Kinetic study of CO2 hydrogenation on Ru/ YSZ catalyst using a monolithic electropromoted reactor (MEPR)

Abstract

The majority of the kinetic studies reported in the literature for heterogeneously catalyzed reactions, take place on laboratory scale reactors. In the present study, the kinetic mechanism of electrochemical promotion of CO2 hydrogenation was investigated using a scaled up, monolithic electropromoted reactor (MEPR) loaded with nine parallelly connected Ru/YSZ/Au electrochemical cells. The study was carried out under atmospheric pressure, at 370 °C, with a flowrate of 1000 cm3/min and over a wide range of reactants partial pressures. The morphological and electronic characteristics of the catalyst surface, before and after reaction, were thoroughly investigated with a variety of techniques including X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). It was shown that increasing the partial pressure of H2 (electron donor) leads to an increase in the methane production rate with a concurrent decrease of CO formation. Methanation emerges with a positive order in H2 whereas the RWGS with a negative one. Increasing the partial pressure of electron acceptor (CO2) leads to the opposite behavior. Based on the kinetic results and the rules of chemical and electrochemical promotion, an electrophobic behavior (increase of the rate with increasing catalyst potential) is expected for the methanation reaction and an electrophilic (decrease of the rate with increasing catalyst potential) for the RWGS reaction. Both predictions are confirmed experimentally. The results are in agreement with previous studies on CO2 hydrogenation in laboratory scale reactors demonstrating the successful design and operation of the current scaled up electropromoted system (MEPR).