Characterization of Iridium Catalyst for Decomposition of Hydrazine Hydrate for Hydrogen Generation
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Catalysis Letters Vol. 109, Nos. 3–4, July 2006 ( 2006) DOI: 10.1007/s10562-006-0081-3
Characterization of iridium catalyst for decomposition of hydrazine hydrate for hydrogen generation Sung June Cho,a,* Jun Lee,a Yun Sung Lee,a and Dong Pyo Kimb a
Department of Applied Chemical Engineering and the Research Institute for Catalysis, Chonnam National University, Yong Bong 300, Buk-gu, Gwang-ju 500-757, Korea b Department of Fine Chemical Engineering & Chemistry, Polymer-derived Advanced Ceramic Materials Laboratory, Chungnam National University, 220 Kung-dong, Yuseong-gu, Daejon 305-764, Korea
Received 31 January 2006; accepted 23 March 2006
A catalyst with an ultra high iridium load was prepared using a method involving multiple impregnations. The obtained iridium catalyst contained between 29 and 35 wt% of 2 nm-sized nanoparticles dispersed on a support such as reinforced alumina, bauxite and precipitated alumina. XAFS suggested a possible structural model of Ir4 surrounded by oxygen. The decomposition of hydrazine hydrate to its elements was used as a probe reaction. The results showed that a catalyst support with a high mechanical strength such as reinforced alumina and bauxite is essential for sustaining the decomposition reaction of hydrazine hydrate where there is a high degree of mechanical and thermal shock. The decomposition reaction of hydrazine monohydrate (N2H4 Æ H2O) proceeded rapidly to generate a COx-free hydrogen-rich gas through contact with the iridium catalyst at room temperature. KEY WORDS: iridium catalyst; hydrazine hydrate; hydrogen generation.
1. Introduction There has been considerable interest in hydrogen storage in addition to the transport technology for its utilization. Potential solutions using novel nanomaterials have been proposed and investigated extensively. Carbon adsorption using carbon nanotubes or modified carbon materials, metal borohydride technology based on the coupled recycling of NaBH4–NaBO2 and the Mg–MgO reaction etc. are promising technologies. However, many problems need to be overcome before they can be commercialized such as a high storage quantity, cost-effectiveness, etc. [1]. The decomposition of ammonia using a catalyst has been examined as a means of supplying COx-free hydrogen, which requires a high reaction temperature (>573 K) to be converted into nitrogen and hydrogen [2]. Hydrazine, N2H4, as monopropellant was investigated for use in satellite propulsion using an Ir based catalyst [3]. Shell405TM (30 wt% Ir/Al2O3) was milestone in the development of such a catalyst, which activated anhydrous hydrazine even at 293 K [4]. Hydrazine can be converted in the following two ways: N2H4(g) fi N2(g)+2H2(g), DH=)95.4 kJ mol)1 and 3N2H4(g) fi 4NH3+N2(g),DH=)157 kJ mol)1 [5]. Thus, the hydrazine can be used as a hydrogen source because it contains 12.5 wt% H, surpassing the DOE (Department of Energy, USA) target of 6.5 wt% H [6]. However, anhydrous hydrazine, >98% is highly toxic *To whom correspondence should be addressed. E-mail: [email protected]
and explosive
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