Effect of Reducing Agents (Syngas, H2 and CO) on the Catalytic Performance of Iron Catalysts for Fischer-Tropsch Synthesis

Reduction of the iron catalyst precursor is an important stage during Fischer-Tropsch (FT) reaction and reducing gases tend to influence the activity, selectivity and the catalyst life span. Hydrogen is mostly the used reducing gas in FT because of its ability to avoid the buildup of carbon during the FT synthesis (Jia et al. 2007). Reduction with carbon monoxide alone gives very active catalysts but may favor carbon deposition. Economic benefits can potentially be obtained if the same syngas used for the normal FT reaction can also be used to activate the catalyst at the normal FT reaction temperature. The current study focus on the investigation of the effect of reducing agents (syngas, H₂ and CO) on the catalytic performance of a precipitated iron based catalyst for Fischer-Tropsch synthesis (FTS). Three fixed bed reactors (FBR), each loaded with 1 gram of the same iron based catalyst, were set in parallel and simultaneously reduced  with syngas (CO/H₂ ), H₂ and CO, respectively,  for 48 hrs at 250 ^oC, at atmospheric pressure using  a flowrate of 60 (NTP)ml/min. After the reduction, the same FT reaction procedures were carried out among the three reactors for more than 1000 hrs. The experimental data demonstrated that the catalyst activities for FTS followed a decreasing order: syngas > hydrogen > carbon monoxide reduced. More experimental results, such as the FT reaction rates, water-gas-shift (WGS) reaction rates, product selectivity and the paraffin to olefin ratios are calculated and compared.  The study provides an indication that the reducing gas used has a long term effect on the catalyst activity and product selectivity.