Rotational dynamics in ammonia borane: Evidence of strong isotope effects

Cantelli, R.; Paolone, A.; Palumbo, O.; Leardini, Fabrice; Autrey, Tom; Karkamkar, Abhijeet J.; Luedtke, Avery T.

doi:10.1016/j.jallcom.2013.03.148

Cited by 6 publications

(4 citation statements)

References 24 publications

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“…Furthermore, the isotope in situ mass spectrometry was applied to determine the source of hydrogen using deuterated water (D 2 O). Of course, it must be mentioned that H–D exchanges between D 2 O and [−NH 3 ] in AB easily occur in the D 2 O and then to form the [−ND 3 ] group. ,− However, since the H or D on the [−ND 3 ] group does not participate in the hydrolysis, which makes it not contribute to the production of hydrogen. At the same time, the solvent contains only a small amount of H 2 O after H–D exchange.…”

Section: Resultsmentioning

confidence: 99%

Visible-Light-Driven Multichannel Regulation of Local Electron Density to Accelerate Activation of O–H and B–H Bonds for Ammonia Borane Hydrolysis

Zhang

Liu

et al. 2020

ACS Catal.

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Regulating electron density at the active site by integrating contributions from multiple channels is an effective strategy to accelerate the reaction rate. Herein, the hydrolysis of ammonia borane (AB) is systematically studied on the NiCu alloy-loaded carbon nitride nanosheets (Ni x Cu y /CNS). The TOF of AB hydrolysis for NiCu/CNS catalyst under visible light irradiation was nearly 3.5 times higher than that in the dark. Photoelectrochemical characterizations indicate that the improved photocatalytic activities originate from a combination of alloying effect, Mott–Schottky junction at the metal–semiconductor interface as well as the localized surface plasmon resonance induced under the visible light irradiation, which synergistically increase the local electron density at the active Ni sites. More importantly, the infrared spectra and isotope labeling-mass spectrometry methods were used to establish the source of hydrogen and unravel the reaction mechanism. It is suggested that the cleavages of B–H and O–H bonds are the initial steps of AB hydrolysis, which lead to the formation of intermediates M–H– (metal and electronegative H– from −BH3) and M–H+ (metal and electropositive H+ from H2O), respectively. The H2 molecule could form through three main paths as (1) two H atoms from −BH3, (2) two H atoms from H2O, and (3) one H atom from −BH3 and another from H2O. Results of density functional theory (DFT) calculations are consistent with the formation of electron-rich Ni sites in the NiCu, and the activation of H2O is a rate-limiting step (RLS). Redistribution of electrons in NiCu significantly enhances the adsorption of AB, the activation of H2O molecules, and the associative desorption of H adatoms as well, which effectively promote the cleavage of B–H and O–H bonds and release of H2. This work gives a systematic mechanistic study on photocatalytic AB hydrolysis involving multichannel electron-transfer pathways, which will provide a powerful guidance for the rational design of active catalysts for AB hydrolysis through multipronged effects.

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Section: Resultsmentioning

confidence: 99%

Visible-Light-Driven Multichannel Regulation of Local Electron Density to Accelerate Activation of O–H and B–H Bonds for Ammonia Borane Hydrolysis

Zhang

Liu

et al. 2020

ACS Catal.

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“…ND 3 BH 3 was synthesized by repeating dissolution of AB in D 2 O and evaporation under vacuum at room temperature three times. 34 Ca(NH 2 ) 2 was prepared by the reaction of Ca powder and liquid NH 3 (R2). Ca(NH 2 BH 3 ) 2 was made by dissolving the mixture of NH 3 BH 3 and Ca(NH 2 ) 2 in THF according to R3.…”

Section: Sample Preparationmentioning

confidence: 99%

Synthesis, structure and the dehydrogenation mechanism of calcium amidoborane hydrazinates

Zhao

et al. 2016

Phys. Chem. Chem. Phys.

