Fischer-Tropsch Synthesis: Influence of Acid Treatment and Preparation Method on Carbon Nanotube Supported Ruthenium Catalysts

The influences of nitric acid treatment on a carbon nanotube (CNT) support and the preparation method, incipient wetness impregnation (IWI) versus chemical vapor deposition (CVD), on catalytic performance during Fischer Tropsch (FT) synthesis were examined using a slurry phase reactor. Acid treated CNT (ACNT) supported Ru catalysts exhibited higher activities compared to Ru supported on untreated CNTs (UCNTs). The acid-treated CVD catalyst had higher initial CO conversion (smaller average Ru particle size) but sintered more due to a greater tendency for Ru to be deposited exterior to CNT channels relative to IWI. After the initial decline andleveling off period, the ACNT IWI catalyst had the highest steady activity among the catalysts tested. The ACNT IWI catalyst also displayed greater oxygenate selectivity (similar to 17%) compared to ACNT CVD (similar to 12%) and UCNT IWI similar to 10%) catalysts at similar conversions. Acid treatment created adsorption sites on the CNT surface that anchor Ru precursors and promote CO insertion and/or OH addition leading to alcohols. Acid treatment also opened end-caps and broke tubes at defects, resulting in shorter diffusional path-lengths, and allowing Ru to be deposited within CNT channels (especially for IWI).