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Solutions for Chemical Hydrogen Storage: Hydrogenation/Dehydrogenation of B-N Bonds

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Solutions for Chemical Hydrogen Storage: Hydrogenation/Dehydrogenation of B-N Bonds Solutions for Chemical Hydrogen Storage: Hydrogenation/ Dehydrogenation of B-N Bonds PIs: Karen Goldberg and Mike Heinekey Co-workers: Tony St. John, Brandon Dietrich, Travis Hebden, Steve Matthews (partners in the Chemical Hydrogen Storage Center) Project ID # STP_17_Goldberg This presentation does not contain any proprietary, confidential, or otherwise restricted information 1 Overview Timeline Barriers • Start: FY 05 • System Weight and Volume • End: FY 09 • H2 Charging/Discharging Rate • 80% Complete • System Cost • Regeneration Processes Budget Partners • Total project funding • University of Oregon – $1.1 M DOE share – $0.28 M cost share • University of Alabama • Funding received in FY08 • Pacific Northwest National Laboratory (PNNL) – $246,820 • Los Alamos National • Funding for FY09 Laboratory (LANL) – $300,000 2 Objectives • Develop cost-effective metal catalysts for the dehydrogenation of BN hydrogen storage materials – Focus on cheap widely available non-platinum group metals such as cobalt and iron • Optimize catalysts to meet DOE target goals for H2 discharging rates from BN materials • Collaborate with the U of Oregon to develop systems based on novel CBN materials – Identify and investigate catalysts capable of dehydrogenating both B-N and C-C bonds – Investigate the potential of direct regeneration of spent CBN fuels 3 Approach t O O t [Ir]H2 = Bu Bu P Ir P tBu tBu H H Highly active Basic Tridentate catalyst Ligand Motif • Synthesis of new metal catalysts based on the tridentate ligand motif – Replace Ir with inexpensive metal – Tune L, L’, L’’ and X to achieve high activity and catalyst stability 4 Approach • Measure rates and extents of hydrogen release from BN and CBN materials • Investigate systems where spent fuel can potentially be regenerated – Identify CBN compounds that have favorable thermodynamics (collaboration with U of Alabama) – Screen catalysts with target CBN materials prepared by U of Oregon and investigate rehydrogenation of B-N and C-C bonds. avg. !H wt% H2 H (kcal/mol H2) Distinct from Air Products approach N N 6.4 7.1 • contains boron B N – 4 H2 B N • lower average ΔH H H H • one CC is replaced by BN NH NH • lower activation energy in some of the steps 2 7.1 7.7 BH BH • synergistically combines features of 2 – 3 H2 ammonia borane and cyclic systems H B NH HB NH 2 2 8.2 9.3 H N BH HN BH 2 2 – 3 H2 5 Key Accomplishments for 2008 • Collaborated with the University of Oregon on CBN materials – Transferred synthetic portion of effort to U of Oregon – Began screening CBN materials provided by U of Oregon for dehydrogenation activity with known AB dehydrogenation catalyst • Identified soluble products in models of liquid spent fuel: iridium catalyzed dehydrogenation of ammonia borane (AB) and methylamine borane (MeAB) mixtures – Identified soluble products as mixtures of oligomers of varying chain lengths – Observed cross-linked products in the mixed AB/MeAB containing both (NH2BH2) and (CH3NHBH2) units – Demonstration of an important capability for characterization of liquid spent fuels – Collaboration with LANL • Successfully extended highly active (POCOP)Ir motif to a first row metal (cobalt) • Optimized the previously reported cobalt pre-catalyst and targeted more robust ligand motifs 6 Identifying Soluble Products in Models of Liquid Spent Fuels [Ir]H2 n MeNH2BH3 [MeNHBH2]n n H2 THF, rt Soluble [Ir]H2 NH3BH3 MeNH2BH3 [NH2BH2]x[MeNHBH2]y 2 H2 THF, rt 1 : 1 Soluble 2 : 1 Solubles + “Pentamer” 5 : 1 Solubles + Even More “Pentamer” Soluble iridium-catalyzed dehydrogenation products of MeAB and mixtures of AB/MeAB can be identified using Electro- spray Ionization Mass Spectrometry (ESI-MS) techniques 7 Identifying Soluble Products • Soluble products are Actual ESI-MS Spectrum (selected region) mixtures of oligomers (CH3NHBH2)11 (CH3NHBH2)10 • Gel Permeation (CH3NHBH3)(CH3NHBH2)9(NH2CH3) Chromotography (GPC) experiments in collaboration with PNNL confirm oligomeric species Simulation of Spectrum • Concurrent work by Manners et al. suggests oligomer / polymer distribution is concentration dependent Soluble iridium-catalyzed dehydrogenation products are mixtures of oligomers of varying molecular weights 8 Identifying Soluble Products MeAB Soluble Products Cyclic Products - Acyclic Products - (CH3NH2BH2)(CH3NHBH2)n (CH3NHBH2)n (CH3NH2) Me Me Me Me Me Me Me NH NH H NH BH2 NH B B BH3 H2N NH NH2 H2 y BH2 H B NH Me BH2 2 H2B NH Me n NH BH 2 NH BH2 Linear n x Me Me Macrocycles Cycles with branching Branched Products also Possible Both cyclic and acyclic dehydrogenation products are observed in the MeAB products. 