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Influence of Support for Ru and Water Role on Product Selectivity in the Vapor-Phase Hydrogenation of Levulinic Acid to γ-Valerolactone: Investigation by Probe-Adsorbed Fourier Transform Infrared Spectroscopy C

Velisoju, Vijay Kumar, Peddakasu, Ganga Bhavani, Gutta, Naresh, Boosa, Venu, Kandula, Manasa, Chary, Komandur V. R., Akula, Venugopal
Journal of physical chemistry 2018 v.122 no.34 pp. 19670-19677
Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, activated carbon, aluminum oxide, ammonia, catalysts, desorption, hydrogenation, levulinic acid, magnesium oxide, physicochemical properties, spectral analysis
Ru supported on activated carbon, Al₂O₃, and MgO was assessed for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). Role of H₂O on the hydrogenation activity of Ru was studied by probe-adsorbed diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy. Ru supported on activated carbon showed a maximum productivity of 1.18 kgGVL kgcₐₜₐₗyₛₜ–¹ h–¹ with an insignificant loss in the activity after 72 h of continuous operation in the presence of H₂O. Using pure LA, GVL rate was decreased by an order of magnitude (0.12 kgGVL kgcₐₜₐₗyₛₜ–¹ h–¹) within 6 h of reaction time. The physicochemical characteristics of the catalysts were examined by temperature-programmed desorption of NH₃, CO pulse chemisorption, H₂-temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques. H₂O-adsorbed DRIFT spectroscopic data revealed the reversible generation of surface −OH groups when aqueous LA was used as the substrate; consequently, Ru/C catalyst stability was also improved. Finally, on the basis of the kinetic and in situ spectroscopic data, a plausible surface-reaction mechanism is proposed for the vapor-phase LA hydrogenation to GVL in the presence of H₂O over the carbon-supported Ru catalyst.