Oleylamine-stabilized ruthenium(0) nanoparticles catalyst in dehydrogenation of dimethylamine-borane

https://doi.org/10.1016/j.ijhydene.2013.05.119Get rights and content

Highlights

  • Hydrogen generation from the dehydrogenation of dimethylamine-borane at 25 °C.

  • OAm-stabilized Ru(0) nanoparticles are highly active and long lived catalyst.

  • Detailed kinetic study of the catalytic dehydrogenation of dimethylamine-borane.

Abstract

Oleylamine-stabilized ruthenium(0) nanoparticles were in situ generated from the reduction of ruthenium(III) chloride by dimethylamine-borane during its dehydrogenation at room temperature. Nearly monodispersed ruthenium(0) nanoparticles of 1.8 ± 0.7 nm size were reproducibly isolated from the reaction solution by filtration and characterized by TEM, XRD, HRTEM, 11B NMR, ATR-IR and UV–visible spectroscopy. Oleylamine-stabilized ruthenium(0) nanoparticles are highly active catalyst in hydrogen generation from dimethylamine-borane providing a release of 1.0 equivalent H2 per mole of dimethylamine-borane and an initial turnover frequency of 137 (mol H2) (mol Ru)−1 (h)−1 at 25.0 ± 0.5 °C. By considering the activity and stability of ruthenium(0) nanoparticles, the optimum ratio of stabilizer to the catalyst was found to be 3.0. Oleylamine-stabilized ruthenium(0) nanoparticles with a stabilizer to ruthenium ratio of 3.0 are stable and reusable catalyst providing 20,660 turnovers in hydrogen generation from dimethylamine-borane at 25.0 ± 0.5 °C. They preserve 75% of their initial catalytic activity even after the fifth run of dehydrogenation of dimethylamine-borane with the complete conversion of Me2NHBH3 to [Me2NBH2]2 plus 1 equivalent of H2 at room temperature. The report also includes the detailed kinetic study of the dehydrogenation of dimethylamine-borane catalyzed by oleylamine-stabilized ruthenium(0) nanoparticles depending on the catalyst concentration, substrate concentration, and temperature as well as the activation parameters of catalytic reaction calculated from the kinetic data. The poisoning experiments showed that the dehydrogenation of dimethylamine-borane catalyzed by ruthenium(0) nanoparticles is heterogeneous catalysis.

Introduction

The safe and efficient storage of hydrogen is the key in the hydrogen based energy policies [1], [2]. There has been rapidly growing interest for the development of hydrogen storage materials with high volumetric and gravimetric capacity [3]. Boron–nitrogen compounds such as NH3BH3 [4], NR3BH3 [5], NH3B3H7 [6], NH4B3H8 [7], N2H4BH3 [8], have been considered as solid hydrogen storage materials as they have high gravimetric hydrogen storage capacity and inclination for bearing protic (N–H) and hydridic (B–H) hydrogen, which can be discharged and recharged in different chemical processes [9].More importantly, recent reports related to the regeneration of dehydrogenation products reveal the importance of the catalytic dehydrogenation of amine-borane adducts [10], [11].Of particular importance, dimethylamine-borane ((CH3)2NHBH3, DMAB) [12],which has been considered as solid hydrogen storage materials [13], [14], can release hydrogen either by hydrolysis in aqueous solution [15], [16] or dehydrogenation in organic medium [17], [18]. Recent studies show that the catalytic dehydrocoupling of dimethylamine-borane potentially releases up to 3.5 wt% H2 (Equation (1)) [19], [20].

A number of catalysts have recently been developed to improve the rate of H2 elimination from dimethylamine-borane: Rhodium colloids or complexes [21], [22], [23], [24], [25], [26], [27], [28], [29], rhodium(0) nanoparticles [18], [30], [31], ruthenium(0) nanoparticles or complexes [32], [33], [34], rhenium complexes [35], nickel complexes [36], [37], titanocene compounds [38], [39], [40], [41], titanium and zirconium sandwich complexes [40], [42], [43], metal carbonyls [44].While the highest catalytic activity has been achieved by using homogeneous [η5-C5H3-1,3-(SiMe3)2Ti]2 catalyst [43] in dehydrogenation of dimethylamine-borane, herein we report a semi heterogeneous ruthenium(0) nanoparticles catalyst with the highest activity and longest life-time in the same reaction at room temperature. Ruthenium(0) nanoparticles were in situ formed from the reduction of ruthenium(III) chloride by dimethylamine borane and stabilized by oleylamine (OAm). This is the first example of using OAm as stabilizer for the ruthenium(0) nanoparticles and employing them as catalysts in the dehydrogenation of dimethylamine-borane. The OAm-stabilized ruthenium(0) nanoparticles show catalytic activity higher than the heterogeneous catalysts reported for the dehydrogenation of dimethylamine-borane [32], [33].They provide an initial turnover frequency of 137 h−1 in generation of 1 equivalent H2 per mole of dimethylamine-borane (Me2NHBH3) which is converted to cyclic aminoborane ([Me2NBH2]2). Our report also includes the results of kinetic study on the hydrogen generation from the dehydrogenation of dimethylamine-borane catalyzed by OAm-stabilized ruthenium(0) nanoparticles depending on the catalyst concentration, substrate concentration, and temperature as well as the activation parameters (Ea, ΔH# and ΔS#) of catalytic dehydrogenation of dimethylamine-borane calculated from the kinetic data. Further experiments performed to determine the catalytic lifetime showed that OAm-stabilized ruthenium(0) nanoparticles provide 20,660 turnovers in hydrogen generation from the dehydrogenation of dimethylamine-borane at room temperature. Moreover, the OAm-stabilized ruthenium(0) nanoparticles exhibit high durability throughout their catalytic use in the dehydrogenation reaction against agglomeration and previously unprecedented reusability in the dehydrogenation of dimethylamine-borane.

Section snippets

General and materials

All commercially obtained chemicals were used as received unless indicated otherwise. Carbon disulfide (CS2), oleylamine (cis-1-amino-9-octadecene, OAm), ruthenium(III) chloride (RuCl3), dimethylamine-borane and toluene were purchased from Sigma–Aldrich®. Toluene was distilled over sodium under nitrogen atmosphere for 12 h. All glassware and Teflon-coated magnetic stir bars were washed with acetone and copiously rinsed with distilled water before drying in an oven at 150 °C.

Equipment

The dehydrogenation

In situ formation of oleylamine-stabilized ruthenium(0) nanoparticles and concomitant catalytic dehydrogenation of dimethylamine-borane

Formation of ruthenium(0) nanoparticles from the reduction of ruthenium(III) chloride by dimethylamine-borane and dehydrogenation of dimethylamine-borane occur concomitantly in the same reactor. In a typical experiment, for example, performed by starting with 2.0 mM ruthenium(III) chloride, 6.0 mM oleylamine and 200 mM dimethylamine-borane in 5.0 mL toluene at room temperature, the color of solution changes from orange to dark brown within less than 15 min, indicating the formation of

Conclusions

In summary, our study on the formation and characterization of OAm-stabilized ruthenium(0) nanoparticles catalyst in the dehydrogenation of dimethylamine-borane led to the following conclusions and insights:

  • 1.

    OAm-stabilized ruthenium(0) nanoparticles were reproducibly formed during the dehydrogenation of dimethylamine-borane starting with a commercially available precursor.

  • 2.

    That an increasing catalytic activity was observed after a certain period of time (induction time) in each case is indicative

Acknowledgments

Partial support by Turkish Academy of Sciences and Bingöl University Scientific Research Projects Unit is gratefully acknowledged.

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