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Water as key to activity and selectivity in Co Fischer-Tropsch synthesis: γ-alumina based structure-performance relationships

Abstract

Thirteen γ-alumina supports with different pore sizes and pore size distributions have been impregnated with cobalt and rhenium. The catalysts were tested for Fischer-Tropsch synthesis (FTS) under dry and enhanced water vapor pressure conditions. It is shown that there is a positive correlation between pore size and cobalt crystallite size of the reduced catalyst after incipient wetness impregnation as long as the pore size distribution is sufficiently narrow. There is a concurrent increase in C5+ with pore diameter due to higher chain propagation probabilities α3+. Higher α values are ascribed to larger cobalt crystallites that promote CO activation resulting in higher surface coverage of CHx monomers. Adding water vapor to the syngas feed has a strong positive effect on selectivity to higher hydrocarbons and activity. Water imposes a significant enhancement of α1 that is attributed to higher relative cobalt surface coverage of H2O(OH−) and CHx relative to hydrogen. Small pores are susceptible to condensation of water during FTS.
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Category

Academic article

Language

English

Author(s)

Affiliation

  • SINTEF Industry
  • Norwegian University of Science and Technology

Year

2018

Published in

Journal of Catalysis

ISSN

0021-9517

Volume

365

Page(s)

334 - 343

View this publication at Norwegian Research Information Repository