Influence of the nature of support on Ru-supported catalysts for selective hydrogenation of citral J. Álvarez-Rodríguez a,b , I. Rodríguez-Ramos a , A. Guerrero-Ruiz b , E. Gallegos-Suarez a,b , A. Arcoya a,⇑ a Instituto de Catálisis y Petroleoquímica, CSIC, C/Marie Curie n° 2, Madrid 28049, Spain b Dpto. Química Inorgánica y Técnica, UNED, Senda del Rey n° 9, Madrid 28040, Spain highlights " Graphite, zirconia and KL as supports of Ru-catalysts for hydrogenation of citral. " Graphite promotes formation of Ru nÀ species and favors formation of geraniol and nerol. " Stabilization of Ru 0 AZr n+ species in Ru/zirconia activates the carbonyl group of citral. " Geometrical effects within Ru/KL enhance the selectivity toward unsaturated alcohols. " KL-zeolite improves formation of unsaturated alcohols more than graphite and zirconia. graphical abstract Ru/HSAG Ru/ZrO2 Ru/KL 0 20 40 60 80 100 Catalyst Citronellol Citronellal Geraniol + Nerol Citral conversion Conversion or Selectivity (%) article info Article history: Received 4 May 2012 Received in revised form 10 July 2012 Accepted 20 July 2012 Available online 31 July 2012 Keywords: Citral hydrogenation Unsaturated alcohols Ruthenium catalysts Metal-support interaction Decoration Confinement effect abstract Ruthenium catalysts supported on KL zeolite, ZrO 2 and graphite, prepared by incipient wetness impreg- nation, were characterized by N 2 adsorption, H 2 chemisorption, TEM and CO adsorption microcalorimetry and tested in the selective hydrogenation of citral in the liquid phase, at 5 MPa and 323 K. Characteriza- tion studies reveal that graphite promotes formation of electron-rich metal species (Ru nÀ ) that difficult hydrogenation of the conjugated C@C double bond of citral and indirectly favor the production of geraniol and nerol. For Ru/ZrO 2 catalyst, the Ru M ZrO 2 interaction at the interface, with formation of Ru 0 AZr n+ species as evidenced by the TEM and CO adsorption microcalorimetry measurements, activates the car- bonyl group of citral and enhances the selectivity towards unsaturated alcohols. Characterization mea- surements of Ru/KL evidence that metal nanoparticles placed inside of the zeolite channels block part of ruthenium loading and hinder the free transit of citral through the channels, thus reducing the overall hydrogenation activity of the catalyst. Furthermore, this steric hindrance impedes adsorption the conju- gated C@C double bond of citral and forces hydrogenation of the carbonyl group in terminal position. On the other hand, the fact that active sites on occluded particles are more resistant to poisoning than those easily accessible to citral enhances the selectivity towards geraniol and nerol, as the reaction time increases. The comparative analysis of the results indicates that, in order to increase the selectivity towards unsaturated alcohols, geometrical effects derived from the size, shape and location of ruthenium particles in the KL structure are more effective than the electronic modifications induced by graphite or zirconia on the ruthenium particles. Ó 2012 Elsevier B.V. All rights reserved. 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.07.099 ⇑ Corresponding author. Address: Instituto de Catálisis y Petroleoquímica, Marie Curie, n° 2 L10, 28049 Madrid, Spain. Fax: +34 915854760. E-mail address: aarcoya@icp.csic.es (A. Arcoya). Chemical Engineering Journal 204–206 (2012) 169–178 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej