One-pot synthesis and characterization of colloidally robust rhodium(0) nanoparticles catalyst: Exceptional activity in the dehydrogenation of ammonia borane for chemical hydrogen storage

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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: TUĞÇE AYVALI

Danışman: SAİM ÖZKAR

Özet:

The production of transition metal(0) nanoparticles with controllable size and size distribution are of great importance in catalysis since their catalytic activity decreases as nanoparticles aggregate into clumps and ultimately to the bulk metal. Reducing the particle size of heterogeneous catalyst provides a significant rise in its activity as the fraction of surface atoms increases with decreasing particle size. Therefore, transition metal(0) nanoparticles need to be stabilized to certain extend in their catalytic applications by strong stabilizers. In this regard, tert-butylammonium octanoate [(CH3)3CNH3+][CH3(CH2)6COO-] seems to be an appropriate stabilizer for rhodium(0) nanoparticles since octanoate anion and its associated tert-butylammonium cation can provide a sufficient protection for rhodium(0) nanoparticles against aggregation by the combined electrostatic and steric effects. We report herein the preparation and characterization of rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate and their catalytic use in the dehydrogenation of ammonia borane, H3NBH3, which appears to be the most promising hydrogen storage material due to its high hydrogen content (19.6 wt %). Rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate were reproducibly prepared by the reduction of rhodium(II) octanoate dimer with tert-butylamine borane in toluene at room temperature and characterized by EA, XRD, ICP/OES, TEM, HRTEM, STEM, FTIR, XPS, UV-VIS and NMR spectroscopy. The new rhodium(0) nanoparticles is the first example of well-defined, reproducible, and isolable true heterogeneous catalyst used in the dehydrogenation of ammonia borane. They show record catalytic activity in the dehydrogenation of ammonia borane at room temperature with an apparent initial TOF value of 342 h-1 and TTO value of 1100.