Determination of structure and phase transition of light element nanocomposites in mesoporous silica: case study of NH3BH3 in MCM-41

Journal Article · Wed Sep 30 04:00:00 EDT 2009 · Journal of the American Chemical Society, 131(38):13749-13755

DOI:https://doi.org/10.1021/ja904901d· OSTI ID:973718

Kim, Hyun Jeong; Karkamkar, Abhijeet J; Autrey, Thomas; Chupas, Peter; Proffen, Thomas E

The structure of ammonia borane (AB), NH3BH3, infused in mesoporous silica MCM-41 and its evolution over the temperature range of 80 to 300 K was investigated using the atomic pair distribution function (PDF) analysis of synchrotron X-ray powder diffraction data in order to understand the origin of improved dehydrogenation properties of the system. Our study shows how X-ray PDF analysis can be used to elucidate the structure of light guest species loaded in mesoporous silica materials despite of its low scattering power of composed elements (N, B, and H) compared to its host (SiO2). PDF analyses of two AB-loaded compositions with weight ratio AB:MCM-41=1:1 and 3:1 provide a strong evidence that AB aggregate, previously found in AB:MCM-41≥1:1 samples, is same species as neat AB. For both of them an orthorhombic to tetragonal structural phase transition occurs at 225 K on warming. On the other hand, AB residing inside meso-pores, which is found in AB:MCM-41=1:2 sample, does not undergo such phase transition. It rather stays in tetragonal phase over a wide temperature range of 110 to 240 K and starts to lose structural correlation above 240 K. This strongly suggests that nano-confinement of AB inside meso-pores stabilizes high temperature tetragonal phase at much lower temperature. These results provide important clues to two critical questions: why nan-compositions of AB leads dehydrogenation to lower temperature and why the neat AB like propoerties are recovered at high AB loading samples. This work was supported by the US Department of Energy Office of Basic Energy Sciences, Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 973718
• Report Number(s): PNNL-SA-67171; KC0302010
• Journal Information: Journal of the American Chemical Society, 131(38):13749-13755, Journal Name: Journal of the American Chemical Society, 131(38):13749-13755 Journal Issue: 38 Vol. 131; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
AMMONIA
BORANES
DEHYDROGENATION
DIFFRACTION
DISTRIBUTION FUNCTIONS
ORIGIN
SCATTERING
SILICA
SYNCHROTRONS