научная статья по теме UNEXPECTEDLY HIGH CATALYTIC ACTIVITY OF RUTHENIUM CATALYSTS IN THE HYDROGENATION OF NITROBENZENE Комплексное изучение отдельных стран и регионов

Текст научной статьи на тему «UNEXPECTEDLY HIGH CATALYTIC ACTIVITY OF RUTHENIUM CATALYSTS IN THE HYDROGENATION OF NITROBENZENE»

The article has entered in publishing office 13.01.10. Ed. reg. No. 698

Статья поступила в редакцию 13.01.10. Ред. рег. № 698

UNEXPECTEDLY HIGH CATALYTIC ACTIVITY OF RUTHENIUM CATALYSTS IN THE HYDROGENATION OF NITROBENZENE

A. Kraynov12, E. Gebauer-Henke1, W. Leitner1,23'*, T.E. Müller1'*

1CAT Catalytic Center, ITMC, RWTH Aachen University, Worringerweg 1, D-52074 Aachen, Germany.

* E-mail: thomas.mueller@catalyticcenter.rwth-aachen.de 2Institut für Technische und Makromolekulare Chemie, RWTH Aachen University, Worringerweg 1, 52074 Aachen, Germany 3Max Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany

Referred: 26.01.10 Expertise: 31.01.10 Accepted: 06.02.10

The performance of ruthenium nanoparticles as quasi-homogeneous catalyst for the concurrent hydrogenation of the nitro group and the aromatic ring in nitrobenzene was compared to a classic carbon supported Ru/C catalyst. When the tartaric acid and glycine based ionic liquids [TA2-][N^8888]2 and [Gly-][N+8888], respectively, were used for stabilizing the ruthenium nanoparticles, catalytic activity and selectivity to cyclohexylamine were similar to the Ru/C catalyst. In contrast, Ru nanoparticles stabilised with the dimethylglycine based ionic liquid [Me2Gly-][N+8888] provided high selectivity to aniline. With Ru/C, the hydrogenation of nitrobenzene was faster than of aniline. These observations were rationalised in terms of binding strength of the stabiliser and intermediates to the ruthenium surface and consequent changes in the elementary steps.

Keywords: ruthenium, nanoparticles, heterogeneous catalysis, hydrogenation, nitrobenzene, aniline, cyclohexylamine, ionic liquid, stabilization, surface modification.

ПРОЯВЛЕНИЕ НЕОБЫЧНО ВЫСОКОЙ АКТИВНОСТИ РУТЕНИЕВЫХ КАТАЛИЗАТОРОВ ПРИ ГИДРИРОВАНИИ НИТРОБЕНЗОЛА

А. Крайнов, Е. Гебауэр-Хенке, В. Ляйтнер, Т.Э. Мюллер

Заключение совета рецензентов: 26.01.10 Заключение совета экспертов: 31.01.10 Принято к публикации: 06.02.10

Было произведено сравнение поведения классического нанесенного на углерод рутениевого катализатора и наночас-тиц рутения, используемых как квазигомогенный катализатор в совместном гидрировании нитрогруппы и ароматического кольца нитробензола. Когда ионные жидкости [TA2-][N+8888]2 и [Gly-][N+8888], основанные на винной кислоте и глицине, соответственно, были использованы для стабилизации наночастиц рутения, каталитическая активность и селективность по отношению к циклогексиламину были близки данным, полученным для Ru/C. В противоположность этому наночасти-цы рутения, стабилизированные ионной жидкостью [Me2Gly-][N+8888], основанной на диметилглицине, демонстрируют высокую селективность по отношению к анилину. Эти наблюдения были объяснены в терминах силы адсорбционного взаимодействия стабилизатора и промежуточных продуктов с поверхностью рутения и последовательных изменений в этапах реакции.

Ключевые слова: рутений, наночастицы, гетерогенный катализ, гидрогенизация, анилин, циклогексиламин, ионная жидкость, стабилизация, модификация поверхности.

Alexander Kraynov was born in 1980 in Orenburg, Russia. He studied physics at Novosibirsk State University and received his bachelor and master degree working at Boreskov Institute of Catalysis. In 2003, he started his Ph.D. in chemistry at Jacobs University Bremen and in 2006 joined the group of Prof. Leitner at RWTH Aachen University. Since 2007, he works at CAT Catalytic Center as a postdoctoral researcher. His current research interest lies in the field of ionic liquids, nanosized materials and catalysis.

Ewa Gebauer-Henke was born in Lodz, Poland in 1978. She received her Diploma at the Technical University of Lodz in 2002 for studies on the selective reduction of a,P-unsaturated aldehydes. She joined the research group of Prof. Rynkowski and received her Ph.D. degree in 2008 for her work on supported catalysts in the selective hydrogenation of crotonaldehyde in gas and liquid phase. In 2008, she moved to RWTH Aachen University for postdoctoral research on amine synthesis and selective hydrogenation over heterogeneous catalysts. She has co-authored 15 publications. Her current research interest is focused on heterogeneous catalysis, synthesis and characterization of catalysts, multiphase reactions, and selective hydrogenation reactions in gas and liquid phase.

