Palladium mesoporous nanoparticles Pd NPs@[KIT-6] and Pd NPs@[KIT-6]-PEG-imid as efficient heterogeneous catalysts for H2 production from NaBH4 hydrolysis

Abstract

The ordered mesoporous silica supported Pd NPs, denoted as Pd NPs@[KIT-6] 2 and Pd NPs@[KIT-6]-PEG-imid 6, were synthesized by a deposition precipitation method using the [KIT-6] 1 or [KIT-6]-PEG-imid 5, respectively, and Na2PdCl4 followed by in situ reduction by NaBH4. The obtained supported Pd NPs 2 and 6 were fully characterized by XPS, XRD, TEM, SEM, FT-IR and solid-state 29Si and 13C NMR spectroscopy. The effect of several parameters such as catalyst loading, temperature, NaOH and NaBH4 concentration were examined to obtain the optimum reaction conditions. The supported Pd NPs 2 and 6 catalyze the hydrolytic production of H2 from NaBH4 with notable efficiencies and the catalyst stabilized by PEG and imidazolium ionic liquid based-[KIT-6] 6 is more active than its [KIT-6] counterpart 2. A TOF of 176 moleH2.molcat−1.min−1 for 6 was achieved when the reaction was performed with a low catalyst loading of 0.1 mol%. Reaction kinetics studies showed that the hydrolysis is first order in catalyst and NaBH4 with apparent Ea of 35.0 and 35.7 kJ mol−1 for 2 and 6, respectively. The efficiency of catalyst 6 for the hydrolysis of NaBH4 was investigated in H2O and D2O and indicated that the reaction is considerably faster in H2O than in D2O with primary KIE kH/kD = 2.36. In addition, the PdNPs based [KIT-6] mesoporous silica 6 retains 71.6% of its initial efficiency after five cycles.