Preparation of a new Ti catalyst for improved performance of NaAlH 4 Jun Wang, Armin D. Ebner, James A. Ritter* Department of Chemical Engineering, Swearingen Engineering Center, University of South Carolina, 301 Main Street, Columbia, SC 29208, USA article info Article history: Received 12 March 2012 Received in revised form 9 May 2012 Accepted 20 May 2012 Available online 19 June 2012 Keywords: Complex hydride Sodium aluminum hydride Lithium aluminum hydride Hydrogen storage abstract Three effective Ti catalysts for NaAlH 4 were made by stoichiometrically reacting TiCl 3 with LiAlH 4 in tetrahydrofuran (THF), NaAlH 4 in THF, and LiAlH 4 in diethyl ether (Et 2 O). The solid products produced after drying were named ex situ catalysts and designated respectively as Ti(Li)T, Ti(Na)T and Ti(Li)E. NaAlH 4 was dry doped with 2 mol% of these ex situ catalysts, and for comparison, NaAlH 4 was conventionally wet doped with 2 mol% TiCl 3 in THF that made in situ catalyst (designated as TiCl 3 ). All four doped samples were dry ball milled, and hydrogenation and dehydrogenation studies were carried out over five cycles. Temperature programmed desorption, constant temperature desorption, and constant temperature cycling curves showed that the effectiveness of these catalysts decreased as Ti(Li) T > Ti(Na)T > TiCl 3 > Ti(Li)E. Ti(Li)T ex situ catalyst, being the best Ti catalyst, markedly decreased the dehydrogenation temperature, improved both the hydrogenation and dehydrogenation kinetics with sustained rates over cycling, and exhibited the least loss of hydrogen storage capacity over cycling. Ti(Li)T ex situ catalyst exhibited properties commensurate with some of the best NaAlH 4 catalysts to date, such as CeCl 3 , ScCl 3 and Ti nanocluster. It is easy to make, readily available and relatively inexpensive. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Since the pioneering work of Bogdanovic and Schwickardi [1] over a decade ago, Ti-doped NaAlH 4 has been and still is being studied intensively, as noted in recent review articles [2e4]. There are two reasons for this continued and intense interest with this material. It still has potential as a reversible hydrogen storage material for numerous small scale power and stationary applications (but probably not automotive applications) [2]; and the research has and still is stimulating the development of similar materials with even higher hydrogen storage capacities [2,5e9]. The decomposition of NaAlH 4 proceeds in two steps according to Eqs. (1) and (2), and produces at most 5.6 wt% hydrogen as the theoretical upper limit. 3NaAlH 4 4Na 3 AlH 6 þ 2Al þ 3H 2 (1) 2Na 3 AlH 6 46NaH þ 2Al þ 3H 2 (2) The dehydrogenation and especially the hydrogenation performance are markedly improved by adding some form of Ti as a catalyst, such as Ti-butoxide [1,10], TiCl 3 [1,11] or Ti nanocluster [12,13]. Hence, considerable research and devel- opment has been done on learning how to dope NaAlH 4 with Ti and other catalysts. * Corresponding author. Tel.: þ1 803 777 3590; fax: þ1 803 777 8265. E-mail addresses: ritter@cec.sc.edu, ritter@engr.sc.edu (J.A. Ritter). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 11650 e11655 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.05.101