Effect of H2S in Syngas on the Fischer–Tropsch Synthesis Performance of a 0.5%Pt–25%Co–Al2O3 Catalyst

• Published in: Catalysis letters 2016-07, Vol.146 (7), p.1204-1212
• Main Authors: Ma, Wenping, Jacobs, Gary, Shafer, Wilson D., Pendyala, Venkat Ramana Rao, Xiao, Qunfeng, Hu, Yongfeng, Davis, Burtron H.
• Format: Article
• Language: English
• Subjects: Alkenes; Aluminum oxide; Catalysis; Catalysts; Chemistry; Chemistry and Materials Science; Cobalt; Deactivation; Fischer-Tropsch process; Gas mixtures; Hydrocarbons; Hydrogen sulfide; Industrial Chemistry/Chemical Engineering; Organometallic Chemistry; Physical Chemistry; Platinum; Selectivity; Slurries; Sulfidization; Sulfur; Synthesis gas; Unsteady state
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-016-1747-0

The effect of 1.0 ppm H 2 S in the syngas feed on initial activity and selectivity of a 0.5%Pt–25%Co/Al 2 O 3 catalyst was studied by comparing the catalyst performance under H 2 S and sulfur free conditions. The reaction tests were performed using a 1-L slurry phase reactor for 141–212 h under constant reaction conditions: 220 °C, 2.0 MPa, H 2 /CO = 2.0 and 6.0 Nl/g-cat/h. In the H 2 S poisoning test, an H 2 S in N 2 gas mixture was added to the syngas feed (1.0 ppm) after running the Fischer–Tropsch synthesis (FTS) reaction for ca. 6.0 h; as such, the impact of H 2 S on the initial deactivation of the cobalt catalyst (unsteady state) was successfully assessed. The used catalysts were characterized by XANES to investigate if Co–S surface species were formed during the deactivation. The initial deactivation under 1.0 ppm H 2 S condition was significantly higher (by 2.0–2.4 times) than that under clean conditions. CH 4 selectivity increased substantially and C 5+ selectivity decreased greatly with time regardless of whether H 2 S was added or not; however, the addition of H 2 S accelerated the changes in the hydrocarbon selectivities, which were likely caused by the sharp deactivation of the catalyst in the presence of H 2 S. After co-feeding the sulfur for 141 h, a comparison was made at similar conversions by adjusting space velocity; the sulfur pretreated cobalt catalysts favored heavier hydrocarbons (C 5+ ) formation and suppressed lower hydrocarbon formation. The addition of H 2 S to the feed increased CO 2 selectivity and the secondary reaction of 1-olefins. The XANES results revealed that surface species involving Co–S bonding formed on the cobalt catalyst after exposure to H 2 S during FTS. This was likely the primary reason for the abnormal selectivity trends observed during and after the deactivation of the catalyst by sulfur. This study points out a possible approach to increase the selectivity to heavy hydrocarbons by properly sulfiding the cobalt catalyst prior to the FTS reaction. Graphical Abstract