Ruthenium(III) acetylacetonate as catalyst precursor in the dehydrogenation of dimethylamine-borane

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Kimya Bölümü, Türkiye

Tezin Onay Tarihi: 2011

Öğrenci: EBRU ÜNEL

Danışman: SAİM ÖZKAR

Özet:

Amine boranes have recently been considered as solid hydrogen storage materials with high capability of hydrogen storage. Dimethylamine borane is one of the promising amine boranes with high theoretical gravimetric capacity of 16.9 wt%. Dimethylamine borane can undergo dehydrogenation only in the presence of a suitable catalyst at moderate temperature. In this project, throughout the dehydrogenation of dimethylamine borane (DMAB), the catalytic activity of ruthenium(III) acetylacetonate was examined for the first time. During the catalytic reaction, formation of a new in-situ ruthenium(II) species, [Ru{N2Me4}3(acac)H], is observed. Mercury poisoning experiment indicates that the in-situ ruthenium(II) species is a homogeneous catalyst in the dehydrogenation of dimethylamine borane. Kinetics of catalytic dehydrogenation of dimethylamine borane starting with ruthenium(III) acetylacetonate was investigated depending on catalyst concentration, substrate concentration and temperature. As a result, the hydrogen generation rate was found to be first-order with respect to catalyst concentration and zero-order regarding the substrate concentration. Besides, evaluation of the kinetic data yielded that the activation parameters for dehydrogenation reaction: the activation energy, Ea = 85 ± 2 kJ•mol-1; the enthalpy of activation, DH# = 82 ± 2 kJ•mol-1 and the entropy of activation; DS# = -85 ± 5 J•mol-1•K-1. Additionally, before deactivation, [Ru{N2Me4}3(acac)H] provides 1700 turnovers over 100 hours in hydrogen evolution from the dehydrogenation of dimethlyamine borane. [Ru{N2Me4}3(acac)H] complex formed during the dehydrogenation of dimethylamine borane was isolated and characterized by UV-Visible, FTIR, 1H NMR, and Mass Spectroscopy. The isolated ruthenium(II) species was also tested as homogeneous catalyst in the dehydrogenation of dimethylamine borane.