CO2 reforming of methane over Ni-Al-LDH catalysts prepared with different precipitants

Abstract

NiAl-LDH catalysts were synthesized using the co-precipitation method with different precipitant. One of the samples (NiAl_C) was prepared with a Na₂CO₃ solution, while the other sample (NiAl_M) was prepared with a mixture of Na₂CO₃ and NaOH. These catalysts were evaluated in the dry reforming of biogas, utilizing a synthetic biogas consisting of 60 % (v/v) CH₄ and 40 % CO₂. Characterization techniques including X-ray diffractometry (XRD), N₂ adsorption-desorption, thermogravimetric analysis (TGA), and temperature-programmed reduction and oxidation (H₂-TPR and TPO, respectively), NH₃, CO₂, and H₂ desorption (NH₃-TPD, CO₂-TPD, and H₂-TPD, respectively) where used in different stages of catalysts. Both samples resulted in LDH with small differences in cell parameter c and specific surface area. The precipitant containing NaOH led to an increase in the NiAl₂O₄ spinel phase and in the metallic dispersion of NiAl_M, enhancing thermal stability and resistance to sintering. However, this elevated metallic area facilitated the presence of acid sites, promoting CH₄ decomposition and carbon deposition. The reduction step proved unnecessary for this catalyst, as the reduced catalyst led to an increase in structured carbon formation. The delicate balance between thermal stability and carbon deposition favors the NiAl_M sample under reaction conditions without the reduction step.