Hydrogen Production by Alkane and Carbinol Dehydrogenation
Hydrogen Production by Alkane and Carbinol Dehydrogenation Catalyzed with Organometallic Complexes
Tech Area / Field
- CHE-SYN/Basic and Synthetic Chemistry/Chemistry
- NNE-FUE/Fuels/Non-Nuclear Energy
3 Approved without Funding
INEOS (Organo-Element Compounds), Russia, Moscow
- The University of Montana, Chemistry Department, USA, MT, Missoula\nIndiana University / Department of Chemistry, USA, IN, Bloomington
Project summaryAt present the main source of energy for humanity is fossil fuel, mainly petroleum and natural gas (methane is main constituent of natural gas). By burning many million tons oil in year, we steadily increase greenhouse gas, CO2, concentration in atmosphere, as well as other pollution of environment. At the same time, the proven reserves of fossil fuel are progressively decreasing. Currently used methods for transformation of hydrocarbons into valuable chemicals, such as olefins and other products and feedstocks for chemical industry are based mainly on the use of heterogeneous catalysts. These processes are conducted under very severe conditions, at high temperatures, and, as a result, with low selectivity (R.B. Bergman, Nature, 2007, 446, 391-393). As a consequence, emissions of pollutions and extra energy consumption occur. The solving of energy problem and rational use of fossil fuel can be, respectively, a search for alternative renovanable sources of energy and the development of highly selective processes of alkane transformation for production of valuable products for chemical industry. Dihydrogen, as the purest fuel, has for a long time attracted attention of scientists (N. Armalori, V. Balzani, Angew. Chem. Int. Ed., 2007, 46, 52-66). Only pure water is formed in fuel cells when dihydrogen is used for energy production. Production of hydrogen by catalytic water splitting could solve for ever the energy problems for humanity. Evidently, this challenge will ultimately be solved sooner or later, very likely by the application of metallocomplex catalysis. At the same time, the advantages of organometallic chemistry and metallocomplex catalysis fot alkane activation are very impressive (A.E. Shilov, G.B. Shul’pin, Chem. Rev., 1997, 97, 2879-2932; J.A. Labinger, J.E. Bercaw, Nature, 2002, 417, 507-514). Particularly, the efficient homogeneous catalysts for alkane activation/functionalization have been created. This gave basis for the development of practically important catalytic systems for production of dihydrogen and olefins by alkane dehydrogenation, and dihydrogen by carbinols dehydrogenation. Dihydrogen obtained in these processes should be high purity and applicable for the use in fuel cells, as well as a chemical reagent. As for selective production of olefins – the main hydrocarbon feedstock for chemical industry, directly from alkanes in one step, it is a global problem of organic chemistry and metallocomplex catalysis.
Research Objectives. The present project is aimed to develop and create a new family of practical catalysts, based on so-called pincer complexes. Pincer complexes of a new generation containing chelated bis(phosphine) ligands with metallocene backbone, were developed by the participants of the project headed by Prof. A.A. Koridze (A.A. Koridze, A.M. Sheloumov, S.A. Kuklin, V.Yu. Lagunova, I.I. Petukhova, P.V. Petrovskii, A.A. Macharashvili, R.V. Chedia, Russ. Chem. Bull, Int. Ed., 2002, 51, 1077-1078). Peculiarity of these complexes, in comparison with the known benzene-based pincer complexes (M.E. van der Boom, D. Milstein, Chem. Rev, 2003, 103, 1759-1792) is the possibility to alter stereochemistry and electron density at the catalytic center within wider limits. It allows us to carry out fine tuning of pincer complexes for practical application in catalytic reactions. It has been shown recently (S.A. Kuklin, A.M. Sheloumov, F.M. Dolgushin, M.G. Ezernitskaya, A.S. Peregudov, P.V. Petrovskii, A.A. Koridze, Organometallics, 2006, 25, 5466-5476) that created in the group of Prof. A.A. Koridze iridium bis(phosphine) pincer complexes with metallocene backbone are the most active among the known homogeneous catalysts for alkane dehydrogenation. It was found by the same group, that the similar iridium complexes can perform dehydrogenation of secondary carbinols under mild conditions without addition of sacrificial acceptor and base to formation dihydrogen and ketones. The project objective is the creation of practical catalysts for dehydrogenation of alkanes and carbinols with formation of dihydrogen and olefins in the first case, and dihydrogen and ketones in the second case. This objective can be pided into sub-objectives as detailed below:
1. The elaboration of bis(phosphine) and bis(N-heterocyclic carbene) pincer complexes based on metallocenes and benzene containing functional groups at aromatic rings for the subsequent immobilization of the corresponding pincer complexes.
2. The elaboration of synthetic methods for the preparation of iridium, rhodium, and ruthenium pincer complexes with above mentioned pincer ligands. The effects of steric and electronic properties of the pincer ligands and the nature of the chelated metal atom on the inpidual steps of the catalytic cycle of alkanes and carbinols dehydrogenation will be studied.
3. The elaboration of methods for immobilization of pincer complexes, aimed to create the practical catalysts. Two approaches will be used for immobilization of the most promising catalysts for alkanes and carbinols dehydrogenation: the classical, based on immobilization on polymers, and novel based on the application of nano-structured metallic supports.
