Preparation and Characterization of Ru/Al 2 O 3 Catalysts by adsorption-precipitation-activation method and Selective Hydrogenation of Dimethyl Maleate to Dimethyl Succinate

Abstract

Supported Ru catalysts were prepared by adsorption- precipitation-activation method using RuCl 3 as Ru resource, NaOH as precipitant and Al2O3 as support. Ru(OH)3/Al2O3 was first produced in the adsorption-precipitation process, and then activated with either calcination-reduction or direct reduction by H 2 to obtain Ru/Al 2O3. The synthesized Ru catalysts were characterized with XRD, XPS, H 2-TPR techniques, and used for the catalytic hydrogenation of dimethyl maleate (DMM). It was found that the activation process strongly affected the catalytic performance. The highest hydrogenation activity was observed with catalysts activated by direct H 2 reduction, which produced the finest Ru particle on alumina. Unexpectedly, Ru metal formation was observed based on XRD and XPS data and was explained by the disproportionation reaction of Ruthenium hydroxide: 4Ru(OH) 3 = Ru + 3RuO2 + 6H2O. This explanation was also supported by the H2-TPR results of Ru(OH)3/Al2O3 samples pretreated under different conditions, and by characterization data of unsupported Ru samples. XRD data demonstrated that large particles of Ru and RuO 2 were formed upon calcination of Ru(OH)3/Al2O3 at above 200°C, and subsequent reduction of the calcined sample would give rise to Ru/Al 2O3 with larger metal crystals as compared to that of directly reduced ones.