Gas phase hydrogenation of ortho-chloronitrobenzene (O-CNB) to ortho-chloroaniline (O-CAN) over unpromoted and alkali metal promoted-alumina supported palladium catalysts Venkataraman Vishwanathan a, * , Venkatreddy Jayasri a , P. Mahaboob Basha a , Nagendranath Mahata a , Lucky Sikhwivhilu b , Neil J. Coville b, * a Catalysis and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500007, India b Molecular Sciences Institute and School of Chemistry, University of the Witwatersrand, Johannesburg WITS 2050, South Africa Received 4 April 2007; received in revised form 11 July 2007; accepted 11 July 2007 Available online 28 July 2007 Abstract A series of alkali metals (Li, Na, K and Cs) promoted alumina-supported palladium catalysts were prepared by a wet impregnation method and characterized by X-ray diffraction (XRD) and CO chemisorption measurements. The samples were tested for the gas phase hydrogenation of ortho-chloronitrobenzene (O-CNB) to ortho-chloroaniline (O-CAN) in a fixed-bed micro reactor at 250 °C under nor- mal atmospheric pressure. The promoted-Pd/Al 2 O 3 catalysts show higher conversion for O-CNB and the hydrogenation activity of O- CNB per site decreases with the increasing ionic radius of the alkali metal promoter ions. However, the selectivity for O-CAN remains more or less the same in both unpromoted and promoted catalysts and also irrespective of the nature of the alkali metal promoter ions used for promotion of alumina support. Despite, similar activity and selectivity observed between Li- and Na-promoted Pd/Al 2 O 3 cat- alysts, the Na-promoted showed higher resistance for coke formation than a Li-promoted catalyst. The increase in the intrinsic activity of palladium site on alkali promotion has been attributed to the increase in hydrogenation activity over promoted catalysts. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Hydrogenation; Alkali-promotion; Deactivation; Intrinsic activity 1. Introduction Aromatic chloroamines are industrially important in the production of dyes, herbicides, drugs and pesticides. These compounds are synthesized from the corresponding chloro- nitroaromatics either using metal–acid systems or by cata- lytic hydrogenation over a supported metal catalyst. Due to the stringent environmental regulations, the latter route is a preferred one. It is known that catalytic hydrogenation promotes hydrodehalogenation to some extent, if right choices of catalysts are not used in the reaction medium. Hence, designing a suitable supported metal catalyst sys- tem for the title reaction is an important proposition. Several types of supported metal catalysts have been used with varying degrees of success for the synthesis of CAN from CNB [1–12]. Most of them show good selectiv- ity for chloroanilines but their hydrogenation activities remain low. Among supported metal catalysts, noble metal-based catalysts, are primarily used in most of the chemical industries. Ru, Rh and Ir are more selective for this reaction [8–11] but their catalytic activities are lower. Pt is very expensive. Supported Pd catalysts, though show better activity, the selectivity for chloroaniline remains lower because of a serious dehalogenation reaction [8,12]. Apart from the metal component of the catalyst, the sup- port of the catalyst too plays an important role. MgO- based supported catalysts, although they show better 1566-7367/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2007.07.018 * Corresponding authors. E-mail addresses: vvnathan2004@yahoo.co.in (V. Vishwanathan), ncoville@aurum.chem.wits.ac.za (N.J. Coville). www.elsevier.com/locate/catcom Available online at www.sciencedirect.com Catalysis Communications 9 (2008) 453–458