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Roles of Catalysts on Hydrogen Desorption of Mixtures of LiBH4 and MgH2 and Its Reversibility

Pattaraporn Sridechprasat1, Yindee Suttisawat1, Pramoch Rangsunvigit1, Boonyarach Kitiyanan1, and Santi Kulprathipanja2. (1) Petrochemical Technology, The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, 10330, Thailand, (2) UOP LLC, 50 East Algonquin Road, Des Plaines, IL 60017-5016

Effects of catalysts (Ti, TiO2, and TiCl3) on hydrogen desorption of a 2:1 molar ratio of LiBH4:MgH2 and its reversibility were investigated. 3 mol% of a Ti-compound were added as a catalyst in the hydride mixture using mechanical ball-milling for one hour as a mixing means. Hydrogen desorption was carried out under atmospheric pressure with the temperature range from 25 to 500C and a heating rate of 2C min-1 while hydrogen re-absorption took place at 5 MPa hydrogen pressure and 350C. The hydrogen desorption results of the uncatalyzed (LiBH4-MgH2) and catalyzed mixtures occurred in two steps. It was found that the uncatalyzed and catalyzed mixtures started to release hydrogen at the same temperature of 150C for the first step and 400C for the second step. In the presence of a catalyst, the mixtures released hydrogen at a higher amount (6.5 wt%) than that of LiBH4-MgH2 (3 wt%) in the first step. When the temperature reached 500C, the hydrogen desorption of both mixtures were approximately the same, 7 wt%. To understand roles of the metal hydrides and the catalysts in each step of the hydrogen desorption, all mixtures were characterized by XRD. The results identified that the hydrogen desorption from the first step was contributed by a reaction between LiBH4 and MgH2 while that from the second step was from a reaction between LiBH4 and Mg. Furthermore, the catalysts affected the decomposition of MgH2 in a greater extent than LiBH4. Both LiBH4-MgH2 and that with any tested catalyst possessed better reversibility than each hydride alone. In addition, the hydrogen desorption and re-absorption using difference types of the catalysts will also be discussed.