Intrinsic size-dependent activity of Pt nanoparticles without masking by heterogeneous oxidation states of Pt for hydrolytic dehydrogenation of NH₃BH₃

We report size-dependent activity of Pt nanoparticles for hydrolytic dehydrogenation of ammonia borane (AB, NH₃BH₃) in the size range of 1 to 4 nm without masking by heterogeneous oxidation states of Pt. Specifically, we synthesized five differently sized Pt nanoparticles encapsulated inside generation 6 poly(amidoamine) dendrimers with a uniform oxidation state of Pt in an effort to study the intrinsic size effect of Pt nanoparticles on their catalysis. The five differently sized Pt nanoparticles exhibited significant catalytic activity for hydrolytic dehydrogenation of AB under mild conditions. Interestingly, we found that the catalytic activity of the Pt nanoparticles encapsulated inside dendrimers was tunable even with the subnanometer changes in the sizes of Pt nanoparticles in the range of small sizes less than 4 nm. In particular, the Pt nanoparticle with a mean size of 2.5 nm exhibited the highest catalytic activity with a turnover frequency value of 242.3 ± 7.1 (Formula presented.) mol_Pt⁻¹ min⁻¹ for hydrogen generation from the hydrolysis of AB at 25°C. The size-dependent activity of Pt nanoparticles was attributed to be geometric in nature, primarily due to the square face Pt atoms as the dominant active sites for the hydrolytic dehydrogenation of AB. Novelty Statement: We report size-dependent activity of Pt nanoparticles in the size range of 1 to 4 nm for hydrolytic dehydrogenation of NH₃BH₃. We synthesized five differently sized Pt nanoparticles, which were encapsulated inside dendrimers, with a uniform oxidation state of Pt in an effort to study the intrinsic size effect of Pt nanoparticles on their catalytic activity without masking by heterogeneous oxidation states of Pt catalysts. The five differently sized Pt nanoparticles exhibited significant catalytic activity for the dehydrogenation of NH₃BH₃ under mild conditions.