Geometrically effective NiAl2O4 formation over macroporous Ni/Al2O3 catalysts and coking resistance in dry reforming of methane

Abstract

This study aimed to investigate the geometrical effect of macroporosity on the performance of Ni-based catalysts in the dry reforming of methane (DRM). For this, macroporous Ni/Al2O3 catalysts with different Ni contents were synthesized. Characterization experiments on the macroporous Ni/Al2O3 catalysts revealed that the macroporous Al2O3 structure enhanced NiAl2O4 formation by facilitating efficient interactions between the Ni species and accessible Al2O3 sites on the macroporous wall surface during calcination. In a subsequent reduction step, Ni exsolution from the NiAl2O4 structure generated highly dispersed Ni nanoclusters over the macroporous Al2O3. Conversely, non-macroporous Ni/Al2O3 catalysts presented substantial amounts of large isolated Ni nanoparticles at an Ni content of 20 wt%, owing to limited NiAl2O4 formation caused by the lack of accessible Al2O3 sites. The highly dispersed Ni nanoclusters surrounded by oxygen vacancies on the macroporous Ni/Al2O3 catalysts significantly enhanced their catalytic performance in the DRM, evidenced by their high CO2 and CH4 conversions and strong resistance to coking. Moreover, the superior coke resistance ability of the macroporous Ni/Al2O3 catalysts was attributed to the gasification of the coke precursor on Ni nanoclusters surrounded by oxygen vacancies during the DRM.