(638c) Enhanced Methane Conversion in Chemical Looping Partial Oxidation to Syngas Using Copper, Cobalt and Nickel Doping Modification with Density Functional Theory Calculation

Biomass-generated methane is a renewable and sustainable energy source for the synthesis of syngas and value-added chemicals. It is a topic of immense academic and industrial interest because it is now economically and commercially viable to obtain biomass-generated methane with a quality similar to fossil natural gas. Chemical looping partial oxidation (CLPO) is a promising strategy of methane conversion to syngas with low cost and minimal environmental impact. The core of chemical looping technology depends on complex redox reactions involving hydrocarbon molecules absorption and dissociation on metal-oxide based oxygen carrier surfaces, lattice oxygen ion diffusion, oxygen vacancy creation and annihilation at high temperatures. The cycles of chemical looping partial oxidation (CLPO) process allows continuous generation of high purity syngas with a controllable CO to H₂ ratio and a near-zero CO₂ emission. A major challenge is the development of oxygen carriers that have high reactivity, high oxygen carrying capacity, and recyclability. We demonstrate that the addition of a low concentration of copper, nickel, or cobalt dopant to iron-based oxygen carriers can dramatically enhance the reactivity in CLPO process at low temperatures while maintaining the recyclability of these carriers. Doped iron oxides are fabricated by sol gel or solid-state synthesis. Afterwards, X-ray Diffractometry (XRD), Scanning electronic microscopy (SEM)/ Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were utilized to determine the structural and morphological modification of iron oxide. The lattice parameters and surface functional groups of iron oxide variation indicate the existence and functions of these dopants. The redox reaction and temperature programming reaction (TPR) are conducted with fuel gases by thermogravimetric analysis (TGA) with Mass spectrometry (MS). These results are substantiated by ab initio DFT+U and thermodynamics analyses. It is noted that operating a chemical looping system at lower temperature can result in energy consumption savings of ~20% as compared to a chemical looping operation at 950°C or higher. Thus, our findings provide a pathway to significantly lowering the methane reaction temperature in chemical looping systems, which will lead to substantial energy savings with desired oxygen carrier recyclability.