Supported CoCl 2 catalyst for NaBH 4 dehydrogenation Çetin Çakanyıldırım * , Metin Gu ¨ ru ¨ Engineering and Architectural Faculty, Chemical Engineering Department, Gazi University, Maltepe, 06570 Ankara, Turkey article info Article history: Received 30 December 2008 Accepted 25 August 2009 Available online 31 October 2009 Keywords: NaBH 4 Catalyst CoCl 2 Hydrogen energy abstract In this paper, economically favorable, supported CoCl 2 catalysts were produced for NaBH 4 dehydroge- nation. Among the used supports, diatomite and g-Al 2 O 3 supports show great stability with CoCl 2 and do not break up during experiments some of which lasts 3000 min. Slow and continuous hydrogen release throughout all of the experiments is observed. Furthermore, prepared catalyst could be used for 250 h uninterruptedly. XRF and Atomic Absorption Spectrometer (AAS) analysis prove that CoCl 2 could be permanently joined and distributed homogeneously on the support surface. In addition, kinetic inves- tigations of the dehydrogenation reaction fit zero order kinetic for low temperatures while it obeys the first order at high temperature. Computation of activation energy results 132 kJ/mol for low and 78 kJ/ mol for high temperature regions. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The decreasing natural gas, coal and petroleum reserves, and increasing consumption rate of these resources force scientist to find alternative energy solutions. Hydrogen is a new energy carrier molecule for the future applications yet it has plenty of problems to be addressed before its effective utilization in trans- portation vehicles and small portable devices. Developing economic, clean and renewable energy systems can alleviate most of these problems. For this purpose, new hydrogen containing materials and some reaction systems are being investigated. NaBH 4 is an environment friendly option to store hydrogen. Thus, many current studies are investigating a way to find out a perfect hydrogen desorption method from NaBH 4 . This will also open a gate to feed the fuel cells with proton source to provide an uninterrupted energy supply. In summary, scientists are driven to discover new methods/materials to store hydrogen as well as catalysts to expedite the hydrogen desorption to support hydrogen- consuming fuel cells [1]. Sodium borohydride contains 10.8% hydrogen and stores it in solid form. Hydrogen can be taken from sodium borohydride by thermal decomposition or catalytic desorption. Theoretically, thermal decomposition yields only 10% (by weight) of the hydrogen in the storage medium, unfortunately this ratio is practically limited at 1%. In catalytic applications, it is possible to recover the most of the hydrogen from NaBH 4 [1]. In addition, catalytic approach is advantageous since the hydrogen in the surrounding water is also used [2,3]. 3D transition metals and their chlorides are often considered as best catalysts for dehydrogenation reactions due to their low cost and high activities [4–6]. On the other hand, well known catalyst such as Pt, Ru and Pd may be used when they are placed on suitable support materials [7–9]. Besides, a combination of these catalysts can be operated in dehydrogenation [10–12]. In catalytic studies deactiva- tion of active sites by the side-product NaBO 2 always reduces hydrogen yield. Concentration of NaBH 4 directly affects the NaBO 2 amount in the reactor. Studies suggest us to keep NaBH 4 concentra- tion at 5–25 wt% in the reaction environment [13,11]. Most of the researchers have reported that the 15 wt% NaBH 4 is the upper limit for an efficient reaction. Otherwise; sudden temperature rise because of an exothermic reaction, high viscosity or high NaBO 2 concentra- tion will adversely affect the efficiency of the process [10,11,5]. Generally, water is required to start the dehydrogenation. If the water amount is kept high, that is operating at a low NaBH 4 concentration, catalyst life may be longer per usage. It may be possible to install or achieve equilibrium in continuous flow operations between NaBH 4 concentration in bulk and NaBH 4 adsorbed on catalyst surface. g-Al 2 O 3 , silica and active carbon demonstrate good behaviors in an alkaline solution whose pH value is above 12 [7,4,13]. These materials have surface area changing from 80 to 1055 m 2 /g [13]. Surface area and pore diameter impress the reaction to be controlled by diffusion or kinetic. Preparation techniques or cata- lyst support type can cause the surface to exhibit different char- acteristics. Thus, the reaction order of the dehydrogenation needs to be described by various kinetic models, some of which include an adsorption phenomena [7,9,14]. * Corresponding author. Tel.: þ90 312 5823544; fax: þ90 312 2308434. E-mail address: cetinc@gazi.edu.tr (Ç. Çakanyıldırım). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2009.08.034 Renewable Energy 35 (2010) 839–844