CO2 utilization and on-purpose ethylene production: a chemical looping approach

Abstract

CO2-assisted ethane dehydrogenation (CO2-ODHE) is a promising carbon atom economy process for upgrading CO2 to CO in tandem with C2H6 to C2H4 conversion. Iron oxide-based materials are selective for on purpose ethylene production through CO2-ODHE. The feed admission mode was found to play an important role on catalytic performance. Alternating C2H6 (reduction step) and CO2 (oxidation step) feedstock to a fixed bed reactor (chemical looping concept, CO2-ODHE-CL) attained constant ethane and CO2 conversion per step at 600oC, equal to ~17.6%, while C2H4 selectivity during the reduction step was ~75%. The lattice oxygen mobility is a descriptor for the materials used during the CO2-ODHE-CL, since low mobility resulted in an increased C-H bond scission selectivity, i.e., C2H4 production, during the reduction step. Temperature programmed 18O2 isotope exchange experiments, along with temperature programmed H2 – reduction, were employed to exemplify the latter statement, investigating the lattice oxygen reactivity of the examined materials and the mechanism through which the lattice oxygen is reacting. X-ray techniques (X-ray Diffraction, X-ray Raman Scattering Spectrometry, X-ray Absorption Spectrometry) along with structural modeling demonstrated that the formation of a spinel like arrangement between Mg and Fe, stabilized lattice oxygen and thus minimized the undesired C-C bond scission during the C2H6 step of CO2-ODHE-CL.