Preparation of a new Ti catalyst for improved performance of NaAlH4

Abstract

Three effective Ti catalysts for NaAlH4 were made by stoichiometrically reacting TiCl3 with LiAlH4 in tetrahydrofuran (THF), NaAlH4 in THF, and LiAlH4 in diethyl ether (Et2O). 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. NaAlH4 was dry doped with 2 mol% of these ex situ catalysts, and for comparison, NaAlH4 was conventionally wet doped with 2 mol% TiCl3 in THF that made in situ catalyst (designated as TiCl3). 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 > TiCl3 > 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 NaAlH4 catalysts to date, such as CeCl3, ScCl3 and Ti nanocluster. It is easy to make, readily available and relatively inexpensive.