NiAl2O4-derived active sites over Ni/Al2O3 catalysts for dry reforming of methane: Temperature-dependent interplay between support morphology and thermodynamic driving forces

The formation of NiAl 2 O 4 during calcination and the subsequent generation of Ni–oxygen vacancy (Ni–Ov) interfaces during H 2 reduction play a crucial role in suppressing coke formation in the dry reforming of methane (DRM). We discovered that these catalyst characteristics are significantly influenced by calcination temperatures and macroporosity. In this study, we synthesized macroporous and non-macroporous Ni/Al 2 O 3 catalysts, which were then calcined at both mild and high temperatures to examine their structural evolution and catalytic performance in DRM. At a calcination temperature of 600 °C, the macroporous Al 2 O 3 enhanced the formation of NiAl 2 O 4 due to geometric effects and a higher AlO 4 /AlO 6 ratio. This provided a structurally favorable environment for Ni–Al interaction, even under thermodynamically limited conditions. Conversely, at 800 °C, the energy barrier for NiAl 2 O 4 formation was removed, resulting in similar spinel NiAl 2 O 4 formation irrespective of support morphology. Complementary calculations using a pretrained atomistic model supported our experimental findings, indicating that Ni incorporation is energetically more favorable in Al 2 O 3 structures with higher octahedral vacancy proportions, as seen with the macroporous support. Catalytic evaluation in DRM at 800 °C showed that the catalysts calcined at 800 °C exhibited the highest carbon balances (98–99%) and negligible coke deposition, whereas at 600 °C the macroporous catalyst showed a higher spinel fraction than the non-macroporous catalyst (0.24 vs 0.18 from H 2 -TPR) together with improved coke resistance and more stable performance. Catalysts rich in NiAl 2 O 4 and Ni–O v interfaces promoted efficient CO 2 activation and coke gasification, leading to improved reaction stability and coke resistance. • Macroporous and non-macroporous Ni-based catalysts were synthesized at various calcination temperatures. • The 600 °C calcination demonstrated a geometric effect on the formation of NiAl 2 O 4 in macroporous supports. • The 800 °C calcination was sufficiently high to overcome the geometric barrier of the NiAl 2 O 4 formation. • Catalysts calcined at 800 °C demonstrated improved stability and a superior carbon balance. • Ni–oxygen vacancy interfaces effectively suppressed coke formation during the dry reforming of methane.