The role of carboxylic acid in cobalt Fischer-Tropsch synthesis catalyst deactivation

Oxygenated compounds have previously been detected on spent Co/Al2O3 FTS catalyst and have also been proposed to be precursors for carbon formation. Build-up of polymeric carbon on the catalyst during Fischer-Tropsch synthesis (FTS) can negatively influence activity over an extended reaction time. Adsorbed oxygenates detected on spent Cohi-Al2O3 FTS catalyst are deduced to be located on the gamma-Al2O3 support using attenuated total reflectance infrared spectroscopy (ATR-IR). The formation of a metal-carboxylate compound is not detected (ATR-IR) and deduced to be unlikely since acetic acid decomposes at low temperature on a Co metal surface (single crystal Co(0 0 01) experiments under ultra-high vacuum conditions). Acetic acid undergoes dissociative adsorption on the gamma-Al2O3 (1 10) and (1 0 0) surfaces (DFT), forming an acetate species. Acetic acid vapor, contacted with reduced Co/Pt/Al2O3 catalyst at model FTS conditions (i.e. 1 baro) H-2/CO:2/1 at 230 degrees C), results in predominantly atomic carbon deposition on the catalyst. Co-feeding of excess acetic acid during FTS does not enhance Co/Pt/Al2O3 catalyst deactivation nor does it significantly impact methane selectivity. Therefore, carboxylic acids can cause atomic carbon formation on Cohi-Al2O3 catalyst during FTS and result in strongly adsorbed carboxylates on gamma-Al2O3 support, but these factors do not significantly impact catalyst deactivation. (C) 2015 Elsevier B.V. All rights reserved.