Surface changes in Ru/KL supported catalysts induced by the preparation method and their effect on the selective hydrogenation of citral

Several 2 wt.% Ru/KL supported catalysts were prepared by various methods with different ruthenium precursors and characterized by CO and H2 chemisorption, N2 adsorption, TPD of NH3, TEM and XPS. Furthermore, CO chemisorbed species have been studied by FT-IR and microcalorimetry. Characterization measurements of catalyst IWI-Ru, prepared by incipient wetness impregnation from ruthenium acetylacetonate, evidence metal nanoparticles of 1 nm placed inside the zeolite channels, thus blocking the accessibility to part of ruthenium loading inside the micropores. Catalyst prepared by treating the KL zeolite with RuCl3·xH2O aqueous solution (I-Ru) exhibits nanoparticles in the range 6–8 nm at the external surface and clusters smaller that 1 nm, inside the micropores. These latter do not significantly affect the diffusion of probe molecules through the channels. Catalytic performances in the selective hydrogenation of citral in the liquid phase, at 323 K and 5 MPa, show that IWI-Ru is less active than I-Ru, but more selective towards unsaturated alcohols. Furthermore, for IWI-Ru, selectivity increases with the increasing conversion. On the other hand, removal of acid sites of the I-Ru catalyst enhances the hydrogenation activity and increases the selectivity towards citronellal. All these results are analyzed and discussed in terms of the size, shape and location of ruthenium particles in the catalysts, as well as of the metal–support interaction.

Steric hindrances produced by metal nanoparticles of adequate size and shape inside the Ru/KL catalyst, prepared by incipient wetness impregnation (IWI-Ru), inhibit its activity in the hydrogenation of citral in the liquid phase, but enhance its selectivity towards unsaturated alcohols (G + N). This effect is not observed for Ru/KL catalysts prepared by other procedures.Figure optionsDownload as PowerPoint slide