CH4 conversion into value-added products by catalytic processes assisted by electrochemical reactions in solid oxide cells

Abstract

Methane (CH4), the major constituent of natural gas and biogas, is an abundant source to obtain value-added hydrocarbons. The oxidative coupling of methane (OCM) is a direct catalytic route to convert CH4 towards C2 hydrocarbons (C2H6 and C2H4). The use of electrochemical devices such as solid oxide fuel cells (SOFC) as a reactor for OCM is possible, providing synergistic control of electrochemical oxidation/reduction reactions to energy production with in-situ catalysis [1]. In this context, the use of mixed oxide La0.5Ce0.5O2-δ (LCO) was studied as an additional catalytic layer on the Ni/YSZ anode of a SOFC for the operation under CH4 as fuel. The presence of surface oxygen vacancies in single-phase LCO, which may benefit the OCM reaction, was evidenced by Raman spectroscopy [2]. The catalytic properties of LCO at 800 ºC were investigated in a fixed-bed catalytic reactor, resulting in a C2 selectivity and yield of 41% and 8%, respectively. The modified SOFC with the additional LCO-catalytic layer was fabricated and tested under H2 and CH4 [2]. The electrochemical properties were studied during online gas analysis of the anode outlet. The experimental data revealed that CH4 conversion and product distribution are closely related to operational conditions such as reactant concentration, anode feed flow rate, current output, and operating temperature. In addition to C2, products of internal methane reforming (CO and H2) were detected in all evaluated conditions. The SOFC showed stable behavior, maintaining a stable current of 20 mA·cm-2, 10% of CH4 conversion, and 14% of C2 selectivity throughout 30 h. The combined catalytic and electrochemical reactions described are considered a promising approach to producing valuable chemicals and electrical energy.