Abstract
Electrochemical Promotion of Catalysis (EPOC) with alkali ionic conductors has been widely studied in literature due to its operational advantages vs. alkali classical promotion. This phenomenon allows to electrochemically control the alkali promoter coverage on a catalyst surface in the course of the catalytic reaction. Along the study of this phenomenon, a large variety of in situ and ex situ surface analysis techniques have been used to investigate the origin and mechanism of this kind of promotion. In this review, we analyze the most important contributions made on this field which have clearly evidenced the presence of adsorbed alkali surface species on the catalyst films deposited on alkaline solid electrolyte materials during EPOC experiments. Hence, the use of different surface analysis techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), or scanning tunneling microscopy (STM), led to a better understanding of the alkali promoting effect, and served to confirm the theory of electrochemical promotion on this kind of catalytic systems. Given the functional similarities between alkali electrochemical and chemical promotion, this review aims to bring closer this phenomenon to the catalysis scientific community.
Highlights
In the case of electrochemical catalysts based on alkali (M+ )-conductors, the application of electrode, which is deposited on one side of the electrolyte, and an inert counter electrode (typically a cathodic polarization between the catalyst film-working gold) located at the opposite side leads to the migration of promoter (M+) ions to the electrode, which is deposited on one side of the electrolyte, and an inert counter electrode
To induce a permanent effect and showed to be more stable than potassium carbonates effectseemed and showed to be more stable than potassium carbonates or bicarbonates, since the latter needed bicarbonates, since the latter needed lower positive potentials to be decomposed. These results lowerorpositive potentials to be decomposed. These results demonstrated that the nature of the final demonstrated that the nature of the final form of alkali promoter species and their chemical structure form of alkali promoter species and their chemical structure
It is well known that alkali promoters play a key role in heterogeneous catalysis with special
Summary
Promoters are widely used in the heterogeneous catalysis field [1,2]. Structural promoters improve the dispersion and stability of the active phase on the catalyst support, while electronic ones enhance the catalytic properties of the active phase itself. When using ionic conductor materials there are important differences in operating EPOC systems depending on the nature of the employed where the supplied ions can participate in the catalytic reaction under study Both or H+ ions in catalytic hydrogenations) these ions act as “sacrificial promoters” and present a galvanostatic and potentiostatic operations allow to obtain a steady-state catalytic reaction rate at finite mean residence time on the catalyst surface In these cases, both galvanostatic and potentiostatic each applied current or potential, respectively.
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