Correlation between Hydrocarbon Product Distribution and Solvent Composition in the Fischer–Tropsch Synthesis Catalyzed by Colloidal Cobalt Nanoparticles

Abstract

Colloidal cobalt nanoparticles with well-defined particle size (ca. 2.7 nm) were synthesized, characterized, and tested in Fischer−Tropsch synthesis (FTS) using water and binary mixtures as solvent. The catalytic results revealed that activity and selectivity strongly depend on the nature and composition of the solvent mixture: the tests in pure water produced light hydrocarbons (C 2 − C 4 ), while the addition of organic cosolvents increased the activity and shifted the selectivity to higher hydrocarbons (C 13 −C 30 ). The observed variations in the activity and selectivity were correlated to syngas solubility in the medium used for catalysis. Under the tested conditions, ethanol/water (93/7 v/v) appeared to be the optimum binary solvent in terms of FT activity.

Effect of the Polymeric Stabilizer in the Aqueous Phase Fischer-Tropsch Synthesis Catalyzed by Colloidal Cobalt Nanocatalysts

“…45°, 35°, and 60° ( Figure 3 ). The broadening of XRD peaks was previously observed for CoNPs prepared by chemical reduction using NaBH 4 [ 23 , 24 ], and associated to the small size and/or to the amorphous structure of the NPs [ 25 , 26 ]. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed the presence of Na, Co, O, N, C, and B. Deconvolution of the Co 2p XPS spectra (see Supporting Information) revealed that the metallic cobalt content ranged from 6% to 67% for this series of NPs.…”

“…This particular product distribution is attributed to mass transfer limitations when water is used as the reaction solvent due to the relatively low solubilities of CO and H 2 in water [23]. From the series of tested catalysts, Co2 and Co5 exhibited the lowest and the highest α values (0.50 vs. 0.66, respectively).…”

“…0.10 mol CO mol Suf- Co −1 h −1 (at 170 °C under 30 bar of syngas in water) for PVP stabilized CoNPs [ 10 , 16 ]. Other studies in which different reaction solvents were employed in FTS are difficult to compare to our aqueous system due to the dependence on mass transfer and syngas solubility as a function of the reaction solvent [ 23 ].…”

“…It is noteworthy that under the current conditions using water as the solvent, the chain length of the hydrocarbon products was not longer than C 9 (See ASF Distributions in Supporting Information). This particular product distribution is attributed to mass transfer limitations when water is used as the reaction solvent due to the relatively low solubilities of CO and H 2 in water [ 23 ]. From the series of tested catalysts, Co2 and Co5 exhibited the lowest and the highest α values (0.50 vs. 0.66, respectively).…”

Effect of pH on catalyst activity and selectivity in the aqueous Fischer–Tropsch synthesis catalyzed by cobalt nanoparticles

“…Very recently, our group reported the effect of the addition of organic co-solvents in the Aqueous phase Fischer-Tropsch Synthesis and it was concluded that the catalysis in water is strongly limited due to the extremely low syngas solubility in this solvent. [24] Regarding the product distribution, the increase of the pH from 7 to 13.3 resulted in the slight decrease of the alpha value from 0.59 to 0.52. This observation agrees with the increase of H 2 :CO ratio during the reaction under basic conditions, resulting in the increase of the chain termination rate and the production of shorter hydrocarbons.…”