Efficient Hydrogen Evolution from Sodium Borohydride Catalyzed by Palladium Nanoparticles Stabilized by Amine-Decorated Cross-Linked Polymer Immobilized Ionic Liquids

Palladium nanoparticles stabilised by confinement in crosslinked amine-decorated polymer immobilised ionic liquids catalyse the hydrolytic evolution of hydrogen from NaBH₄ under mild conditions. A series of three PIIL supports NH₂-Im_xPIIL (<strong>1a</strong>-<strong>c</strong>, x = 1 (<strong>1a</strong>), x = 2 (<strong>1b</strong>), x = 3 (<strong>1c</strong>), 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 <strong>1a</strong> and <strong>1b</strong> contain one and two imidazolium cations, respectively, while <strong>1c</strong> is a more extensive tris(styryl)-based crosslinker with three imidazolium cations. The composition of the support influences the performance of the PdNPs as catalysts for the hydrolysis of NaBH₄ and a comparison with the corresponding unmodified polymer (PdNP@H-Im₂PIIL) 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 molH₂.molPd^-1.min^-1and 32 molH₂.molPd^-1.min^-1obtained 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 reuses studies showed that PdNP@NH₂-Im₂PIIL recycled with remarkable efficiency as high conversion 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 and supports the beneficial effect of introducing the crosslinking on catalyst longevity.