkanes. A series of carbon coated core–shell cobalt catalysts with different thickness of shell were easily prepared by C 2 H 2 dissociation. The characterization results showed that dissociation temperature plays an important role in determining the thickness of carbon shell. There were two kinds of carbon species on the surface of coated catalysts: deposited carbon and graphitic carbon. Only deposited carbon could be obtained during lower temperature coating, while both deposited carbon and graphitic carbon were found during higher temperature coating. Deposited carbon blocked the active sites, while graphitic carbon didn't block the active sites but only limited the diffusion of the products. The coated catalyst possessed better dispersion and reduction, and retains more elemental Co after surface passivation. The performance test results of Fischer-Tropsch synthesis (T = 220 °C) indicated that: (1) the core–shell catalyst without reduction still showed high activity, and showed high selectivity of C 5 ∼ C 12 (48.5%); (2) after reduction, it had the same activity as the uncoated catalyst, and showed high selectivity of C 13 ∼ C 20 (41.7%), and high selectivity of C 5 ∼ C 20 (66.9%); (3) more than 90% of the products were n-alkanes. [ABSTRACT FROM AUTHOR]