PARTIAL LIQUID-PHASE HYDROGENATION OF BENZENE TO CYCLOHEXENE OVER RUTHENIUM CATALYSTS IN THE PRESENCE OF AN AQUEOUS SALT SOLUTION .2. INFLUENCE OF VARIOUS SALTS ON THE PERFORMANCE OF THE CATALYST

The research described in this article forms a continuation of the investigations reported in part I [J. Struijk, M. d'Angremond, W.J.M. Lucas-de Regt and J.J.F. Scholten, Appl. Catal. A, 83 (1992) 263], concerning the batch-wise partial hydrogenation of benzene to cyclohexene in a stirred autoclave at 423 K and a pressure of 5.0 MPa, over ruthenium catalysts and in the presence of an aqueous salt solution. In the present part, the study of the influence of various variables on the performance of the catalyst is continued. Attention is paid to the influence of the type of reaction-modifying salt, its concentration, the method of pretreatment of the catalyst, the pH of the aqueous phase and the influence of iron deposition from the inner wall of the reactor on the surface of the catalyst. Fresh and used catalysts were characterized by BET surface area measurements, X-ray photoelectron spectroscopy/Auger electron spectroscopy analysis, atomic absorption spectroscopy and temperature-programmed reduction. From these characterizations the coverage of the ruthenium catalysts with the reaction-modifying salts could be determined. As stated before, the primary function of the adsorbed salts appears to be the transformation of the hydrophobicity of the ruthenium catalyst particles into hydrophilicity. Several salts can be used as a reaction-modifier, provided their adsorbability on ruthenium is high enough and reduction of the chemisorbed cations under the experimental conditions does not occur. Effective modifying salts are, for instance, chromium (II) sulphate, manganese (II) sulphate, iron (II) sulphate, cobalt (II) sulphate, nickel (II) sulphate, zinc (II) sulphate, zinc (II) chloride and gallium (III), cadmium (II) and indium(III) salts.