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Lookup NU author(s): Reece Paterson, Adhwa Alharbi, Dr Corinne Wills, Dr Casey Dixon, Professor Lidija Siller, Dr Julian Knight, Dr Simon DohertyORCiD
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).
Ruthenium nanoparticles stabilised by polymer immobilized ionic liquids catalyse the hydrolytic release of hydrogen from sodium borohydride. The composition of the polymer influences performance and ruthenium nanoparticles stabilised by an amine-decorated imidazolium-based polymer immobilised ionic liquid (RuNP@NH2-PIILS) was the most efficient with a maximum TOF of 177 moleH2.molRu-1.min-1, obtained at 30 °C with a catalyst loading of 0.08 mol%; markedly higher than that of 69 molH2.molRu-1.min-1 obtained with 5 wt% Ru/C and one of the highest to be reported for a RuNP catalyst. The apparent activation energy (Ea) of 38.9 kJ mol-1 for the hydrolysis of NaBH4 catalysed by RuNP@NH2-PIILS is lower than that for the other polymer immobilized ionic liquid stabilised RuNPs, which is consistent with its efficacy. Comparison of the initial rates of hydrolysis in H2O and D2O catalysed by RuNP@NH2-PIILS gave a primary kinetic isotope effect (kH/kD) of 2.3 which supports a mechanism involving rate limiting oxidative addition of one of the O-H bonds in a strongly hydrogen-bonded surface-coordinated [BH3H-]----H2O ensemble. The involvement of a surface-coordinated borohydride is further supported by an inverse kinetic isotope effect of 0.65 obtained from a comparison of the initial rates for the hydrolysis of NaBH4 and NaBD4 under the conditions of catalysis i.e., at a high hydride/catalyst mole ratio. Interestingly though, when the comparison of the initial rates of hydrolysis of NaBH4 and NaBD4 was conducted in dilute solution with a hydride/catalyst mole ratio of 1 a kinetic isotope effect (kH/kD) of 2.72 was obtained; this would be more consistent with concerted activation of both an O-H and B-H bond in the rate limiting step, possibly via a concerted oxidative addition-hydride transfer in the surface-coordinated hydrogen-bonded ensemble. Catalyst stability and reuse studies showed that RuNP@NH2-PIILS retained 79% of its activity over five runs; the gradual drop in the initial TOF with run number appears to be due to passivation of the catalyst by the sodium borate by-product as well as an increase in viscosity of the reaction mixture rather than leaching of the catalyst.
Author(s): Paterson R, Alharbi AA, Wills C, Dixon C, Siller L, Chamberlain TW, Griffiths A, Collins SM, Wu KJ, Simmons MD, Bourne RA, Lovelock KRJ, Seymour J, Knight JG, Doherty S
Publication type: Article
Publication status: Published
Journal: Molecular Catalysis
Year: 2022
Volume: 528
Print publication date: 01/08/2022
Online publication date: 01/07/2022
Acceptance date: 24/06/2022
Date deposited: 06/07/2022
ISSN (print): 2468-8274
ISSN (electronic): 2468-8231
Publisher: Elsevier
URL: https://doi.org/10.1016/j.mcat.2022.112476
DOI: 10.1016/j.mcat.2022.112476
ePrints DOI: 10.57711/v6kv-dh64
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