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 gamma-Al-2-O-3 (Ni/-gamma-Al2O3). 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 Al2O3 catalysts contained NiAl2O4 species after calcination, while the Ni/-gamma-Al2O3 catalyst contained NiO and NiAl2O4 species after calcination. Although the Ni/gamma-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 degrees C for 31 h, and maximum dispersions of similar to 10%, after reduction at 650 degrees C for 7 h. After reduction at 550 degrees C, the Ni particles were not evident by TEM examination. The results suggest that the formation of a surface NiAl2O4 spinet phase during preparation is beneficial for a high Ni dispersion in the reduced catalyst. (c) 2005 Elsevier B.V. All rights reserved.