NiB₂O_4-x Nanospheres for Methane Dry Reforming to Hydrogen-Rich Syngas

Methane dry reforming (DRM) is an effective method for simultaneously treating two predominant greenhouse gases: methane (CH4) and carbon dioxide (CO2). However, it encounters challenge due to the low hydrogen content in the produced syngas, which hinders its industrial applications. Spinel serves as highly effective oxygen carrier with substantial oxygen storage capacity, facilitating the production of hydrogen-rich syngas in methane chemical looping reforming. Consequently, this research conducted a comparative analysis of the DRM performance of distinct B-site metal nickel-based spinel materials (NiB2O4-x, B = Mn, Fe, Co) featuring 3D spherical architectures and abundant oxygen vacancies. Among these materials, NiMn2O4-x achieved conversion rates of CH4 and CO2 nearing 80% at 700 °C, and the resulting syngas exhibited exceptional characteristics with a H2/CO molar ratio of about 1.2. Compared to NiFe2O4-x and NiCo2O4-x, NiMn2O4-x exhibited a higher concentration of Mn3+ and Mn4+ ions, leading to a more abundant redox process. Moreover, its strong ability to store and release oxygen species increased the concentration of reactive oxygen species on the catalyst surface. Additionally, the appropriate surface acidity and basicity enhanced the CH4 conversion capability of NiMn2O4-x and increased the H2/CO ratio. In situ Diffuse Reflectance Infrared Spectroscopy (in situ DRIFTS) integrated with theoretical calculations (DFT) corroborated that the DRM reaction associated with NiMn2O4-x preferentially followed the CHxO pathway. This study offers insights into the production of hydrogen-rich synthesis gas and establishes a foundation for investigating the mechanism of lattice oxygen activation.