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Keywords:

  • Fischer–Tropsch synthesis;
  • molybdenum carbide;
  • temperature-programmed carburization;
  • Ba-promotion

Abstract

Background

Traditional FT catalysts such as Co and Fe still suffer from carbon-induced deactivation even with alkali promotion. The objective of this study was to examine the effect of Ba addition to carbon-tolerant Mo carbide since it has Pt-like characteristics and is cheaper than noble metals as an FT catalyst.

Results

The presence of Ba increased the Mo carbide production rate and reduced the activation energy for its formation. The promoted catalyst exhibited higher specific basic site strength and CO2 uptake for strong basic site than that of the undoped catalyst. Both catalysts exhibited optimal reaction rate at a H2 mole fraction of 0.75 while CO consumption rate, total olefin-to-paraffin ratio, methane suppression as well as C5+ selectivity were improved with Ba addition. The non-standard Anderson–Schulz–Flory (ASF) product distribution observed for the Ba-doped catalyst may be due to the appearance of an additional polymerization site on the catalyst surface located in the BaMoO4 phase. Chain growth factor was enhanced by up to 93% from 0.43 to 0.83 with the Ba-doped catalyst.

Conclusions

Ba promoter increased chain growth probability by about 93%. The deviation of product distribution from standard ASF plots with 2 chain growth factors for the 3wt%Ba-10%MoC1-x/Al2O3 catalyst was probably due to the presence of different active sites for chain initiation. The result is unprecedented and represents excellent opportunity for industrial exploitation of a new and relatively cheap carbon-resistant catalyst.© 2012 Society of Chemical Industry