Fischer–Tropsch synthesis: Effect of ammonia on supported cobalt catalysts

Fischer-Tropsch Synthesis for the Production of Sustainable Aviation Fuel: Formation of Tertiary Amines from Ammonia Contaminants

Fischer-Tropsch synthesis combined with product workup is a promising route toward synthetic aviation fuel from renewable hydrogen and carbon sources like biomass, CO2, and waste. Cost savings can be achieved by reducing the number of gas treatment steps in new plants, but the consequence of contaminants in the feed needs investigation. While feeding 2.6 ppmV ammonia to a Fischer-Tropsch reactor, it was shown that ammonia was predominantly chemically converted into organic amines, with most nitrogen found in the water phase (89%), followed by heavy wax (7%) and light wax (1%). The concentration difference between water and light wax was shown to be due to the post-condensation separation of amines on polarity. Amines up to a chain length of 120 were detected in the heavy wax with MALDI-FT-ICR-MS, which, in combination with the high nitrogen content, suggests that amines have a similar chain growth probability compared to the main hydrocarbon products. Detailed product analysis with three independent analytical techniques showed that tertiary N,N-dimethylalkylamines were by far the most abundant amine class. This suggests that ammonia is decomposed on the cobalt surface and, potentially as a dimethylamine fragment, incorporated in the growing chain. Further evidence was obtained from the abundance of trimethylamine and from the reconciled nitrogen product analysis up to C100, which showed that the amine product distribution followed from naphtha onward the same ASF kinetics as alkanes and oxygenates while being distinctively different from the alkene distribution. The presented findings provide further avenues for studies of the Fischer-Tropsch reaction mechanism and indicate the opportunity of cost saving on gas treatment, while further validation is required to assess the impact on hydrocracking and product quality.

Growth, sintering, and chemical states of Co supported on reducible CeO2(111) thin films: The effects of the metal coverage and the nature of the support

The growth, sintering, and interaction of cobalt with ceria were studied under ultrahigh vacuum conditions by vapor-deposition of Co onto well-defined CeO_x(111) (1.5 < x < 2) thin films grown on Ru(0001). Charge transfer from Co to ceria occurs upon deposition of Co on CeO_1.96 and partially reduced CeO_1.83 at 300 K. X-ray photoelectron spectroscopy studies show that Co is oxidized to Co²⁺ species at the cost of the reduction of Ce⁴⁺ to Ce³⁺, at a lesser extent on reduced ceria. Co²⁺ is the predominant species on CeO_1.96 at low Co coverages (e.g., ≤0.20 ML). The ratio of metallic Co/Co²⁺ increases with the increase in the Co coverage. However, both metallic Co and Co²⁺ species are present on CeO_1.83 even at low Co coverages with metallic Co as the major species. Scanning tunneling microscopy results demonstrate that Co tends to wet the CeO_1.96 surface at very low Co coverages at room temperature forming one-atomic layer high structures of Co-O-Ce. The increase in the Co coverage can cause the particle growth into three-dimensional structures. The formation of slightly flatter Co particles was observed on reduced CeO_1.83. In comparison with other transition metals including Ni, Rh, Pt, and Au, our studies demonstrate that Co on ceria exhibits a smaller particle size and higher thermal stability, likely arising from strong metal-support interactions. The formed particles upon Co deposition at 300 K are present on the ceria surface after heating to 1000 K. The Co-ceria interface can be tuned by varying the Co metal coverage, the annealing temperature, and the nature of the ceria surface.

Effect of ammonia on cobalt Fischer–Tropsch synthesis catalysts: a surface science approach

Undercoordinated (defect) sites on cobalt surfaces favor NH₃ decomposition and dehydrogenated products adsorb strongly around these defect sites.

Biochemicals from food waste and recalcitrant biomass via syngas fermentation: A review

An effective method for the production of value-added chemicals from food waste and lignocellulosic materials is a hybrid thermal-biological process, which involves gasification of the solid materials to syngas (primarily CO and H₂) followed by fermentation. This paper reviews the recent advances in this process. The special focus is on the cultivation methods that involve the use of single strains, defined mixed cultures and undefined mixed cultures for production of carboxylic acids and higher alcohols. A rate limiting step in these processes is the low mass transfer between the gas and the liquid phases. Therefore, novel techniques that can enhance the gas-liquid mass transfer including membrane- and trickle-bed bioreactors were discussed. Such bioreactors have shown promising results in increasing the volumetric mass transfer coefficient (k_La). High gas pressure also influences the mass transfer in certain batch processes, although the presence of impurities in the gas would impede the process.

Fischer–Tropsch synthesis: effect of ammonia on product selectivities for a Pt promoted Co/alumina catalyst

The effects of co-fed ammonia in synthesis gas on the activity and product selectivities of a typical cobalt catalyst (0.5% Pt–25% Co/Al₂O₃) were investigated during the Fischer–Tropsch synthesis using a continuously stirred tank reactor (CSTR).