A novel preparation method for small eggshell Co/-γ-Al2O3 catalysts: A promising catalytic system for compact Fischer-Tropsch reactors

Due to the need of limiting pressure drop, and the consequent necessity of adopting big catalyst pellets, low-temperature Fischer-Tropsch synthesis in industrial fixed-bed reactors may suffer of strong intra-particle mass transport limitations, which are known to result in decreased CO conversion rate and C-5(+) selectivity. Upon decoupling the pellet diameter and the diffusive length, eggshell catalysts represent an engineering solution for the intensification of the Fischer-Tropsch reactors. In this work, preparation, characterization and testing of impregnated Co/gamma-Al2O3 eggshell catalysts with sharply defined outer shell regions are reported. The method developed to impregnate the active phase only on the outer layer of the support is based on the protection of the inner pores of the support with an organic liquid and on the control of the contact time between the impregnating solution and the protected support. The method is particularly suitable to prepare small eggshell pellets, with diameters below 1 mm, to be used in compact FT reactors. It is shown that 600 mu m pellets, with catalytically active layers 75 mu m thick, grant a remarkable combination of high CO conversion rate and high C-5(+) selectivity, thus resulting extremely interesting for operations in reactors 3-6 m long. (C) 2014 Elsevier B.V. All rights reserved.