Back-clocking of Fe2+/Fe1+spin states in a H2-producing catalyst by advanced EPR

Stathi, Panagiota; Mitrikas, George; Sanakis, Yiannis; Louloudi, Maria; Deligiannakis, Yiannis

doi:10.1080/00268976.2013.798045

Cited by 8 publications

(3 citation statements)

References 21 publications

(52 reference statements)

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“…This has been confirmed by our recent studies using advanced Pulsed-EPR spectroscopy [7]. Taking into account the key importance of FA deprotonation for efficient H 2 production, here we evaluated the co-catalytic activity of SiO 2 and surface-modified L@SiO 2 particles on the catalytic performance of the reference Fe II /P(CH 2 CH 2 PPh 2 ) 3 homogeneous system.…”

Section: Introductionsupporting

confidence: 72%

Co-catalytic Effect of Functionalized SiO₂ Materials on H₂ Production from Formic Acid by an Iron Catalyst

2014

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Surface modified L@SiO 2 particles bearing covalently attached functional groups (L) have been tested as co-catalysts for H 2 production from Formic Acid (FA) by the homogenous Fe II /P(CH 2 CH 2 PPh 2 ) 3 catalyst. The L@SiO 2 particles induce remarkable increase of catalytic H 2 production i.e. by 710 %, when L=a basic functionality such as Imidazoles, or NH 2 -groups. This effect is attributed to a thermodynamic promotion of FA deprotonation facilitating coordination of HCOOanion on the Fe II atom of active catalyst during catalysis. INTRODUCTIONH 2 production is of critical importance for chemical industry and the environment. Last decade's research focused two main issues: [i] developing efficient, low-cost catalysts via environmentally sustainable technologies using earth abundant row materials, low-energy consumption, environmental friendly management after end-of-life; [ii] Utilizing alternative feedstocks to generate hydrogen e.g. from byproducts of other mature technologies such as biomass processing. Thus, formic acid (FA), a major byproduct of biomass processing, formally an adduct of H 2 and CO 2 , has attracted considerable attention as a suitable liquid source for H 2 .In this context, in 2010, a breakthrough was achieved by Beller et al [1,2], showing that low-cost Fe-phosphine complexes can successfully catalyze H 2 production from FA at near-ambient temperatures, with zero CO generation. Among them, the most efficient/simple and low-cost system includes Fe II and tris[(2-diphenylphosphino)ethyl] phosphine, P(CH 2 CH 2 PPh 2 ) 3 , to a solution of propylene carbonate with no further additives [2].It has been proposed that a key catalytic step for H 2 production by FA is the coordination of one deprotonated HCOO -molecule on the metal centre [3][4][5][6]. This has been confirmed by our recent studies using advanced Pulsed-EPR spectroscopy [7]. Taking into account the key importance of FA deprotonation for efficient H 2 production, here we evaluated the co-catalytic activity of SiO 2 and surface-modified L@SiO 2 particles on the catalytic performance of the reference Fe II /P(CH 2 CH 2 PPh 2 ) 3 homogeneous system. Herein we have synthesized L@SiO 2 particles bearing covalently attached functional groups: imidazole, -Cl, -COOH, or -NH 2 . Our results reveal significant increase of catalytic H 2 production in the presence of materials which bear basic L functionalities of SiO 2 surface.

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Section: Introductionsupporting

confidence: 72%

Co-catalytic Effect of Functionalized SiO₂ Materials on H₂ Production from Formic Acid by an Iron Catalyst

2014

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“…All existing literature data show that the molecular mechanism of FA dehydrogenation does not involve metal redox reactions (the metal oxidation state stays stable during the catalytic cycle) [16,43,47,49] This is corroborated by spectroscopic studies i.e., EPR [50], NMR, and Uv-Vis [51] data, as well as by theoretical quantum chemical modelling studied.…”

Section: Outline Of the Catalytic Mechanismssupporting

confidence: 62%

From Homogeneous to Heterogenized Molecular Catalysts for H2 Production by Formic Acid Dehydrogenation: Mechanistic Aspects, Role of Additives, and Co-Catalysts

et al. 2020

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H2 production via dehydrogenation of formic acid (HCOOH, FA), sodium formate (HCOONa, SF), or their mixtures, at near-ambient conditions, T < 100 °C, P = 1 bar, is intensively pursued, in the context of the most economically and environmentally eligible technologies. Herein we discuss molecular catalysts (ML), consisting of a metal center (M, e.g., Ru, Ir, Fe, Co) and an appropriate ligand (L), which exemplify highly efficient Turnover Numbers (TONs) and Turnover Frequencies (TOFs) in H2 production from FA/SF. Typically, many of these ML catalysts require the presence of a cofactor that promotes their optimal cycling. Thus, we distinguish the concept of such cofactors in additives vs. co-catalysts: When used at high concentrations, that is stoichiometric amounts vs. the substrate (HCOONa, SF), the cofactors are sacrificial additives. In contrast, co-catalysts are used at much lower concentrations, that is at stoichiometric amount vs. the catalyst. The first part of the present review article discusses the mechanistic key steps and key controversies in the literature, taking into account theoretical modeling data. Then, in the second part, the role of additives and co-catalysts as well as the role of the solvent and the eventual inhibitory role of H2O are discussed in connection to the main mechanistic steps. For completeness, photons used as activators of ML catalysts are also discussed in the context of co-catalysts. In the third part, we discuss examples of promising hybrid nanocatalysts, consisting of a molecular catalyst ML attached on the surface of a nanoparticle. In the same context, we discuss nanoparticulate co-catalysts and hybrid co-catalysts, consisting of catalyst attached on the surface of a nanoparticle, and their role in the performance of molecular catalysts ML.

