Catalytic activity of Cr- or Co-modified Ni-based rapidly quenched alloys in the hydrogenation of isophorone

Raney-type Ni-based catalysts containing a small amount of Cr or Co were prepared from Ni32-xAl68Crx and Ni32-xAl68Cox (x = 1, 3 or 6) rapidly quenched alloys by leaching in 1 M NaOH. These degradation processes occurring at the surface and in the bulk of the alloys were used for promoting the catalytic activity of these materials. The modifications of the internal structure, chemical composition and morphology of the alloys proved to be a useful method for transforming inactive Ni-Al-Cr and Ni-Al-Co alloy precursors into active and selective catalysts. The hydrogenation of isophorone (3,5,5-trimethyl-2-cyclohexen-1-one) was used as a catalytic test for the modified materials. The catalytic tests showed that the conversion of isophorone hydrogenation increases with temperature but decreases with the addition of Cr or Co to the Ni-Al alloy. Conversely, selectivity to dihydroisophorone (3,3,5-trimethylcyclohexanone) formation drops with temperature but for Cr- or Co-containing catalysts it is distinctly higher than for that of a conventional Raney Ni catalyst. The most promising catalyst seems to be that obtained from Ni-Al-Cr, alloy: it is characterized by both high conversion and high selectivity. Further hydrogenation of dihydroisophorone to homomenthol (3,3,5-trimethylcyclohexanol) appeared to be strongly restrained on the above catalysts and the reaction did not proceed even after 7 days under p = 70 atm. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) allowed the changes occurring during the activation process to be identified, and their implications for catalytic function to be considered. (C) 2009 Elsevier B.V. All rights reserved.