Determination of Rate Equation for the Electrochemical Hydrogenation and Hydrogenolysis of Furfural in Acidic Media over Copper

Abstract

The use of electricity from renewable sources allows for carbon neutral electrochemical processes to be operated. One example process is that of the electrochemical hydrogenation and hydrogenolysis of furfural (FF) to furfuryl alcohol (FA) and 2-methylfuran (MF). FA is used as a reactant in making furanic polymers for molds and castings, and MF has been identified as a high octane fuel. The electrochemical reactions of FF to FA and MF occur in parallel in acidic conditions on Cu catalysts. In this work we investigated the reaction mechanism by proposing a set of elementary steps, deriving the corresponding rate equation, and fitting it to the data. A Langmuirian trend was seen in the production rate vs FF concentration data.Experimentation was done using a catholyte that contained 0.1 or 0.5 M H2SO4 with a concentration of FF between 10 and 120 mM. The potential was first varied in pH 0 with 100 mM FF to determine the Tafel slope and exchange current densities, as well as the range of potential where the reaction is not mass transfer limited. The Tafel region of the system was found to be between -517 mV and -572 mV. To determine the effect of concentration of FF, the applied potential was set to -560 mV vs RHE, where the system is limited by kinetics and not mass transfer. The reaction rates to desired products were found to change from positive order to zero order with respect to FF concentration, showing a Langmuirian trend. It was found that the plateau in the reaction rate was 50% and 58% lower for MF and FA species respectively when the pH was changed from 0 to 1. The reaction rate equation was determined to be the equation that best fit the data across both pH levels.