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Title: Theoretical Investigations on the Formation and Dehydrogenation Reaction Pathways of H(NH2BH2)nH (n=1-4) Oligomers: Importance of Dihydrogen Interactions (DHI)

Abstract

The H(NH2BH2)nH oligomers are possible products from dehydrogenation of ammonia borane (NH3BH3) and ammonium borohydride (NH4BH4), which belong to a class of boron-nitrogen-hydrogen (BNHx) compounds that are promising materials for chemical hydrogen storage. Understanding the kinetics and reaction pathways of formation of these oligomers and their further dehydrogenation is essential for developing BNHx-based hydrogen storage materials. We have performed computational modeling using density functional theory (DFT), ab initio wavefunction theory, and Car-Parrinello molecular dynamics (CPMD) simulations on the energetics and formation pathways for the H(NH2BH2)nH (n=1-4) oligomers, polyaminoborane (PAB), from NH3BH3 monomers and the subsequent dehydrogenation steps to form polyiminoborane (PIB). Through transition state searches and evaluation of the intrinsic reaction coordinates, we have investigated the B-N bond cleavage, the reactions of NH3BH3 molecule with intermediates, dihydrogen release through intra- and intermolecular hydrogen transfer, dehydrocoupling/cyclization of the oligomers, and the dimerization of NH3BH3 molecules. We discovered the formation mechanism of H(NH2BH2)n+1H oligomers through reactions of the H(NH2BH2)nH oligomers first with BH3 followed by reactions with NH3 and the release of H2, where the BH3 and NH3 intermediates are formed through dissociation of NH3BH3. We also found that the dimerization of the NH3BH3 molecules to form c-(NH2BH2)2 is slightly exothermic, withmore » an unexpected transition state that leads to the simultaneous release of two H2 molecules. The dehydrogenations of the oligomers are also exothermic, typically by less than 10 kcal/(mol of H2), with the largest exothermicity for n=3. The transition state search shows that the one-step direct dehydrocoupling cyclization of the oligomers is not a favored pathway because of high activation barriers. The dihydrogen bonding, in which protic (HN) hydrogens interact with hydridic (HB) hydrogens, plays a vital role in stabilizing different structures of the reactants, transition states, and products. The dihydrogen interaction (DHI) within the -BH2(η2-H2) moiety accounts for both the formation mechanisms of the oligomers and for the dehydrogenation of ammonia borane. Support was provided from the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences Division and from the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Chemical Hydrogen Storage Center of Excellence. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
990533
Report Number(s):
PNNL-SA-71128
Journal ID: ISSN 0020-1669; INOCAJ; 25661; EB4202000; KC0302010; TRN: US201020%%393
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Inorganic Chemistry, 49(17):7710-7720
Additional Journal Information:
Journal Volume: 49; Journal Issue: 17; Journal ID: ISSN 0020-1669
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; AMMONIA; BONDING; BORANES; BOROHYDRIDES; CLEAVAGE; CYCLIZATION; DEHYDROGENATION; DIMERIZATION; DISSOCIATION; EVALUATION; FUNCTIONALS; HYDROGEN STORAGE; HYDROGEN TRANSFER; KINETICS; MONOMERS; SIMULATION; Environmental Molecular Sciences Laboratory

Citation Formats

Li, Jun, Kathmann, Shawn M, Hu, Han-Shi, Schenter, Gregory K, Autrey, Thomas, and Gutowski, Maciej S. Theoretical Investigations on the Formation and Dehydrogenation Reaction Pathways of H(NH2BH2)nH (n=1-4) Oligomers: Importance of Dihydrogen Interactions (DHI). United States: N. p., 2010. Web. doi:10.1021/ic100418a.
Li, Jun, Kathmann, Shawn M, Hu, Han-Shi, Schenter, Gregory K, Autrey, Thomas, & Gutowski, Maciej S. Theoretical Investigations on the Formation and Dehydrogenation Reaction Pathways of H(NH2BH2)nH (n=1-4) Oligomers: Importance of Dihydrogen Interactions (DHI). United States. doi:10.1021/ic100418a.
Li, Jun, Kathmann, Shawn M, Hu, Han-Shi, Schenter, Gregory K, Autrey, Thomas, and Gutowski, Maciej S. Mon . "Theoretical Investigations on the Formation and Dehydrogenation Reaction Pathways of H(NH2BH2)nH (n=1-4) Oligomers: Importance of Dihydrogen Interactions (DHI)". United States. doi:10.1021/ic100418a.
@article{osti_990533,
title = {Theoretical Investigations on the Formation and Dehydrogenation Reaction Pathways of H(NH2BH2)nH (n=1-4) Oligomers: Importance of Dihydrogen Interactions (DHI)},
author = {Li, Jun and Kathmann, Shawn M and Hu, Han-Shi and Schenter, Gregory K and Autrey, Thomas and Gutowski, Maciej S},
abstractNote = {The H(NH2BH2)nH oligomers are possible products from dehydrogenation of ammonia borane (NH3BH3) and ammonium borohydride (NH4BH4), which belong to a class of boron-nitrogen-hydrogen (BNHx) compounds that are promising materials for chemical hydrogen storage. Understanding the kinetics and reaction pathways of formation of these oligomers and their further dehydrogenation is essential for developing BNHx-based hydrogen storage materials. We have performed computational modeling using density functional theory (DFT), ab initio wavefunction theory, and Car-Parrinello molecular dynamics (CPMD) simulations on the energetics and formation pathways for the H(NH2BH2)nH (n=1-4) oligomers, polyaminoborane (PAB), from NH3BH3 monomers and the subsequent dehydrogenation steps to form polyiminoborane (PIB). Through transition state searches and evaluation of the intrinsic reaction coordinates, we have investigated the B-N bond cleavage, the reactions of NH3BH3 molecule with intermediates, dihydrogen release through intra- and intermolecular hydrogen transfer, dehydrocoupling/cyclization of the oligomers, and the dimerization of NH3BH3 molecules. We discovered the formation mechanism of H(NH2BH2)n+1H oligomers through reactions of the H(NH2BH2)nH oligomers first with BH3 followed by reactions with NH3 and the release of H2, where the BH3 and NH3 intermediates are formed through dissociation of NH3BH3. We also found that the dimerization of the NH3BH3 molecules to form c-(NH2BH2)2 is slightly exothermic, with an unexpected transition state that leads to the simultaneous release of two H2 molecules. The dehydrogenations of the oligomers are also exothermic, typically by less than 10 kcal/(mol of H2), with the largest exothermicity for n=3. The transition state search shows that the one-step direct dehydrocoupling cyclization of the oligomers is not a favored pathway because of high activation barriers. The dihydrogen bonding, in which protic (HN) hydrogens interact with hydridic (HB) hydrogens, plays a vital role in stabilizing different structures of the reactants, transition states, and products. The dihydrogen interaction (DHI) within the -BH2(η2-H2) moiety accounts for both the formation mechanisms of the oligomers and for the dehydrogenation of ammonia borane. Support was provided from the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences Division and from the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Chemical Hydrogen Storage Center of Excellence. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.},
doi = {10.1021/ic100418a},
journal = {Inorganic Chemistry, 49(17):7710-7720},
issn = {0020-1669},
number = 17,
volume = 49,
place = {United States},
year = {2010},
month = {9}
}