《Hydrogenation of Citral over Ni and Ni-Sn Catalysts》.pdf

Turk J Chem 32 (2008) , 623 – 636. ¨ ˙ c TUBITAK Hydrogenation of Citral over Ni and Ni-Sn Catalysts Hilal AYKAC¸ , Selahattin YILMAZ∗ ˙ Izmir Institute of Technology, Chemical Engineering Department, ˙ G¨ulbah¸ce K¨oy¨u, Urla, Izmir-TURKEY e-mail: selahattinyilmaz@iyte.edu.tr Received 26.03.2007 Liquid phase citral hydrogenation over zeolite-supported monometallic Ni and bimetallic Ni-Sn cat- alysts was studied. The zeolite support materials were Na-Y, Na-mordenite, and clinoptilolite. Ni and Sn contents of the monometallic and bimetallic catalysts were 8.1-9.2 wt% and 0.46 wt%, respectively. The type of the zeolite support affected the activity and selectivity of the catalysts differently. The main product of the citral hydrogenation reaction was citronellal, for both monometallic (84.5% yield) and bimetallic (44.5% yield) catalysts. The addition of promoter increased the selectivity to unsaturated alcohols (geraniol+nerol), i.e. it changed from 0.9% to 6.3% over mordenite and from 0.9% to 2.1% over Na-Y-supported catalysts. Furthermore, activity of the Ni catalysts decreased while the quantity of acetal remained almost constant. Intimate contact between active metal, promoter, and support, and a catalyst with a high concentration of weak acid sites gave high selectivity to geraniol+nerol. Key Words: Citral, hydrogenation, citronellol, Ni, Ni-Sn, zeolite. Introduction Selective hydrogenation of α − β unsaturated aldehydes is a difficult challenge in the or