(440b) Deactivation Behavior of MWCNTs and Activated Carbon-Supported Alkali-Promoted Trimetallic Co-Rh-Mo Sulfide Catalysts for Higher Alcohols Synthesis From Synthesis Gas

Alkali-modified Co-Rh-Mo trimetallic catalysts supported on multi-walled carbon nanotubes (MWCNTs) and activated carbon were used to study the long term deactivation for continuous 720 h of higher alcohols synthesis from synthesis gas. The deactivation behavior of the catalysts were tested for the synthesis of higher alcohols from synthesis gas under similar conditions of 330°C, 9.1 MPa (1320 psig), and 3.8 m³ (STP)/(kg of cat.)/h using H₂ to CO molar ratio of 1.25. The catalysts were extensively characterized in both oxide and sulfide phases before reaction, together with the spent catalysts. The alkali-promoted trimetallic Co-Rh-Mo catalyst supported on MWCNTs has shown two different deactivation steps: loss of sulfur from the surface and sintering of the catalyst species located on the outer surfaces of the carbon nanotubes. After regeneration, the total activity recovery (about 10%) is close to the total activity loss during the first deactivation step over this catalyst. The % CO conversion decreased from 58% and 43 % to 51% and 30% over the catalysts supported on MWCNTs and activated carbon, respectively. Characterizations of the spent catalyst supported on activated carbon revealed that deactivation occurs due to sintering of metal sulfides, which causes low metal dispersions and high pore blockage of the support.