Production of C-4 hydrocarbons from modified Fischer-Tropsch synthesis over Co-Ni-ZrO2/sulfated-ZrO2 hybrid catalysts

Fischer-Tropsch synthesis was carried out at atmospheric pressure in a fixe d-bed microreactor at temperatures and weight hourly space velocities (WHSV ) ranging from 513 to 533 K and 5 to 25 h(-1), respectively, over hybrid ca talysts (physical mixtures) containing Co-Ni-ZrO2 and sulfated-ZrO2 catalys ts. The sulfated-ZrO2/Co-Ni-ZrO2 catalyst weight ratios (SZ/CN) ranged from 0 to 3, whereas sulfate concentrations in sulfated-ZrO2 catalyst (sulfate loading) ranged from 5 to 15 wt %. Fischer-Tropsch synthesis over Co-Ni-ZrO 2 catalyst alone produced a maximum C-4 hydrocarbon selectivity of 14.6 wt % at a temperature of 523 K and WHSV of 15 h(-1). There was an impressive i ncrease in C-4 hydrocarbons selectivity to a maximum of 32.4 wt % when cata lyst HB5,1 (SZ/CN of 1 and sulfate loading of 5 wt %) was used. This cataly st also gave an extremely high selectivity for isobutane (maximum of 10.6 w t % of total hydrocarbon products) as compared to 0.1 wt % obtained with Co -Ni-ZrO2 catalyst. A time-on-stream study on catalyst HB5,1 showed a decrea se in activity of this catalyst with reaction time. In contrast, the use of hybrid catalyst HB5,0.5 (SZ/CN of 0.5 and sulfur loading of 5) where the o verall sulfur content was low resulted in almost no deactivation. However, the activity obtained in the case of catalyst HB5,0.5 was lower than that o btained for catalyst HB5,1 but was much higher than that for Co-Ni-ZrO2 cat alyst. On the other hand, for hybrid catalysts HB5,2 and HB15,1, which had high overall concentrations of sulfur, there was no activity at all. The re sults show that interactions brought about by close proximity of Fischer-Tr opsch catalyst active sites and acid sites produce favorable effects when t he overall sulfur content in the hybrid catalyst is low.