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

Abstract

Three Ni–Al 2O 3 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 Al 2O 3), and impregnation on a commercial γ-Al 2O 3 (Ni/γ-Al 2O 3). The catalysts were characterized by N 2 physisorption, H 2 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 Al 2O 3 catalysts contained NiAl 2O 4 species after calcination, while the Ni/γ-Al 2O 3 catalyst contained NiO and NiAl 2O 4 species after calcination. Although the Ni/γ-Al 2O 3 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 Al 2O 3 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 NiAl 2O 4 spinel phase during preparation is beneficial for a high Ni dispersion in the reduced catalyst.