ORALS

SESSION: PhysicalThuPM1-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Thu Oct, 24 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Angelos Efstathiou; Alexandros Katsaounis; Session Monitor: TBA

14:25: [PhysicalThuPM106] Keynote
How Transient and Isotopic Techniques Advance the Design of Catalytic Materials for Industrial Dry Reforming of Methane to Syngas
Angelos Efstathiou¹ ; Michalis Vasiliades¹ ; Constantinos Damaskinos¹ ; ¹University of Cyprus, Nicosia, Cyprus;
Paper Id: 162 [Abstract]

During the last decades, several natural gas (NG) reservoirs were found to be rich in CO₂ (> 40 vol%), and this led to an intense effort for the development of a dry reforming of methane (DRM) catalytic technology (CH₄ + CO₂ to 2 CO + 2 H₂) with a favorable H₂/CO gas ratio for liquid fuels (Gas To Liquid, GTL) and other useful chemicals (e.g., DME, MeOH, acetic acid) by the catalysis research community and related industries [1]. Biogas (a renewable energy source) can also be a suitable feedstock for the DRM catalytic technology [2]. Practical problems related to the irreversible coking phenomena, especially on the less-costly attractive Ni-based catalysts, remain one of the main obstacles for the catalytic DRM technology to find industrial applications. It is well known that an in-depth understanding of the elementary steps related to carbon deposition and removal chemistry on Ni or other relevant metal supported catalytic systems along with their micro-kinetic analysis is a key factor for the future development of highly active and <br />carbon - resistant DRM catalytic systems, preferably at temperatures lower than 750 ^oC. This keynote lecture will present the use of various transient and isotopic experiments (use of ¹⁸O₂, ¹³CO₂ and ¹³CH₄) to elucidate the role of metal cation dopant in Ce_1-xM_xO₂ (M = Ti⁴⁺, Pr³⁺) used as support of Ni, and the use of Pt in the NiPt alloy supported on Ce_0.8Pr_0.2O₂, in reducing the carbon accumulation to a remarkable extent during DRM at 750^oC. In particular, the importance of carbon gasification by labile oxygen of support to the formation of CO(g), the contribution of oxygen vacant sites of support to the CO₂ dissociation rate and re-oxidation of support, and the quantification of the origin of carbon accumulation (CH₄ vs CO₂ activation route) will be elucidated [3, 4]. Other experimental approaches reported in the literature for the understanding of carbon deposition and removal chemistry on supported Ni and other metals will be presented. Experimental results from the SSITKA technique (use of ¹³CO₂ or ¹³CH₄) will be presented to demonstrate the effect of metal dopant on support and Pt on the active carbon that is strictly associated with the rate of reaction.

References:
[1] S. Afzal, D. Sengupta, A. Sarkar, M. El-Halwagi, N. Elbashir, ACS Sustainable Chem. Eng. 6 (2018) 7532-7544.\n[2] Ch. Papadopoulou, H. Matralis, X. Verykios, in:, L. Guczi, A. Erdohelyi (Eds.), Catal. Altern. Energy Gener., Springer New York, New York, NY, 2012, pp. 57-127.\n[3] C.M. Damaskinos, M.A. Vasiliades, A.M. Efstathiou, Appl. Catal. A: Gen., in press (doi.org/10.1016/j.apcata.2019.04.023).\n[4] M.A. Vasiliades, C.M. Damaskinos, K.K. Kyprianou, M. Kollia, A.M. Efstathiou, Catal. Today, in press (doi.org/10.1016/j.cattod.2019.04.022).

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.