ORALS

SESSION: PhysicalSatAM-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Sat Oct, 26 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Michael Stoukides; Costas Galiotis; Session Monitor: TBA

12:35: [PhysicalSatAM04]
Consequences of Important Parameters on the Effect of Water on Fischer-Tropsch Synthesis Rate and Selectivity
Klito C. Petallidou¹ ; Enrique Iglesia² ; Angelos Efstathiou³ ; ¹University of California at Berkeley, University of Cyprus, Nicosia, Cyprus; ²University of California at Berkeley, Berkeley, United States; ³University of Cyprus, Nicosia, Cyprus;
Paper Id: 195 [Abstract]

Water is one of the main products of Fischer-Tropsch (FT) synthesis and its effect on the FT rate has been reported to be positive [1], negative [2], or negligible [1]. The void structure plays an important role on the effect of water on the FT rate [1]. Catalysts with large void structures show positive effects of water on the turnover rate, while catalysts with small void structure show negligible effects. In the case of small void structures, the condense H₂O phase may already exist, while large void structures, require higher water pressure for intrapore condensation [1, 3]. Also, it has been reported that these enhancement rates with increasing water pressure are due to stabilization of kinetically-relevant step through H-transfer [4]. Kinetic and spectroscopic experiments were used to address the influence of the void structure on the effect of water on the rate and selectivity of FT synthesis over Cobalt-based catalysts and the consequences of (i) Cobalt particle size, (ii) extent of reduction of Cobalt, (iii) total pressure of CO/H₂ and (iv) reaction temperature. The consequences of these important parameters on the influence of void structure on the effect water remain unanswered until now. The present study provides a useful and important contribution to the state-of-the-art important kinetic and mechanistic aspects of FT synthesis. These rate enhancements caused by water are independent of the particle size and the extent of reduction of cobalt. Water plays an important role on the reaction temperature and the total pressure of reactants. Catalysts with large void structures show positive effects of water on the turnover rate at lower reaction temperatures and higher pressures, while at higher reaction temperatures and lower pressures minor effects are observed. Catalysts with small void structure show negligible effects of water on the rate in all experimental conditions. In all cases (small and large void structure), CH₄ selectivity decreases and C₅⁺ selectivity increases with increasing the water partial pressure, except at higher temperatures and lower pressures, where the selectivities are constant. These results reinforce the previous proposal for intrapore condensation of liquid water.

References:
[1] E. Iglesia, Appl. Catal. A: Gen. 161 (1997) 59-78.
[2] A.M. Hilmen, D. Schanke, K.F. Hanssen, A. Holmen, Appl. Catal. A: Gen. 186 (1999) 169-188.
[3] S. Krishnamoorthy, M. Tu, M.P. Ojeda, D. Pinna, E. Iglesia, J. Catal. 211 (2002) 422-433.
[4] D.D. Hibbitts, B.T. Loveless, M. Neurock, E. Iglesia, Angew. Chem. Int. Ed. 20 (2013) 12273-12278.