9 Identifying Soluble Products Mixed AB/MeAB Soluble Products Cyclic - Acyclic - (NH2BH2)x(CH3NHBH2)y (NH2BH2)x(CH3NHBH2)y(H)2 Me Me Me H NH2 NH Branched Products NH BH BH2 BH2 NH BH2 y also Possible H2B NH2 H2B NH2 Me Me H2N BH2 H2N BH2 H2N NH NH NH B NH B NH 2 2 H H 2 2 BH2 BH BH2 2 n BH3 Me Me n x Linear Macrocycles Cycles with branching Both cyclic and acyclic dehydrogenation products are observed in the mixed AB/MeAB reactions. Cross-linked products containing both (NH2BH2) and (CH3NHBH2) fragments in a ~1:1 ratio are observed. 10 Extending (POCOP)Ir to the 1st Row [Co] = O O tBu tBu • [Co]H: Reaction with AB afforded t P Co P t Bu Bu minimal dehydrogenation • [Co]?: Reaction with AB led to dehydrogenation of AB (< 1 eq.) and loss of catalyst activity •[Co]N2: Was found to be an active dehydrogenation catalyst for AB. [Co]N2 was present in solution A first row analog of the highly successful following the reaction, along with a (POCOP)Ir catalyst which is active for the dehydrogenation of AB has been identified. solid precipitate (pentamer). Characterization of the active catalyst and collection of rate data is ongoing. 11 Optimization of Cobalt Catalyst •After formation of the active species one equivalent of H2 is generated within 3 min The lifetime of the active catalyst is limited -Evidence of ligand backbone degradation Optimization of cobalt catalyst resulted in dehydrogenation activity approaching the Ir system 12 Design of More Robust Catalysts The tridentate pincer ligand motif has shown good activity for AB dehydrogenation in Ir and Co precatalysts. N N N Co N N N Co Cl R2P PR2 Cl •Carbene based system proved to be •PNP complex exhibits improved an ineffective catalyst stability at 60 oC N P Co P Ph Ph N Cl R P PR Ph Ph 2 Co 2 Cl •A potentially more robust analog of the highly active Si containing •Carbazole based system may catalyst display greater thermal stability Higher temperatures give improved dehydrogenation. This strategy is being pursued with appropriately designed catalysts 13 Dehydrogenation of CBN heterocycles Calculations (U of Alabama) indicate that dehydrogenation of CBN compounds will be endothermic resulting in overall thermodynamics close to thermoneutral. This will allow direct regeneration of the spent material. Compounds received from U of O Compounds anticipated from U of O Reaction Studied: O O [Ir] = tBu tBu t P Ir P t minor product Bu Bu [Ir]H2 is able to dehydrogenate the received material; yields are low. Search for useful catalysts of CBN dehydrogenation is currently underway 14 Future Work • CBN Materials – Collaboration with U of Oregon in synthesis, dehydrogenation and rehydrogenation of CBN materials • Characterization of liquid spent fuels in collaboration with LANL • Development of new transition metal catalysts – Shift metal emphasis • Focus has shifted from Ir based catalysts to Co, Fe – New Ligand Designs • Modify current ligand designs to increase dehydrogenation activity of metal complexes and make complexes more robust at higher temperatures • Investigate ligands capable of participating in ionic dehydrogenation mechanisms 15 Collaborations with Center Partners • PNNL – GPC experiments with soluble MeAB and mixed AB/MeAB dehydrogenation products • University of Oregon – Working closely with Oregon to investigate reactivity of new CBN materials • University of Alabama – Collaborated on obtaining calculations of thermodynamics of CBN target fuels 16 Project Summary • Relevance – BN and CBN compounds have significant potential as hydrogen storage materials which can meet DOE goals • Approach – Develop catalysts for dehydrogenation of BN and CBN systems – Investigate different BN/CBN materials and systems – Optimize systems to meet DOE weight and volume, H2 discharge rate, and system cost targets • Accomplishments – Identified soluble products of mixed MeAB/AB systems – Synthesized direct 1st row metal analog of highly active Ir system – Optimized previously reported highly active Co system – Started active collaboration with U of Oregon towards testing new CBN fuels • Collaboration – Collaborations with groups at PNNL, LANL, University of Alabama, and University of Oregon • Future Work – Develop cheap 1st row metal catalysts with robust ligand backbones – Study dehydrogenation of new CBN materials provided by U of Oregon 17.
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