Dynamic Electrochemical Promotion of Catalysis
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Abstract
Electrochemical Promotion of Catalysis (EPOC) is a method for enhancing a catalytic reaction by modifying the surface properties of the catalyst through the application of a small amount of current or interfacial potential. It can also be used to enhance the selectivity of heterogenous catalytic reactions. It was first discovered by M. Stoukides and C. Vayenas in early 1980s. This phenomenon can increase the catalytic rate by 10 to 10^5 times compared to the electrochemical rate of supply of ions to the catalyst which is given by Faraday’s law. Therefore, the process is no longer faradaic and hence, it is also known as “Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA)".
Today, the EPOC mechanism has been widely researched by different research groups, and many reactions have been investigated, but unfortunately, no commercial application of the technology is available. The main problem with EPOC is the lower activity per unit mass of the catalyst compared to the commercially used catalysts in conventional reactors. This drawback has been hindering the commercialisation of this idea.
A new route has been proposed, which is called "Dynamic Electrochemical Promotion of Catalysis (DEPOC). The difference between EPOC and DEPOC comes from the dynamic operation of the system. In DEPOC, the current or the potential over the catalyst is varied periodically at different frequencies, symmetries and amplitudes of the wave-forms. This periodic modification is expected to have a role on selectivity of products and reaction rate.
The main application that is considered for this mechanism is the Fischer-Tropsch (FT) reaction. It is a polymerization process which leads to hydrogenation of carbon monoxide forming liquid hydrocarbons. Controlling the selectivity of this reaction is hard, and normally a wide distribution of carbon chain lengths are obtained. With periodic application of voltage on the DEPOC catalyst, it is expected to be able to control the selectivity of the reaction or in other words the product distribution of the reaction.
In this thesis, the DEPOC effect will be mainly studied from a theoretical perspective. First, the EPOC phenomenon will be analysed and the theory will be extended to the DEPOC effect. The study will be based on understanding the thermodynamics and the kinetics of these mechanisms. Lastly, a conceptual reactor design approach will be studied for the process.