Active site-controlled coke speciation on nickel catalysts for the dry reforming of methane via the tuning of Ni particle size and oxygen vacancy on Ni-Al2O3 interfaces

초록

The performance of Ni/Al2O3 catalysts in the dry reforming of methane (DRM) is governed by Ni particle size, and by the interfacial oxygen environment surrounding the active Ni sites. In this study, three Ni-based catalysts, Ni-A, Ni-B, and Ni-C, are designed to generate different Ni precursor structures, and in consequence, different reduced-state Ni active sites. This is achieved by combining non-macroporous or macroporous Al2O3 supports with impregnation or one-pot synthesis routes, thereby tuning the formation of isolated NiO, interacting NiO, and NiAl2O4-derived precursors. The average Ni particle size decreases from (12.8 to 7.3 and 5.5) nm for Ni-A to Ni-B and Ni-C, while the interface ratio increases from (33.9 to 52.1 and 60.2) %, respectively, representing progressively stronger Ni-support interaction. Combined structural and electronic analyses reveal three distinct active-site populations: large Ni on oxygen vacancy (Ov)-free Al2O3 (site I), small Ni on Ov-free Al2O3 (site II), and small Ni on Ov-rich Al2O3 (site III). Among them, Ni-C, enriched on site III, exhibits the best DRM performance, maintaining about (90-91) % CH4 conversion, (96-97) % CO2 conversion, and a carbon balance close to (98-99) % after 90 h time-on-stream. In contrast, Ni-A, dominated by site I, undergoes severe deactivation and favors graphitic coke formation, whereas Ni-B, enriched in sintering-evolved site II, shows the strongest tendency toward CNT-like coke. These results demonstrate that the decisive factor in DRM is the identity of the Ni active site, where the coupling between Ni size and interfacial Ov determines catalytic stability and coke evolution.

키워드