Methane partial oxidation with Ni-Mg-Al hydrotalcites: Impact of magnesium on catalyst performance

The partial oxidation of methane (POM) is a promising route for hydrogen-rich syngas production with lower energy requirements compared to steam reforming. Herein, Ni-incorporated Mg-Al hydrotalcite-derived mixed oxide catalysts (5Ni-HT-x, x = 60, 65, 70, 75 wt.% Mg) were synthesized via co-precipitation and evaluated for CH₄ conversion and H₂ yield. Characterization techniques, including X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), BET, H₂-TPR, TEM, FTIR, TGA, and Raman spectroscopy, were employed to investigate catalyst structure, active site stability, and carbon deposition. As a constituent of hydrotalcite-derived mixed oxides (HT), Ni2+ is strongly bound within the hydrotalcite-derived mixed oxides structure, stabilizing the active Ni sites during the POM reaction. Upon increasing the proportion of Mg from 60% to 65% in hydrotalcite-derived mixed oxides, the surface area of the catalyst (5Ni-HT-65) reaches a maximum without changing the concentration of active sites, as well as H2 yield progresses to 45% (against 37% H2 yield over 5Ni-HT-60). Upon further raise of Mg proportion to 70%, hydrotalcite-derived mixed oxides attain the highest concentration of active sites, which catalyzes POM reaction most effectively, yields 46.2% H2 with a 2.3 H2/CO ratio during 400 mins TOS and yields 48% H2 with a 2.18 H2/CO ratio during 15 h TOS. However, excessive Mg (75 wt.%) leads to surface area loss, weakened Ni-support interaction, and increased crystalline carbon deposition, reducing catalytic efficiency. The study highlights the critical role of Mg in tuning Ni reducibility and carbon resistance, offering insights for optimizing hydrotalcite-derived mixed oxides-derived catalysts for POM applications.