Roles of metal oxide overlayers on hydrotalcite-structured Ni-MgAlOx for dry reforming of CH₄ with CO₂

The thermal stability of Ni nanoparticles on the coprecipitated hydrotalcite-like Ni-MgAl₂O₄ (NiMgAl) was enhanced by simply introducing an overlayer coating method with four different metal oxides (M) such as CeO₂, ZrO₂, SiO₂ and Al₂O₃ (NiMgAl@M) for a harsh dry reforming reaction of CH₄ with CO₂ (DRM). Among the catalysts, the superior catalytic properties on the NiMgAl@Al such as less sintering and coke deposition were originated from the much stronger metal support interaction (SMSI), which were originated from the formed spatially confined Ni nanoparticles on the MgAl₂O₄ frameworks through the possible exsolution phenomena with the help of the porous Al₂O₃ overlayers. The unmodified NiMgAl catalyst revealed a relatively lower catalytic activity due to the facile coke depositions, which was mainly caused by the selective formation of larger Ni nanoparticles above 25 nm with its heterogeneous size distribution. The much simpler overlayer coating method with the porous overlayer structures, especially for Al₂O₃ coating layer, was found to be an effective way to achieve a superior catalytic activity and stability by preserving the thermally stable smaller Ni nanoparticles on the hydrotalcite-like Ni-MgAl₂O₄ surfaces.