Highly Efficient Ammonia Borane Hydrolytic Dehydrogenation in Neat Water Using Phase-Labeled CAAC-Ru Catalysts

Abstract

Ammonia borane (AB) has received extensive attention in recent years as an emerging hydrogen storage material due to its high hydrogen density (19.6 wt %), nontoxicity, stability, and water solubility. Although AB itself is stable in water, its catalytic dehydrogenation (2 mol eq) in aqueous media produces borazine whose tandem hydrolytic reaction enables further hydrogen release (1 mol eq). Thus, water serves both as a reaction medium and also a pure hydrogen fuel source (33% of overall released H2). A high capacity and fast homogeneous AB hydrolytic dehydrogenation system is reported using water-soluble CAAC-Ru carbene catalysts (5 and 6). Applying catalyst 6 at 50 ppm (0.015 mM) loading a high TON of 43,600 can be observed; meanwhile, the yield of the released H2 remains high (73%, equal to 2.2 released molH2/molBH3NH3). The evolved hydrogen can achieve 2.9 molH2/molBH3NH3 ([6] = 3.0 mM) and a TON of 86,100 (equal to 1.70 kg H2 (released)/g Ru metal (used)) (10 ppm loading, [6] = 0.003 mM). The energy density of 1.70 kg H2 is equal to that of 6.6 L of gasoline, which is a general consumption for a medium category car/100 km. The reaction yields nonhazardous borates up to 99% yield, which are considered as a recyclable commodity material for hydrogen storage systems. As the metaborate ion (BO2 –)-induced catalyst passivation causing a decrease in accessibility of active sites in heterogeneous catalysis does not occur at homogeneous conditions, the reported high TON values can be achieved within significantly shorter reaction times and lower catalyst concentrations.

High Recyclability Magnetic Iron Oxide‐Supported Ruthenium Nanocatalyst for H2 Release from Ammonia‐Borane Solvolysis

“…The 11 B NMR analysis confirms that full conversion of AB occurred (AB is characterized by a chemical shift in D 2 O of À 23.8 ppm, 1 J BH = 91 Hz, Figure S19), while the concomitant formation of polyborates mixture is identified from broad signals located at 8.3 and 11.9 ppm. [43][44][45] The broadness and shift of the signals slightly differs from the results recently ], [45] and are in better agreement with some equilibrium involving B(OH) 3 /B(OH) 4 À (8.3 ppm), and the triborate B 3 O 3 (OH) 4…”

Metal‐Metal Interactions in Bi‐, Tri‐ and Multinuclear Fe, Ru and Os N‐Heterocyclic Carbene Complexes and their Catalytic Applications

“…Fascinated by their vast catalytic usage in olefin metathesis reactions, ruthenium derivatives have been employed extensively in homogeneous and heterogeneous catalysis, which was also the theme of 2005 Nobel Prize in Chemistry. Especially, homogeneous catalysts based on Ru are becoming gradually popular candidates as they possess high catalytic efficacies and functional group tolerance in several industrially important chemical transformations including C−C coupling, [51] C−H activation, [52] hydrogenation [53] and dehydrogenation [54] reactions. NHC complexes of Ru have been extensively studied as efficient catalytic systems in transfer hydrogenation reactions, [55] and recent developments with these NHC complexes has documented their suitability in biomimetic applications [56] .…”

Intrinsic size‐dependent activity of Pt nanoparticles without masking by heterogeneous oxidation states of Pt for hydrolytic dehydrogenation of NH 3 BH 3

“…8,9 In particular, the hydrolytic dehydrogenation of ammonia borane (AB, NH 3 BH 3 ) has been of interest as an emerging means of hydrogen production due to intrinsic advantages of AB such as stability, nontoxicity, and high hydrogen density and selectivity for practical applications. [10][11][12] In this respect, it has been required to reveal the intrinsic sizedependent activity of catalytic nanoparticles for efficient hydrolytic dehydrogenation of AB, and thus the sizedependent catalytic activity of nanoparticles has been addressed in the nanometric regime and sometimes even in subnanometric one. [13][14][15] Nevertheless, in many cases, the apparent catalytic activity of nanoparticles could be affected not only by the intrinsic particle size effect but also by additional effects such as the nanoparticlesupport interaction and the heterogeneous oxidation states of nanoparticles.…”

“…Catalytic dehydrogenation of liquid‐phase hydrogen storage chemicals is highly promising catalysis for the hydrogen economy 8,9 . In particular, the hydrolytic dehydrogenation of ammonia borane (AB, NH 3 BH 3 ) has been of interest as an emerging means of hydrogen production due to intrinsic advantages of AB such as stability, nontoxicity, and high hydrogen density and selectivity for practical applications 10‐12 . In this respect, it has been required to reveal the intrinsic size‐dependent activity of catalytic nanoparticles for efficient hydrolytic dehydrogenation of AB, and thus the size‐dependent catalytic activity of nanoparticles has been addressed in the nanometric regime and sometimes even in subnanometric one 13‐15 .…”