Journal of Catalysis 253 (2008) 111–118 www.elsevier.com/locate/jcat New aspects for heterogeneous cobalt-catalyzed hydroamination of ethanol A.K. Rausch a , E. van Steen b , F. Roessner a,∗ a Industrial Chemistry 2, University of Oldenburg, 26111 Oldenburg, Germany b Catalysis Research Centre, Department of Chemical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa Received 4 May 2007; revised 6 October 2007; accepted 21 October 2007 Available online 26 November 2007 Abstract Gas-phase hydroamination of ethanol and ammonia over supported cobalt on silica catalysts was investigated at 103 kPa. Besides the desired products, mono-, di- and triethylamine, acetonitrile, diethylimine, and hydrocarbons (methane, ethene, ethane, propane, and propene) were iden- tified as byproducts. The formation of hydrocarbons was found to depend on the cobalt loading of the catalyst and on the pretreatment of the catalyst. Guaranteeing a sufficient reduction of the cobalt catalyst allows a reduction in the selectivity of hydrocarbons from 25 to 10 mol% at a constant conversion of 90%. In addition, rapid deactivation of the catalyst was observed in the absence of hydrogen. The deactivation was ascribed to the interaction of ammonia with the catalyst and is largely reversible. Carbonaceous species are present on the spent catalyst, as shown by temperature-programmed reduction. These species are thought to be responsible for a slow deactivation in the presence of hydrogen.  2007 Elsevier Inc. All rights reserved. Keywords: Ethanol amination; Cobalt; Catalyst deactivation 1. Introduction Short-chain aliphatic amines (C 2 –C 6 ) are important inter- mediates for the chemical and pharmaceutical industries. Nu- merous drugs, dyes, herbicides, and other compounds contain amino groups that are introduced by reaction with an amine [1]. The production of aliphatic amines is often performed by hy- droamination, the conversion of an alcohol with ammonia or a primary or secondary amine in the presence of hydrogen. A typical heterogeneous catalyst for hydroamination contains metallic cobalt, nickel or copper supported on silica or alumina. The conversion of alcohol is believed to be metal-catalyzed, with activity for the conversion of the alcohol proportional to the metal surface area [2]. Due to the manifold applications of amines, hydroamination has been investigated using a variety of alcohols and amines or ammonia [3]. The hydroamination of ethanol with ammo- nia, the topic of the present study, was investigated by Sewell et al. [4] on cobalt catalysts and by Jones et al. [5] and Jackson et al. [6] on nickel catalysts. The results reported to date have * Corresponding author. Fax: +49 0441 798 3360. E-mail address: frank.roessner@uni-oldenburg.de (F. Roessner). not demonstrated a single consistent mechanism, because they were achieved for a range of catalysts and educts under different reaction conditions. Two mechanisms are primarily discussed for the hydroamination of ethanol [3,5–7], both of which as- sume that the abstraction of the α-H-atom of the alcohol is the rate-determining step in amination. These mechanisms differ with respect to the nitrogen-containing intermediates adsorbed on the catalysts surface. Baiker et al. [7] investigated the ki- netics of the amination of long-chain aliphatic alcohols with methylamines and proposed a reaction pathway with nitrogen- containing intermediates with a hydroxyl group (see Scheme 1). The intermediate amino alcohol is converted through elimina- tion of the hydroxyl group and subsequent addition of hydrogen to amines. Jones et al. [5] and Jackson et al. [6] proposed a mechanism for the amination of ethanol with ammonia based on their experiments with nickel catalysts suggesting the for- mation of surface ethylidene [5] or ethyl [6] intermediates. The C–N bond is formed in a reaction between the chemisorbed amine or ammonia and an oxygen-free surface derivative of the alcohol (see Scheme 2). This mechanism yielded a better de- scription for hydroamination of isotopic-labeled ethanol with ammonia. However, DFT calculations performed by Cheng et al. [8] showed that the mechanism proposed by Baiker et al. [7] 0021-9517/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2007.10.013