Transient HCO/HCOO species formation during Fischer-Tropsch over an Fe-Co spinel using low Ribblet ratio syngas: a combined IR and kinetic study

• Published in: Sustainable energy & fuels Vol. 7; no. 3; pp. 78 - 726
• Main Authors: Bahri, Shashank, Pathak, Shailesh, Upadhyayula, Sreedevi
• Format: Journal Article
• Published: 31.01.2023
• ISSN: 2398-4902
• DOI: 10.1039/d2se01282k

The comprehensive kinetics of simultaneous CO consumption in a Fischer-Tropsch and water-gas shift reaction network was systematically investigated over a supported FeCo 2 O 4 spinel catalyst. An operando FTIR-MS study reveals hydrogen-assisted cleavage of the C-O bond through intermediate formyl (HCO) species formation over the spinel catalyst surface as the prominent route for hydrocarbon chain initiation in the Fischer-Tropsch process. In accordance, the Langmuir-Hinshelwood-Hougen-Watson model confirms that the first reaction of adsorbed hydrogen (CO* + H* HCO* + *) is governed by equilibrium, while its second reaction (HCO* + H* C* + H 2 O*) is kinetically controlled. Six reaction mechanisms comprising Fischer-Tropsch and water-gas shift rate expressions were developed. These models were initially discriminated based on their accuracy to fit the random experimental data collected using a laboratory scale high pressure plug flow reactor with negligible heat and mass transfer limitations, and realistic kinetic parameters were estimated using the Levenberg-Marquardt algorithm. The relatively lower percentage of deviation in the comprehensive model than in other literature-reported models ensures the preciseness of the predicted data. Our mechanistic model FT-III3/WGS-I postulates that the atomic hydrogen-assisted decomposition of surface intermediate HCO initiates the hydrocarbon chain on Fischer-Tropsch active sites, whereas in water-gas shift active sites, the reaction between adsorbed CO and associative H 2 O to form intermediate formate (HCOO*) species controls water-gas shift activity when syngas of a low Ribblet ratio is used as a feedstock under conventional Fischer-Tropsch process conditions. The comprehensive kinetics of simultaneous CO consumption in a Fischer-Tropsch and water-gas shift reaction network was systematically investigated over a supported FeCo 2 O 4 spinel catalyst.