ORALS

SESSION: PhysicalThuPM2-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: Vasileios Kyriakou; Dimitrios Zagoraios; Session Monitor: TBA

17:10: [PhysicalThuPM212]
Electrochemical Promotion of Methane Oxidation over Nanodispersed Pd/Co3O4 Catalysts
Dimitrios Zagoraios¹ ; Dimitrios Zagoraios² ; Alexandros Katsaounis³ ; Angel Caravaca⁴ ; Ioanna Kalaitzidou⁴ ; Athanasia Athanasiadi⁵ ; Spyros Ntais⁴ ; Philippe Vernoux⁶ ; Constantinos Vayenas² ; ¹University of Patras, Dept. of Chemical Engineering, Patras, Greece; ²University of Patras, Patras, Greece; ³Department of Chemical Engineering, University of Patras, Patras, Greece; ⁴University of Lyon, Lyon, France; ⁵University of Patras Dept. of Chemical Enginnering, Patras, Achaia, Greece; ⁶University LYON 1, Lyon, France;
Paper Id: 59 [Abstract]

During the last two decades, the Electrochemical Promotion of Catalysis (EPOC) phenomenon has been studied extensively for many catalytic reactions, including hydrocarbon oxidation reactions and hydrogenations [1-3]. The EPOC effect is based on the modification of the work function of a metal, which also serves as a working electrode, leading to an alteration in the chemisorption bond strength of the reactants. This effect is observed when small currents or potentials are applied to a catalyst deposited on a solid electrolyte. In the majority of the studies, the catalysts/electrodes consisted of porous noble metal films (Pt, Pd, Rh) prepared, for instance, by calcination of organometallic pastes [4]. This results in low metal dispersion and low active surface area, therefore limiting the overall catalytic activity. In view of further practical application of the EPOC phenomenon to industrial catalysts, we should be able to enhance the activity of nanodispersed materials. In this study, for the very first time, we observed an enhanced catalytic activity of a Pd nanodispersed catalyst supported on a porous Co₃O₄ semiconductor film. The Pd/Co₃O₄ composite powder was deposited on an yttria-stabilized zirconia (YSZ) solid electrolyte without the presence of an interlayer film. The observed enhancement was non-Faradaic, with apparent Faradaic efficiency values as high as 80. The Pd/Co₃O₄ catalyst was characterized thoroughly by means of a wide variety of physicochemical techniques, such as TEM, SEM, TGA, ICP and BET. Using supported catalysts as catalytic films for electrochemical promotion studies may lead to the practical utilization of EPOC in the chemical industry or in gas exhaust treatment.

References:
[1] C.G. Vayenas, S. Bebelis, I.V. Yentekakis, H.G. Lintz, Catal. Today. 11 (1992) 303-438.\n[2] C.G. Vayenas, S. Bebelis, C. Pliangos, S. Brosda, D. Tsiplakides Electrochemical Activation of Catalysis: Promotion, Electrochemical Promotion and Metal-Support Interactions, Kluwer Academic/Plenum Publishers, New York, 2001.\n[3] C.G. Vayenas, J. Solid State Electrochem. 7-8 (2011) 1425-1435.\n[4] C. Jimenez-Borja, S. Brosda, F. Matei, M. Makri, B. Delgado, F. Sapountzi, D. Ciuparu, F. Dorado, J.L. Valverde, C.G. Vayenas, Appl. Catal. B Environ. 128 (2012) 48-54.

SESSION: PhysicalFriAM-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Fri Oct, 25 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Ioannis Yentekakis; Philippe Vernoux; Session Monitor: TBA

11:20: [PhysicalFriAM01] Plenary
Electrochemical Promotion of Catalysis over Dispersed Nanoparticles
Philippe Vernoux¹ ; ¹University LYON 1, Lyon, France;
Paper Id: 10 [Abstract]

Electrochemical Promotion of Catalysis (EPOC) or non-Faradaic electrochemical modification of catalytic activity (NEMCA) is a promising concept for boosting catalytic processes and advancing the frontiers of catalysis. This innovative field, discovered by the group of Professor C.G. Vayenas in the early 80s [1], aims to modify operando both the activity and the selectivity of catalysts, in a reversible and controlled manner. More than 80 different catalytic systems (total and partial oxidations, hydrogenations, dehydrogenations, isomerisations, and decompositions) have been electrochemically promoted on metal or metal oxide catalysts supported on different ionic conductors [2,3]. These include reaction systems of critical importance in diverse fields of chemical synthesis including the production of commodity and fine chemicals and in the abatement of automotive emissions. EPOC utilises solid electrolyte materials (ionically conducting ceramics) as catalytic carriers. Ions contained in these electrolytes are electrochemically supplied to the catalyst surface and act as promoting agents to modify the electronic properties of the catalyst in order to achieve optimal catalytic performance. Different types of ions such as O^2-, Na⁺, H⁺, K⁺ have been successively used in the literature to boost catalytic properties of catalytic materials. It thus provides a unique means of varying promoter levels at the metal surface under reaction conditions by simply changing the potential of the catalyst film. Therefore, EPOC can be considered as an electrically controlled catalyst-support interaction in which promoting ionic agents are accurately supplied onto the catalytic surface by electrical potential control. The main technological issue of EPOC is related with the use of continuous metallic coatings interfaced onto dense solid electrolyte supports. On that account, the metallic dispersion of the catalyst-electrodes, and therefore their catalytic activity, is usually far lower than that of commercial dispersed catalysts. In addition, the thermal stability of continuous metallic coatings is rather low to the sintering phenomenon, especially when using transition metals. This explains why most of the EPOC studies reported in the literature have been performed on Platinum Group Metals (Pt, Pd, Rh) and to a lesser extent on Ag, Ru and Ir. The utilization of pure precious metals catalytic layers is not economically reliable. Furthermore, the thermal stability of pure transition metals coatings deposited on dense solid electrolyte supports is too low to be realistically implemented for catalytic processes. Therefore, some research efforts are focused to achieve EPOC over catalytic dispersed nanoparticles. This plenary lecture will give an overview of recent advances in the quest of electro-promoted nanoparticles including innovative architectures of catalyst-electrodes.

References:
[1] M. Stoukides and C.G. Vayenas, J. Catal., 70 (1981) 137.
[2] C.G. Vayenas, Electrochemical Activation of Catalysis: Promotion, Electrochemical Promotion, and Metal-Support Interactions, Springer, 2001.
[3] P. Vernoux, L. Lizarraga, M.N. Tsampas, F.M. Sapountzi, A. De Lucas-Consuegra, J.L. Valverde, S. Souentie, C.G. Vayenas, D. Tsiplakides, S. Balomenou, E.A. Baranova, Chem. Rev. 113 (2013) 8192.