Coke-resistant Ni/Al2O3 catalysts for low-temperature dry reforming of methane via Ni0/NiAl2O4 interface control

The dry reforming of methane (DRM) is a key process for valorizing CO 2 and CH 4 , yet the catalyst longevity is limited by severe coking at low temperature. Among various catalysts studied, NiAl-based systems have been a long-standing research focus due to their inherent advantages. However, their practical application has been perpetually hampered by vulnerability to coke formation. This study investigates the effect of varying the Ni 0 /Ni 2+ ratio (from NiAl 2 O 4 ) in a 5 wt.% Ni/Al 2 O 3 catalyst, while controlling particle size and Ni dispersion, on coke resistance under conditions where carbon formation is thermodynamically favored, i.e., 600 o C, CH 4 :CO 2 :N 2 = 25:25:10, GHSV = 150 L g cat -1 h -1 . Using in situ XANES, we established that a catalyst formulation, Ni 0 /NiAl 2 O 4 /Al 2 O 3 , with 32.5% Ni 0 and 67.5% Ni 2+ achieves the highest performance. Comprehensive pulse experiments and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) provides insights into the reaction mechanism, wherein CH x * (* adsorbed) species from CH 4 dissociation on Ni 0 are rapidly oxidized by the surface O* from NiAl 2 O 4 to form HCO 3 * and CO 3 * intermediates. Simultaneously, the CO disproportionation route to coke is suppressed. In contrast, a catalyst lacking this optimized interface readily promotes coke deposition. Coke-resistant low-temperature dry reforming of methane is achieved by precisely tuning the Ni 0 /NiAl 2 O 4 interfacial structure on Ni/Al 2 O 3 catalyst. An optimized catalyst with 32.5% Ni⁰ and 67.5% Ni 2+ enables rapid oxidation of CH x * intermediates into bicarbonate and carbonate species, suppressing carbon accumulation under thermodynamically unfavorable conditions. • Ni 0 /NiAl 2 O 4 /Al 2 O 3 enables coke-resistant low-temperature DRM. • Optimal 32.5% Ni 0 on Ni 0 /NiAl 2 O 4 /Al 2 O 3 maximizes the catalytic stability. • CH x species are oxidized into bicarbonates by active oxygen species. • CO disproportionation is effectively suppressed. • Stable DRM performance is achieved at 600 °C under 150 L g cat -1 h -1 .