Selective conversion of sorbitol to glycols and stability of nickel-ruthenium supported on calcium hydroxide catalysts

Supported catalysts based on ruthenium have been prepared to study the hydrogenolysis of sorbitol to selectively obtain glycols in an alkaline medium. Among the tested catalysts, ruthenium impregnated directly over Ca(OH)(2) exhibited a yield of glycols higher than that of ruthenium supported on an alumina catalyst where the alkali promoter was added separately to the reaction medium. When nickel was incorporated into the calcium hydroxide supported ruthenium catalyst a promoting effect was observed, which was explained by an electronic interaction between both metals. A glycol yield of approximately 40% was accomplished after 4h of reaction. A number of physicochemical techniques, such as evolved gas analysis by mass spectrometry (EGA-MS), temperature programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and total reflection x-ray fluorescence (TXRF) analysis, were used to characterize fresh and used catalysts. The stability of the NiRuCa catalyst showing the best performance was examined. It was found that it was not stable in the reaction medium because of solubilization of the basic support Ca(OH)(2) during the reaction progress. A substantial improvement of the stability was accomplished if the amount of Ca(OH)(2) solubilized during the reaction is externally incorporated prior to conducting the reaction. (C) 2015 Elsevier B.V. All rights reserved.