34
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: not found

      Molecular catalysts for hydrogen production from alcohols

      Read this article at

      ScienceOpenPublisher
      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          The conversion of alcohols to carbonyl compounds and hydrogen: a survey of homogeneous enzymatic and anthropogenic catalytic dehydrogenation reactions.

          Abstract

          An industrially applicable catalytic methodology for dihydrogen formation from a proton source remains at the forefront of all efforts to replace the present fossil fuel economy by a hydrogen economy. This review tries to summarize the achievements which have been made with molecular organometallic complexes as catalysts for the dehydrogenation of alcohols. Biology uses NAD + as a metal-free hydrogen acceptor which converts with the help of enzymes (alcohol dehydrogenase, aldehyde dehydrogenase) alcohols in carbonyl compounds, NADH, and protons. In the regeneration of NADH to NAD +, electrons are stored in electron transfer enzymes (ferredoxines) which are subsequently used to reduce protons to hydrogen with the help of hydrogenases or nitrogenases which ensures a very low overpotential for the reduction. Man-made organometallic complexes are rather primitive with respect to this complex machinery but use some principles from biology as guide lines. Classical complexes like rhodium or ruthenium phosphane complexes achieve at best a few thousands of turn over frequencies (TOFs). Established reactions like oxidative addition of the hydroxyl group of the substrate to the metal centre, β-hydrogen elimination from the α-CH group of the coordinated alcohol, product dissociation, and reductive elimination of hydrogen are involved in the proposed catalytic cycles. Complexes which show metal–ligand cooperativity show a significantly better performance with respect to turn over frequencies (conversion rate = activity) and turn over numbers (number of product molecules per catalyst molecule = efficiency). In these catalytic systems, the alcohol substrate is converted with the help of active centres in the ligand backbone which participate directly and reversibly in the transformation of the substrate. Present results indicate that dehydrogenative coupling reactions of the type, R–CH 2–OH + XH → RCOX + 2H 2, proceed especially well and can be applied to a wide range of substrates including multiple dehydrogenative couplings leading to polyesters or polyamides. In photocatalytic conversions, alcohols can be deoxygenated to hydrocarbons, CO, and H 2 which should be further explored in the future. New developments consist of the construction of organometallic fuel cells (OMFCs) where the anode is composed of molecular catalysts embedded into a conducting support material. Here no free hydrogen is evolved but it is directly converted to electric current and protons according to H 2 → 2H + + 2e. The review focuses on the catalysis with organometallic complexes but lists some selected results obtained with heterogeneous catalytic systems for comparison.

          Related collections

          Most cited references308

          • Record: found
          • Abstract: found
          • Article: not found

          Hydrogen from catalytic reforming of biomass-derived hydrocarbons in liquid water.

          Concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands make hydrogen an attractive alternative energy source. Hydrogen is currently derived from nonrenewable natural gas and petroleum, but could in principle be generated from renewable resources such as biomass or water. However, efficient hydrogen production from water remains difficult and technologies for generating hydrogen from biomass, such as enzymatic decomposition of sugars, steam-reforming of bio-oils and gasification, suffer from low hydrogen production rates and/or complex processing requirements. Here we demonstrate that hydrogen can be produced from sugars and alcohols at temperatures near 500 K in a single-reactor aqueous-phase reforming process using a platinum-based catalyst. We are able to convert glucose -- which makes up the major energy reserves in plants and animals -- to hydrogen and gaseous alkanes, with hydrogen constituting 50% of the products. We find that the selectivity for hydrogen production increases when we use molecules that are more reduced than sugars, with ethylene glycol and methanol being almost completely converted into hydrogen and carbon dioxide. These findings suggest that catalytic aqueous-phase reforming might prove useful for the generation of hydrogen-rich fuel gas from carbohydrates extracted from renewable biomass and biomass waste streams.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            Direct synthesis of amides from alcohols and amines with liberation of H2.

            Given the widespread importance of amides in biochemical and chemical systems, an efficient synthesis that avoids wasteful use of stoichiometric coupling reagents or corrosive acidic and basic media is highly desirable. We report a reaction in which primary amines are directly acylated by equimolar amounts of alcohols to produce amides and molecular hydrogen (the only products) in high yields and high turnover numbers. This reaction is catalyzed by a ruthenium complex based on a dearomatized PNN-type ligand [where PNN is 2-(di-tert-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine], and no base or acid promoters are required. Use of primary diamines in the reaction leads to bis-amides, whereas with a mixed primary-secondary amine substrate, chemoselective acylation of the primary amine group takes place. The proposed mechanism involves dehydrogenation of hemiaminal intermediates formed by the reaction of an aldehyde intermediate with the amine.
              Bookmark
              • Record: found
              • Abstract: not found
              • Article: not found

              A review of anode catalysis in the direct methanol fuel cell

                Bookmark

                Author and article information

                Journal
                EESNBY
                Energy Environ. Sci.
                Energy Environ. Sci.
                Royal Society of Chemistry (RSC)
                1754-5692
                1754-5706
                2014
                2014
                : 7
                : 8
                : 2464-2503
                Affiliations
                [1 ]ETH Zürich
                [2 ]Department of Chemistry and Applied Biosciences
                [3 ]CH-8093 Zürich, Switzerland
                [4 ]Lehn Institute of Functional Materials (LIFM)
                [5 ]Sun Yat-Sen University
                Article
                10.1039/C4EE00389F
                c554850a-b9a6-4c4a-8fdb-3aa910a10d22
                © 2014
                History

                Comments

                Comment on this article