Classifying and understanding the role of carbon deposits on cobalt catalyst for Fischer-Tropsch synthesis

Abstract

There is less agreement on the role of carbon deposits during FT reaction. Identifying and characterizing carbon species of cobalt catalyst is highly challenging for the Fischer-Tropsch Synthesis (FTS). Here, a serial of predeposited composite carbon and single carbon are constructed, and their roles in F-T synthesis are investigated on metal cobalt catalyst excluding the texture influence of the promoter and the support. Different carbon deposits are introduced on cobalt-based catalysts under different carbon-containing reducing atmospheres utilizing the pretreatment method. Atomic carbon, polymeric carbon, graphitic carbon, and combinations of them were distinguished by the characterization techniques of TPH, Raman and XPS. A significant difference occurred in both the catalytic activity and selectivity to methane after predeposited carbon on the Co-based catalysts. The p-Co-5 % syn-3 g-24 h-250-RO catalyst with single atomic carbon shows a remarkably low methane selectivity (4.03 %), high C5+ selectivity (76.38 %), and more importantly, excellent stability (TOS = 144 h) in FTS. Moreover, all of the Co-based catalysts containing the predeposited carbon can be directly used in the FT reaction without reduction procedure.