Iso-paraffins synthesis from modified Fischer-Tropsch reaction-Insights into Pd/beta and Pt/beta catalysts

The direct iso-paraffin synthesis from synthesis gas (CO + H2, syngas) via Fischer-Tropsch (FT) route was investigated in a consecutive dual reactor system, in which FT reaction was carried out over Co/SiO2 catalyst in the upper reactor and hydroconversion of the FT hydrocarbons occurred over Pt/beta or Pd/beta catalyst in the lower reactor. The products with very high iso-paraffin selectivity were composed mainly of hydrocarbons with carbon number less than 10, indicating that both hydrocracking and hydroisomerization reactions significantly occurred. Under the present operating conditions, time-on-steam results indicate that Pt/beta catalyst containing 0.5 wt.% Pt deactivated quickly while 0.5 wt.% Pd/beta catalyst showed stable performance in the case of iso-paraffin selectivity. Either the increase in Pt loading to 1 wt.% Pt or the increase of hydrogen partial pressure in the lower reactor can alleviate the deactivation of the catalyst for the titled reaction. This was mainly ascribed to the different effect of the adsorbed CO molecule on the metallic function of Pt and Pd.