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The calcium amidoborane hydrazinates, Ca(NH2BH3)2·nN2H4, were firstly synthesized by reacting different molar ratios of Ca(NH2BH3)2 and N2H4. In particular, Ca(NH2BH3)2 and N2H4 with a molar ratio of 1 : 2 crystallizes into the orthorhombic symmetry P212121 space group with the lattice parameters of a = 6.6239(4) Å, b = 13.7932(6) Å, c = 4.7909(2) Å. The dehydrogenations of calcium amidoborane hydrazinates are two-step reactions, exhibiting superior dehydrogenation properties compared with those of pristine Ca(NH2BH3)2. For Ca(NH2BH3)2-1/2N2H4, approximately 4.6 equiv. hydrogen (or 7.9 wt% hydrogen) can be released at 150 °C. Kinetic analysis shows that the activation energies for the two steps of hydrogen desorption from Ca(NH2BH3)2·2N2H4 are much lower than those of pristine Ca(NH2BH3)2, suggesting an improvement in the dehydrogenation kinetics of Ca(NH2BH3)2 after coordinating with N2H4. Isotopic labeling results show that the driving force for the dehydrogenation of calcium amidoborane hydrazinates is the combination mechanism of protonic hydrogen and hydridic hydrogen (H(δ+) and H(δ-)). In addition, initial H2 release from calcium amidoborane hydrazinates originates from the interaction of [-BH3] and N2H4, rather than [-BH3] and [-NH2] (in [-NH2BH3]).

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“…For condensed phase and clusters, each hydridic end (BH) of ammonia a) Author to whom correspondence should be addressed. Electronic mail: erb@Colostate.edu borane acts as a hydrogen acceptor for the protic end (NH) of an adjacent molecule: 13,25 the B-N bond between the donor atom and the acceptor atom is considerably shorter in the crystal than it is in a gas phase cluster. 15,18,23,24 The general trend is that shorter bonds are found in larger conglomerates.…”

Section: Introductionmentioning

confidence: 99%

Dynamics and fragmentation of van der Waals and hydrogen bonded cluster cations: (NH3)n and (NH3BH3)n ionized at 10.51 eV

Yuan

Shin

Bernstein

2016

The Journal of Chemical Physics

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A 118 nm laser is employed as a high energy, single photon (10.51 eV/photon) source for study of the dynamics and fragmentation of the ammonia borane (NH3BH3) cation and its cluster ions through time of flight mass spectrometry. The behavior of ammonia ion and its cluster ions is also investigated under identical conditions in order to explicate the ammonia borane results. Charge distributions, molecular orbitals, and spin densities for (NH3BH3)n and its cations are explored at both the second-order perturbation theory (MP2) and complete active space self-consistent field (CASSCF) theory levels. Initial dissociation mechanisms and potential energy surfaces for ionized NH3BH3, NH3, and their clusters are calculated at the MP2/6-311++G(d,p) level. Protonated clusters (NH3)xH(+) dominate ammonia cluster mass spectra: our calculations show that formation of (NH3)n-1H(+) and NH2 from the nascent (NH3)n(+) has the lowest energy barrier for the system. The only common features for the (NH3)n(+) and (NH3BH3)n(+) mass spectra under these conditions are found to be NHy(+) (y = 0,…,4) at m/z = 14-18. Molecular ions with both (11)B and (10)B isotopes are observed, and therefore, product ions observed for the (NH3BH3)n cluster system derive from (NH3BH3)n clusters themselves, not from the NH3 moiety of NH3BH3 alone. NH3BH2(+) is the most abundant ionization product in the (NH3BH3)n(+) cluster spectra: calculations support that for NH3BH3(+), an H atom is lost from the BH3 moiety with an energy barrier of 0.67 eV. For (NH3BH3)2(+) and (NH3BH3)3(+) clusters, a B(δ+)⋯H(δ-)⋯(δ-)H⋯(δ+)B bond can form in the respective cluster ions, generating a lower energy, more stable ion structure. The first step in the (NH3BH3)n(+) (n = 2, 3) dissociation is the breaking of the B(δ+)⋯H(δ-)⋯(δ-)H⋯(δ+)B moiety, leading to the subsequent release of H2 from the latter cluster ion. The overall reaction mechanisms calculated are best represented and understood employing a CASSCF natural bond orbital description of the valence electron distribution for the various clusters and monomers. Comparison of the present results with those found for solid NH3BH3 suggests that NH3BH3 can be a good hydrogen storage material.

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Rotational dynamics in ammonia borane: Evidence of strong isotope effects

Cited by 6 publications

References 24 publications

Visible-Light-Driven Multichannel Regulation of Local Electron Density to Accelerate Activation of O–H and B–H Bonds for Ammonia Borane Hydrolysis

Visible-Light-Driven Multichannel Regulation of Local Electron Density to Accelerate Activation of O–H and B–H Bonds for Ammonia Borane Hydrolysis

Synthesis, structure and the dehydrogenation mechanism of calcium amidoborane hydrazinates

Dynamics and fragmentation of van der Waals and hydrogen bonded cluster cations: (NH3)n and (NH3BH3)n ionized at 10.51 eV

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