Kim, Yoonyoung and Hwang, Son-Jong and Lee, Young-Su and Suh, Jin-Yoo and Han, Heung Nam and Cho, Young Whan (2012) Hydrogen Back-Pressure Effects on the Dehydrogenation Reactions of Ca(BH_4)_2. Journal of Physical Chemistry C, 116 (49). pp. 25715-25720. ISSN 1932-7447 http://resolver.caltech.edu/CaltechAUTHORS:20130118-095005279
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The dehydrogenation reactions of Ca(BH_4)_2 are investigated under different isobaric conditions using in situ synchrotron radiation powder X-ray diffraction and nuclear magnetic resonance measurements. Ca(BH_4)_2 dissociates in multiple steps, and several intermediate phases, such as an amorphous phase(s), CaB_2Hx, and CaB_(12)H_(12), are observed during dehydrogenation. Among the intermediate phases, it is known that CaB_2Hx is fully reversible, while the more stable CaB_(12)H_(12) with an icosahedral structure hinders reversible reactions. Here, we try to control the dehydrogenation reaction pathway of Ca(BH_4)_2 by applying different hydrogen back-pressures. The decomposition reaction of Ca(BH_4)_2 in the absence of a catalyst was found to be sensitive to the H_2 back-pressure. At p(H_2) = 1 bar, Ca(BH_4)_2 decomposes via two competitive dehydrogenation reaction routes to form CaB_2H_x or CaB_(12)H_(12). At p(H_2) = 10 bar, the overall dehydrogenation reaction remains unchanged. However, the formation of CaB_2H_x is reduced, and amorphous elemental boron is observed as a final dehydrogenation product. At p(H_2) = 20 bar, the elemental boron formation is significantly increased, and the formation of the CaB_2H_x phase is suppressed. Possible routes to form CaH_2 and elemental boron are discussed.
|Additional Information:||© 2012 American Chemical Society. Received: September 10, 2012. Revised: November 19, 2012. Published: November 20, 2012. This work was sponsored by the Korea Research Council of Fundamental Science and Technology via a joint research project. We thank Drs. Keun Hwa Chae and Ik Jae Lee of PAL for the in situ synchrotron XRD measurements. The NMR facility at Caltech is supported by the National Science Foundation (NSF) under Grant No. 9724240 and partially supported by the MRSEC Program of the NSF under Award No. DMR-520565. H.N.H. and Y.K. acknowledge support by the Converging Research Center Program (Grant No. 2011K000599) through the Ministry of Education, Science and Technology of the Korean Government.|
|Official Citation:||Hydrogen Back-Pressure Effects on the Dehydrogenation Reactions of Ca(BH4)2 Yoonyoung Kim, Son-Jong Hwang, Young-Su Lee, Jin-Yoo Suh, Heung Nam Han, and Young Whan Cho The Journal of Physical Chemistry C 2012 116 (49), 25715-25720|
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|Deposited By:||Ruth Sustaita|
|Deposited On:||18 Jan 2013 19:20|
|Last Modified:||18 Jan 2013 19:20|
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