Textural and Structural Analyses of Industrial Raney Nickel Catalyst

Abstract

In this work, the influence of the temperature (60, 80, and 110 °C) in the production of Raney Ni catalysts was addressed. The catalysts were obtained by alkaline leaching of a Ni−Al alloy, and both the Ni−Al alloy and the leaching process that was evaluated were provided by an industrial partner. The physical−chemical properties of the catalysts were investigated by X-ray diffraction (XRD), scanning and transmission electron microscopies (FEG-SEM and TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption, and small-angle X-ray scattering (SAXS) techniques. In particular, a comparison between SAXS and N2 adsorption results about the textural properties is discussed. The three Raney Ni catalysts presented the typical highly porous metallic nickel structure. The analysis of the surface, however, suggested the presence of major contributions of NiO, Ni(OH)2/Ni2O3, and Ni−O−Al species in all samples and the presence of Ni0 for the samples produced at 60 and 80 °C. The two samples prepared at lower temperatures presented similar characteristics: crystalline domains of 50 and 60 Å, BET specific surface area of 58 and 65 m2 g−1, and porosity of 0.100 and 0.107 cm3 g−1, respectively. These properties appear to be more interesting for catalytic purposes than the characteristics of the catalyst prepared at 110 °C: mean crystalline size of 100 Å, BET specific surface area of 51 m2 g−1, and pore volume of the 0.097 cm3 g−1. A higher concentration of Al species, about 80 atom %, however, was also observed on the surface of the catalysts produced at 60 and 80 °C. The larger pores found in the catalyst produced at 110 °C may have facilitated the removal of the Al species during the washing process and are probably related to the larger Ni crystalline domains in this sample.