4. Testing of immobilized complexes as catalysts for dehydrogenation of alkanes and carbinols. Optimization of conditions for selective dehydrogenation as a continuous reactions of alkane dehydrogenation with formation of dihydrogen and olefins and dehydrogenation of secondary carbinols with formation of dihydrogen and ketones.
As a result of the endeavor, novel approaches to the design and synthesis of efficient and selective catalysts for dehydrogenation of alkanes and carbinols will be elaborated.
Participants of the Project. The participants of the project have disclosed a new generation of the pincer complexes – binuclear pincer complexes based on metallocenes (A.A. Koridze, A.M. Sheloumov, S.A. Kuklin, V.Yu. Lagunova, I.I. Petukhova, P.V. Petrovskii, A.A. Macharashvili, R.V. Chedia, Russ. Chem. Bull, Int. Ed., 2002, 51, 1077-1078). At present they occupy leading position in the field of pincer complexes of platinum group metals with metallocene backbone –complexes of rhodium, iridium, palladium, ruthenium, and osmium have been synthesized, and these results are published in the leading Russian, European and USA journals (see, for example, A.A. Koridze, S.A. Kuklin, A.M. Sheloumov, V.Yu. Lagunova, I.I. Petukhova, A.S. Peregudov, E.V. Vorontsov, M. Baya, R. Poli, Ferrocene-based pincer complexes of palladium: synthesis, structures, and spectroscopic and electrochemical properties, Organometallic, 2004, 23, 4585-4593; A.M. Sheloumov, F.M. Dolgushin, M.V. Kondrashov, P.V. Petrovskii, Kh.A. Barbakadze, O.I. Lakashvili., A.A. Koridze, Ruthenium complexes with ferrocene-based P,C,P pincer ligand, Russ. Chem. Bull, Int. Ed., 2007, 56, 1757-1764). It was recently demonstrated (S.A. Kuklin, A.M. Sheloumov, F.M. Dolgushin, M.G. Ezernitskaya, A.S. Peregudov, P.V. Petrovskii, A.A. Koridze, Highly active iridium catalysts for alkane dehydrogenation. Synthesis and properties of iridium bis(phosphine) pincer complexes based on ferrocene and ruthenocene, Organometallics, 2006, 25, 5466-5476) that iridium bis(phosphine) pincer complexes based on ferrocene and ruthenocene are the most active among all known homogeneous catalysts for alkane dehydrogenation. Participants of the project have recently successively accomplished the work on the ISTC project # 3082; particularly all objectives, claimed in this project, have been realized. The present project is the logical continuation of the work, carried out according to the project # 3082.
Expected Results and Their Application. The methods for the synthesis of metallocene-based bis(phosphine) and bis(N-heterocyclic carbene) pincer complexes of platinum metals will be elaborated. We plan to establish the structure/reactivity relationships in the activation of C-H bonds of alkanes and carbinols with the above mentioned complexes, to study the role of steric and electronic factors and the nature of the platinum metal in the processes of dehydrogenation of alkanes and carbinols. The study of inpidual steps of the reactions by experimental and theoretical methods will allow us to shed light on the mechanisms of the inpidual steps of the catalytic cycle. The most promising complexes will be used as basic units for immobilization on polymeric and nanostructured metal supports in order to create practical catalysts. The creation of efficient catalysts for dehydrogenation of alkanes and carbinols with formation of pure hydrogen and olefins in the first case, and hydrogen and ketones in the second case, can exert the huge influence on the efficiency of petrochemical procecces of alkane transformations; the availability of hydrogen as ecologically irreproachable fuel could have tremendous environmental and economic impact.
Meeting ISTC Goals and Objectives. The project will fulfill the objectives of ISTC in the following way: providing weapons scientists and engineers opportunities to redirect their talents to peaceful activities; promoting integration of scientists into the international scientific community; supporting basic and applied research and technology development for peaceful purposes; reinforcing the transition to market-based economics responsive to civil needs.
Role of Foreign Collaborators
Information exchange during the execution of the Project; carring out joint experiments and investigation of complexes synthesized; discussions of obtained experimental results; joint publications; offering of conclusions on Technical Reports (quarterly, annual, and final) submitted to ISTC by Project executors; conducting some experiments at the laboratories of Western collaborators.
Technical Approach and Methodology. Applying group discovered a new generation bis(phosphine) pincer complexes based on metallocenes. They have also demonstrated that iridium pincer complexes of a new generation are active catalysts for alkane dehydrogenation. The approach to the creation of catalysts based on pincer complexes with metallocene backbone as advantageous, since it allows alternation of the steric environment and electronic properties at the chelated metal atom within wider range, than it is possible for the common pincer complexes. Another peculiarity of the ferrocene-based systems includes the ability of the iron atom to be oxidized reversibly, which can turn out a useful property for some catalytic processes. And finally, we plan to use in this project the original approach for immobilization of homogeneous dehydrogenation catalysts. It consists in anchoring of pincer complexes into the porous nanostructured metal particles. This method will allow us to conduct dehydrogenation process in continuous regime, and at the same time to increase working time of catalysts.
All experiment will be accompanied by X-ray diffraction studies of the complexes generated. Multinuclear NMR, IR, and electrochemical studies will be performed to give better understanding of electronic structure of compounds of interest. The isotopic H/D effects will be used for elucidation of the reaction mechanisms.
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