Off-Set Interactions of Ruthenium-bda Type Catalysts for Promoting Water-Splitting Performance.
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ABSTRACT:
SUBMITTER: Timmer BJJ
PROVIDER: S-EPMC8251529 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The nature of chemical bonds of ruthenium(Ru)-quinine(Q) complexes, mononuclear [Ru(trpy)(3,5-t-Bu(2)Q)(OH(2))](ClO(4))(2) (trpy = 2,2':6',2''-terpyridine, 3,5-di-tert-butyl-1,2-benzoquinone) (1), and binuclear [Ru(2)(btpyan)(3,6-di-Bu(2)Q)(2)(OH(2))](2+) (btpyan = 1,8-bis(2,2':6',2''-terpyrid-4'-yl)anthracene, 3,6-t-Bu(2)Q = 3,6-di-tert-butyl-1,2-benzoquinone) (2), has been investigated by broken-symmetry (BS) hybrid density functional (DFT) methods. BS DFT computations for the Ru complexes have elucidated that the closed-shell structure (2b) Ru(II)-Q complex is less stable than the open-shell structure (2bb) consisting of Ru(III) and semiquinone (SQ) radical fragments. These computations have also elucidated eight different electronic and spin structures of tetraradical intermediates that may be generated in the course of water splitting reaction. The Heisenberg spin Hamiltonian model for these species has been derived to elucidate six different effective exchange interactions (J) for four spin systems. Six J values have been determined using total energies of the eight (or seven) BS solutions for different spin configurations. The natural orbital analyses of these BS DFT solutions have also been performed in order to obtain natural orbitals and their occupation numbers, which are useful for the lucid understanding of the nature of chemical bonds of the Ru complexes. Implications of the computational results are discussed in relation to the proposed reaction mechanisms of water splitting reaction in artificial photosynthesis systems and the similarity between artificial and native water splitting systems.
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Project description:Active phase loss mechanisms from Ru/AC catalysts were studied in continuous supercritical water gasification (SCWG) for the first time by analysing the Ru content in process water with low limit-of-detection time-resolved ICP-MS. Ru loss was investigated alongside the activity of commercial and in-house Ru-based catalysts, showing very low Ru loss rates compared to Ru/metal-oxides (0.2-1.2 vs. 10-24 μg gRu -1 h-1, respectively). Furthermore, AC-supported Ru catalysts showed superior long-term SCWG activity to their oxide-based analogues. The impact on Ru loss of several parameters relevant for catalytic SCWG (temperature, feed concentration or feed rate) was also studied and was shown to have no effect on the Ru concentration in the process water, as it systematically stabilised to 0.01-0.2 μgRu L-1 for Ru/AC. Looking into the type of Ru loss in steady-state operation, time-resolved ICP-MS confirmed a high probability of finding Ru in the ionic form, suggesting that leaching is the main steady-state Ru loss mechanism. In non-steady-state operation, abrupt changes in the pressure and flow rate induced important Ru losses, which were assigned to catalyst fragments. This is directly linked to irreversible mechanical damage to the catalyst. Taking the different observations into consideration, the following Ru loss mechanisms are suggested: 1) constant Ru dissolution (leaching) until solubility equilibrium is reached; 2) minor nanoparticle uncoupling from the support (both at steady state); 3) support disintegration leading to the loss of larger amounts of Ru in the form of catalyst fragments (abrupt feed rate or pressure variations). The very low Ru concentrations detected in process water at steady state (0.01-0.2 μgRu L-1) are close to the thermodynamic equilibrium and indicated that leaching did not contribute to Ru/AC deactivation in SCWG.
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