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 (NiB₂O_4-x, B = Mn, Fe, Co) featuring 3D spherical architectures and abundant oxygen vacancies. Among these materials, NiMn₂O_4-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 NiFe₂O_4-x and NiCo₂O_4-x, NiMn₂O_4-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 NiMn₂O_4-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 NiMn₂O_4-x preferentially followed the CH_xO 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.