(536m) Exploring LaFeO3 oxygen Carriers for Reactivity Enhancement through Structural Changes in Chemical Looping Partial Oxidation System

Improvements in the utilization of hydrocarbon feed to produce syngas, a valuable intermediate, have always been sought-after in the industry. Chemical looping partial oxidation (CL-POX) is a promising pathway for syngas production due to its superior reaction thermodynamics and energy efficiencies compared to conventional technologies. However, the success of CL-POX lies in its oxygen carrier, as it provides the oxygen required for the reaction, and controls the product yield. Several micro-sized oxygen carriers have been developed for conducting the CL-POX reaction. However, because of their low specific area and pore volume, the reaction kinetics tend to get suppressed. Thus, there is a research thrust in developing nano-sized oxygen carriers to enhance the kinetics.

In this work, LaFeO₃ nanoparticles were synthesized for carrying out the CL-POX reaction by embedding them in mesoporous SBA-15 support (LaFeO₃@SBA-15). For comparison micro-sized LaFeO₃ sample impregnated on SiO₂ support (LaFeO₃@SiO₂) was also synthesized. Thermogravimetric experiments (TGA) employing methane as reducing gas showcased that LaFeO₃@SBA-15 maintained stable performance over 15 redox cycles with nearly 1000% improvement in reaction rate compared to LaFeO₃@SiO₂. In addition, characterization techniques such as X-ray diffraction (XRD), nitrogen physisorption, and high-resolution transmission electron microscopy (HR-TEM) were used to investigate this dramatic increase in reaction rate. The analysis revealed that LaFeO₃ forms a different crystal structure when embedded in SBA-15 as opposed to SiO₂. This can be attributed to the mesoporous, tubular, and ordered structure of SBA-15 which enabled the formation of nano-scaled particles and stabilized a more active LaFeO₃ crystal structure. To corroborate the experimental results and explore the reaction mechanism over the different crystal structures, atomistic level-based density functional theory calculations were carried out. The findings from this study provide vital insights into the role of crystal structure in reaction kinetics and thus can be leveraged to develop highly active chemical looping oxygen carriers.