Philippe Vernoux

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.

[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.