The effects of ionic additives on the aqueous-phase Fischer–Tropsch synthesis with a ruthenium nanoparticle catalyst

Abstract

The effects of ionic additives on the catalytic activity and product distribution of hydrocarbons and oxygenates were studied on the reaction of quasi-homogeneous ruthenium nanoparticle (Ru NP) catalyst for aqueous phase Fischer–Tropsch synthesis (AFTS). A variety of potassium and sodium salts, as well as KOH and NaOH were used as the ionic additives in the AFTS reactions either after the synthesis of Ru NPs (R1) or during the synthesis of Ru NPs (R2, which was used directly in the following AFTS process). The additions of Cl−, OH−, HCO3−, H2PO4−, and CO32− through R2 way enhanced the AFTS activity, while the addition of F− in R2 way led to a significant deactivation for Ru NPs catalyst. For the selectivities of products, potassium and sodium additives increased the selectivity of C5–C12 hydrocarbons, and suppressed formation of olefins and oxygenates. F− decreased the content of C13+ hydrocarbons and shifted selectivities towards lower-molecular-weight hydrocarbons (C1–C4). The additions of Br− (added in R2 way) and I− dramatically increased the content of alcohols in oxygenate products. In all cases, ASF distribution of hydrocarbons (C1–C29) and analogous ASF distribution of oxygenates (aldehydes from C9 up to C27) were obtained. The addition of I−, PO43−, H2PO4− and Br− in R2 way resulted in the aggregation of Ru NPs. However, the catalysts with these additives still maintained remarkable activities. Moreover, the particle size and morphology of Ru NPs in other cases showed little correlation with the participation of ionic additives, demonstrating that they were more in the line of electronic promoter instead of structural directing agent for Ru NPs. The proposed mechanism was verified by the CO adsorption experiments.