Comparison of reducibility and stability of alumina-supported Ni catalysts prepared by impregnation and co-precipitation

Three Ni–Al2O3 catalysts, with nickel loadings of 10–13 wt.%, were prepared by co-precipitation (Ni–Al co-precip), impregnation on an in-house sol–gel derived alumina (Ni/sol–gel Al2O3), and impregnation on a commercial γ-Al2O3 (Ni/γ-Al2O3). The catalysts were characterized by N2 physisorption, H2 chemisorption, TPR, XRD, SEM and TEM. The Ni species, Ni particle size, and Ni reducibility depended on the preparation method. The Ni–Al co-precip and Ni/sol–gel Al2O3 catalysts contained NiAl2O4 species after calcination, while the Ni/γ-Al2O3 catalyst contained NiO and NiAl2O4 species after calcination. Although the Ni/γ-Al2O3 catalyst was the easiest to reduce, according to TPR, this catalyst had the lowest hydrogen uptake over a 100 h temperature-staged reduction experiment. The Ni–Al co-precip and Ni/sol–gel Al2O3 catalysts had Ni dispersions of over 7% with reduction at 550 °C for 31 h, and maximum dispersions of ∼10%, after reduction at 650 °C for 7 h. After reduction at 550 °C, the Ni particles were not evident by TEM examination. The results suggest that the formation of a surface NiAl2O4 spinel phase during preparation is beneficial for a high Ni dispersion in the reduced catalyst.