Palladium nanoparticles (PdNP) stabilised by confinement in crosslinked amine-decorated, polymer-immobilised ionic liquids (PIILs) catalyse the hydrolytic evolution of hydrogen from NaBH4 under mild conditions. A series of three PIIL supports NH2-ImxPIIL (x = 1, (2a); x = 2, (2b); x = 3, (2c), where x corresponds to the number of imidazolium cations in the repeat unit) were prepared with an increasing number of imidazolium cations such that bis(styryl)-based crosslinkers 1a and 1b contain one and two imidazolium cations, respectively, while 1c is a more extensive tris(styryl)-based crosslinker with three imidazolium cations. The composition of the support influences the performance of the corresponding polymer immobilised ionic liquid stabilised (PIILS) palladium nanoparticles, PdNP@NH2-ImxPIILS (x = 1, (4a); x = 2, (4b); x = 3, (4c)) as catalysts for the hydrolysis of NaBH4 and a comparison of the most efficient system against its unmodified counterpart (i.e., PdNP@H-Im2PIILS) confirmed that incorporation of the surface coordinated amine improved catalyst performance. Palladium nanoparticles stabilised by NH2-Im2PIIL was the most efficient catalyst and the maximum initial turnover frequency of 81 molH2 molPd−1 min−1 is higher than the 59 and 32 molH2 molPd−1 min−1 obtained with PdNPs supported by NH2-Im1PIIL and NH2-Im3PIIL, respectively, as well as the 19 molH2 molPd−1 min−1 obtained with commercial 10 wt.% Pd/C. The results of kinetic studies, apparent activation energies, and deuterium isotope effects have been compared with those in the literature and support a mechanism involving rate-limiting activation of an O–H bond in water. Catalyst reuse studies showed that PdNP@NH2-Im2PIILS recycled with remarkable efficiency as high conversions were maintained across five runs with the catalyst retaining over 92% of its initial activity, an improvement on the 70% retention of activity with palladium nanoparticles supported by linear amine-modified imidazolium-based polymer, which demonstrates the beneficial effect of introducing crosslinking.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)