Ewa Gebauer-Henke

Walter Leitner

Professor Walter Leitner was born in 1963. He studied chemistry before completing his doctorate at the University of Regensburg, to which he returned after a one-year postdoctoral stay at the University of Oxford as a Liebig-Fellow. In 1991, he joined the newly formed Working Group "CO2 chemistry" of the Max Planck Society at the University of Jena, where he obtained his "Habilitation" in 1995. After nearly seven years in senior positions at the Max Planck Institute for Coal Research in Mülheim an der Ruhr, he accepted an appointment to the Chair of Technical Chemistry and Petrochemistry of the RWTH Aachen University in 2002. In addition to activities on the board of CAT Catalytic Center as scientific director, the German Society for Catalysis (GeCATS) and the Sustainable Chemistry Section of the German Chemical Society (GDCh), he is also the scientific editor of Green Chemistry. His scientific interests are centred on homogeneous catalysis with transition metal complexes and the use of supercritical carbon dioxide for environmentally benign chemical processes. He has been awarded the Wöhler Prize by the German Chemical Society for his innovative contribution to the development of sustainable chemical processes.

Thomas E. Müller

Thomas E. Müller was born in Landshut, Germany in 1967. He received his undergraduate education at LMU München and ETH Zürich. For his Diploma project, he worked with D. M. L. Goodgame, IC London, on coordination polymers. After returning to Switzerland, he received his Diploma in 1991. He joined the research group of D. M. P. Mingos at IC London and received his Ph.D. degree in 1995 for studies on polyaromatic phosphines and their coordination to noble metals. In 1995, he moved to the University of Sussex to pursue postdoctoral research on fullerenes and nanotubes. For his habilitation, he joined the group of J. A. Lercher at TU München in 1998. In 2003, he continued at TU München as Privatdozent. After visiting professor positions at NUS Singapore (2005) and the University of Tokyo (2005), he accepted the position as head of CAT Catalytic Center, RWTH Aachen University, in 2007. He has published more than 50 papers, mainly in the field of catalyst immobilization, amine synthesis, and mechanistic studies on hydroamination, reductive amination, and hydrogenation of nitriles. His current research interest is focused on homogeneous catalysis with transition metal complexes, immobilization of homogeneous catalysts, supported ionic liquids and metal nanoparticles, multiphase reactions, and building block systems for heterogeneous catalysis.

Introduction

Alicyclic amines are important intermediates in the chemical and pharmaceutical industry [1]. They are obtained readily by hydrogenation of the aromatic ring in substituted anilines [2-9]. Frequently, the anilines are obtained by reduction of the corresponding nitro aromatics (Scheme 1) [10-12].

1 3H2, -2H2O

jy Catalyst

no2

3H,

Catalyst

Scheme 1. Synthesis of alicyclic methylcyclohexylamine by reduction of nitrotoluenes

We, thus, became interested in heterogeneous-catalytic protocols allowing the simultaneous reduction of the nitro group and aromatic ring in nitrotoluidines. Controlling the chemoselectivity with respect to formation of primary and secondary amines and alcohols, the cis/trans stereochemistry in the primary amines, and the enantioselectivity in this reaction is of particular interest in the production of pharmaceuticals [13].

To our knowledge, the open literature provides no examples of the direct transformation of nitrotoluenes to

alicyclic amines using heterogeneous catalysts. Also for the hydrogenation of nitrobenzene to cyclohexylamine, only few reports have been published [14, 15]. We report herein on a comparison of the performance of ionic liquid stabilised ruthenium nanoparticles as quasi-homogeneous catalyst and a conventional supported Ru/C nanocomposite catalyst in the hydrogenation of nitrobenzene to cyclohexylamine evaluating the impact of the dimensional factor and of additives on catalytic activity and selectivity.

Experimental

Materials and instrumentation

The chemicals 6/'s-(2-methylallyl)(1,5-cyclo-octadiene)ruthenium(II), ruthenium on activated charcoal (5 wt%), (R^)-tartaric acid, glycine, dimethylglycine, Ambersep 900 OH anion exchange resin, tetraoctylammonium bromide, acetophenone were obtained from Aldrich and used as received. Silica gel 60 (0.04-0.063 mm) was obtained from Merck. Solvents were reagent grade, dried and distilled before use following standard procedures.

For gas chromatographic analyses, a TRACE GC ULTRA from Thermo Scientific instrument equipped with a 50 m CP-Sil-PONA-CB capillary column and FID detector was used.

International Scientific Journal for Alternative Energy and Ecology № 4 (84) 2010

© Scientific Technical Centre «TATA», 2010

Preparation of ionic liquids For the preparation of a methanolic solution of tetraoctylammonium hydroxide, a chromatographic column (100 ml volume) was filled half with the hydroxide loaded anion exchange resin Ambersep 900 OH. The resin was washed slowly with distilled water (300 ml) and subsequently with aqueous methanol (100 ml, 60%). Tetraoctylammonium bromide (4.035 g, 7.38 mmol) dissolved in aqueous methanol (170 ml, 60%) was passed over the column during 1 hour. The resin was washed with aqueous methanol (ca. 100 ml, 60%) until no more hydroxide was determined in the eluent by analysis with a solution of AgNO3 in HNO3. Similarly, the absence of bromide ions in the combined fractions was confirmed by analysing a samp

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