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

• Pd NPs supported ordered mesoporous were synthesized. • Pd NPs were characterized by XPS, XRD, TEM, SEM, FT-IR and NMR spectroscopy. • Catalyst loading, temperature, NaOH and NaBH 4 concentration effects were examined. • Pd NPs catalyze the hydrolytic production of H 2 from NaBH 4 with TOF of 176 mole H2 .mol cat −1 .min −1 . • Pd NPs catalyst retains 71.6% of its initial catalytic activity after five cycles. 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 Na 2 PdCl 4 followed by in situ reduction by NaBH 4 . The obtained supported Pd NPs 2 and 6 were fully characterized by XPS, XRD, TEM, SEM, FT-IR and solid-state 29 Si and 13 C NMR spectroscopy. The effect of several parameters such as catalyst loading, temperature, NaOH and NaBH 4 concentration were examined to obtain the optimum reaction conditions. The supported Pd NPs 2 and 6 catalyze the hydrolytic production of H 2 from NaBH 4 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 mole H2 .mol cat −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 NaBH 4 with apparent E a of 35.0 and 35.7 kJ mol −1 for 2 and 6 , respectively. The efficiency of catalyst 6 for the hydrolysis of NaBH 4 was investigated in H 2 O and D 2 O and indicated that the reaction is considerably faster in H 2 O than in D 2 O with primary KIE k H /k D = 2.36. In addition, the PdNPs based [KIT-6] mesoporous silica 6 retains 71.6% of its initial efficiency after five cycles.