Further insights into methane and higher hydrocarbons formation over cobalt-based catalysts with gamma-Al2O3, alpha-Al2O3 and TiO2 as support materials

摘要

A range of cobalt-based catalysts varying in Co loading and prepared by incipient wetness impregnation of traditional support materials (gamma-Al2O3, alpha-Al2O3 and TiO2), have been studied in the Fischer-Tropsch reaction at industrially relevant process conditions (483 K 20 bar, H-2/CO = 2.1). A high selectivity to C5+ hydrocarbons (SC5+) is to a great extent connected with a high site activity, but not exclusively. We propose that the ratio of monomer-production rate to C-C coupling rate of a catalyst determines chain growth probability by means of governing the coverage of the monomer on the cobalt surface. We speculate that this ratio depends on e.g. shape, strain and size of the Co crystallites and, therefore, is highly dependent on the choice of support material. No general relationship between Co particle size and SC5+ is found, but individual correlations exist for each support material.