Selective Hydrogenation of Citral Over Noble Metals Intercalated Montmorillonite Catalysts
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Selective Hydrogenation of Citral Over Noble Metals Intercalated Montmorillonite Catalysts D. Manikandan Æ D. Divakar Æ T. Sivakumar
Received: 4 December 2007 / Accepted: 9 January 2008 / Published online: 5 February 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Surfactant stabilized platinum and ruthenium nano particles were intercalated into the interlamellar space of montmorillonite. The XRD patterns of the metal intercalated montmorillonite reveal that there was a significant swelling during the intercalation of surfactant stabilized metal particles without affecting the crystallinity of montmorillonite. The success of the synthesis of nano particles into montmorillonite catalysts was confirmed from the TEM micrographs of the catalytic materials. The TEM micrographs clearly indicated well dispersion of particles and the average diameter (in nm) of the intercalated metal particles were also determined. The catalytic activity and selectivity of these newly developed catalysts towards the selective hydrogenation of citral in liquid phase was found to be appreciable. The conversion levels were found to be 38% and 18% at 30 °C and increased to 61% and 46% at 100 °C over Pt-CTA-MM 2 and Ru-CTAMM 2 catalysts respectively at 9 bar hydrogen pressure. The best selectivity towards geraniol and nerol was observed to be 61% over Pt-CTA-MM 2 among the catalysts studied. The effect of temperature, hydrogen pressure, amount of catalyst and time on stream on the conversion and selectivity towards geraniol and nerol were also discussed in detail. Keywords Noble metal catalysts Intercalation Selective hydrogenation Citral
D. Manikandan D. Divakar T. Sivakumar (&) Catalysis Laboratory, Department of Chemical Engineering, A.C. College of Technology, Anna University, Chennai 600 025, India e-mail: [email protected]
1 Introduction Selective catalytic hydrogenation of a, b-unsaturated aldehydes is an important step in the preparation of various fine chemicals. The products unsaturated alcohols are important intermediates in several industries such as flavour, fragrance and pharmaceutical industries [1–3]. Crotonaldehyde and cinnamaldehyde are the most widely documented compounds in this respect [4–13]. However, among the unsaturated carbonyl compounds, citral is particularly attractive, because it possesses an isolated C=C bond in addition to the conjugated C=O and C=C bonds [14–20]. Thus obtaining the selective products by overcoming the C=C hydrogenation and the possible isomerisation with another C=C has been a difficult task for decades. Since the reaction pathway is complicated, understanding the properties of the catalysts in the selective hydrogenation of citral is still difficult. As citral exists in two different isomeric forms namely E and Z forms, the hydrogenation may take place through various pathways resulting in different products such as geraniol and nerol, citronellal or 3, 7-dimethyloctanol as shown in Fig. 1. Apart from these reactions, secondary processes of cyclization or of reaction
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