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“…A typical broad integer-spin signal was observed in conventional (perpendicular) detection-mode, whereas with parallel-mode polarization additional sharp features have been resolved . By means of EPR spectroscopy, high-spin iron species were identified previously in synthetic transition metal complexes and biological systems at X-band frequencies ( h ν ≈ 0.3 cm –1 ) under the condition that the axial ZFS parameter is small enough to allow for non-Kramers transitions in the spin manifold. − Because of the intermolecular coupling of compound 1 , we suggest that the EPR signals in our case arise from spin-coupled magnetic states, which partially can have very small contributions from single-ion ZFS due to vanishing spin-projection factors . Unfortunately the spectra can therefore not provide D and E / D for the individual Fe(II) sites.…”

Section: Resultsmentioning

confidence: 68%

Modeling the Active Site of [NiFe] Hydrogenases and the [NiFe_u] Subsite of the C-Cluster of Carbon Monoxide Dehydrogenases: Low-Spin Iron(II) Versus High-Spin Iron(II)

et al. 2014

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A series of four [S2Ni(μ-S)2FeCp*Cl] compounds with different tetradentate thiolate/thioether ligands bound to the Ni(II) ion is reported (Cp* = C5Me5). The {S2Ni(μ-S)2Fe} core of these compounds resembles structural features of the active site of [NiFe] hydrogenases. Detailed analyses of the electronic structures of these compounds by Mössbauer and electron paramagnetic resonance spectroscopy, magnetic measurements, and density functional theory calculations reveal the oxidation states Ni(II) low spin and Fe(II) high spin for the metal ions. The same electronic configurations have been suggested for the Cred1 state of the C-cluster [NiFeu] subsite in carbon monoxide dehydrogenases (CODH). The Ni-Fe distance of ∼3 Å excludes a metal-metal bond between nickel and iron, which is in agreement with the computational results. Electrochemical experiments show that iron is the redox active site in these complexes, performing a reversible one-electron oxidation. The four complexes are discussed with regard to their similarities and differences both to the [NiFe] hydrogenases and the C-cluster of Ni-containing CODH.

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Back-clocking of Fe²⁺/Fe¹⁺spin states in a H₂-producing catalyst by advanced EPR

Cited by 8 publications

References 21 publications

Co-catalytic Effect of Functionalized SiO₂ Materials on H₂ Production from Formic Acid by an Iron Catalyst

Co-catalytic Effect of Functionalized SiO₂ Materials on H₂ Production from Formic Acid by an Iron Catalyst

From Homogeneous to Heterogenized Molecular Catalysts for H2 Production by Formic Acid Dehydrogenation: Mechanistic Aspects, Role of Additives, and Co-Catalysts

Modeling the Active Site of [NiFe] Hydrogenases and the [NiFe_u] Subsite of the C-Cluster of Carbon Monoxide Dehydrogenases: Low-Spin Iron(II) Versus High-Spin Iron(II)

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Back-clocking of Fe2+/Fe1+spin states in a H2-producing catalyst by advanced EPR

Cited by 8 publications

References 21 publications

Co-catalytic Effect of Functionalized SiO2 Materials on H2 Production from Formic Acid by an Iron Catalyst

Co-catalytic Effect of Functionalized SiO2 Materials on H2 Production from Formic Acid by an Iron Catalyst

From Homogeneous to Heterogenized Molecular Catalysts for H2 Production by Formic Acid Dehydrogenation: Mechanistic Aspects, Role of Additives, and Co-Catalysts

Modeling the Active Site of [NiFe] Hydrogenases and the [NiFeu] Subsite of the C-Cluster of Carbon Monoxide Dehydrogenases: Low-Spin Iron(II) Versus High-Spin Iron(II)

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Back-clocking of Fe²⁺/Fe¹⁺spin states in a H₂-producing catalyst by advanced EPR

Co-catalytic Effect of Functionalized SiO₂ Materials on H₂ Production from Formic Acid by an Iron Catalyst

Co-catalytic Effect of Functionalized SiO₂ Materials on H₂ Production from Formic Acid by an Iron Catalyst

Modeling the Active Site of [NiFe] Hydrogenases and the [NiFe_u] Subsite of the C-Cluster of Carbon Monoxide Dehydrogenases: Low-Spin Iron(II) Versus High-Spin Iron(II)