High-reactive and coke-resistant polyhedral NiO/Fe2O3 oxygen carrier for enhancing chemical looping CH4–CO2 dry reforming

Abstract

Chemical looping dry reforming of methane (CL-DRM) is a promising technology for syngas production and efficient CH4 and CO2 utilization to provide appropriate H2/CO ratio in the reducer for Fischer-Tropsch synthesis. The crucial issue in CL-DRM is to find a highly reactive oxygen carrier (OC) with good stability. Polyhedral NiO/Fe2O3 composite oxygen carriers were successfully fabricated via a hydrothermal and calcination method based on different solubility product constants of nickel carbonate (NiCO3) and ferrous carbonate (FeCO3) in aqueous solution. The physicochemical properties of the OCs were characterized by XRD, XRF, SEM, TEM, TG/DTA, XPS, H2-TPR and Raman spectroscopy. The performance of NiO/Fe2O3 OCs was measured in a fixed-bed reactor. The experimental results indicated that the Fe2O3-0.6Ni OC has the highest syngas yield up to 90.25% with ideal H2/CO mole ratio (approximately 2) in the reducer at 750 °C. In addition, in reducing atmospheres, the Ni3Fe alloy was formed instead of metallic Ni and Fe, thus significantly improves coke resistance. Density functional theory (DFT) calculations demonstrated that the energy barrier of rate determining step of dehydrogenation process (CH3 releases H to form CH2) is 2.64 eV with OC of pure Fe2O3, which is higher than that of the condition with OC of NiO/Fe2O3 composite (2.21 eV). Therefore, the addition of NiO to Fe2O3 favors the CH4 dehydrogenation process on the surface of OCs. This study provides guidance for the design of oxygen carriers for chemical looping dry reforming of methane with the better coke-resistant property.