Platinum(IV) Carbonato Complexes: Formation via the Addition of CO 2 to the [Pt(OH) 6 ] 2- Anion and Generation of Platinum(IV) Oxide Nanoparticles for the Preparation of Catalysts.

A combination of multinuclear nuclear magnetic resonance spectroscopy and theoretical calculation based on density functional theory was used for a speciation study of Pt in solutions prepared either by the interaction of [Pt(OH) 6 ] 2- with gaseous CO 2 in an alkaline solution of platinum(IV) hydroxide ([Pt(OH) 4 (H 2 O) 2 ]) or by the dissolution of [Pt(OH) 4 (H 2 O) 2 ] in an aqueous KHCO 3 solution. The formed solutions contained coexisting Pt(IV) carbonato complexes with κ 1 - and κ 2 -coordination modes. The gradual condensation of mononuclear Pt species in such bicarbonate solutions resulted in the formation of PtO 2 nanoparticles aggregating into a solid precipitate on prolonged aging. The deposition of PtO 2 particles from bicarbonate solutions was adapted for the preparation of Pt-containing heterogeneous catalysts: bimetallic Pt-Ni catalysts were prepared using various supporting materials (CeO 2 , SiO 2 , and g-C 3 N 4 ) and tested for the activity in hydrazine-hydrate decomposition. All prepared materials showed high selectivity with respect to H 2 production from the hydrazine-hydrate with PtNi/CeO 2 showing the highest rate of H 2 evolution. In the long-range evaluation, the PtNi/CeO 2 catalyst operating at 50 °C showed an exceptional turnover number value of 4600 producing hydrogen at a 97% selectivity level and with a mean turnover frequency value of about 470 h -1 . In the case of the PtNi/g-C 3 N 4 catalyst, for the first time, the photodriven decomposition of hydrazine-hydrate was shown to enhance the productivity of the catalyst by 40%.