Platinum(IV) Carbonato Complexes: Formation via the Addition of CO₂ 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 resonancespectroscopyand theoretical calculation based on density functional theory wasused for a speciation study of Pt in solutions prepared either bythe interaction of [Pt(OH)(6)](2-) with gaseousCO(2) in an alkaline solution of platinum(IV) hydroxide ([Pt(OH)(4)(H2O)(2)]) or by the dissolution of [Pt(OH)(4)(H2O)(2)] in an aqueous KHCO3 solution. The formed solutions contained coexisting Pt(IV) carbonatocomplexes with kappa(1)- and kappa(2)-coordinationmodes. The gradual condensation of mononuclear Pt species in suchbicarbonate solutions resulted in the formation of PtO2 nanoparticles aggregating into a solid precipitate on prolongedaging. The deposition of PtO2 particles from bicarbonatesolutions was adapted for the preparation of Pt-containing heterogeneouscatalysts: bimetallic Pt-Ni catalysts were prepared using varioussupporting materials (CeO2, SiO2, and g-C3N4) and tested for the activity in hydrazine-hydratedecomposition. All prepared materials showed high selectivity withrespect to H-2 production from the hydrazine-hydrate withPtNi/CeO2 showing the highest rate of H-2 evolution.In the long-range evaluation, the PtNi/CeO2 catalyst operatingat 50 degrees C showed an exceptional turnover number value of 4600producing hydrogen at a 97% selectivity level and with a mean turnoverfrequency value of about 470 h(-1). In the case ofthe PtNi/g-C3N4 catalyst, for the first time,the photodriven decomposition of hydrazine-hydrate was shown to enhancethe productivity of the catalyst by 40%. The chemistry of platinum(IV) carbonatocomplexes, generatedeither by the (a) addition of CO2 to the [Pt(OH)(6)](2-) anions (without Pt-O bond breaking)in an alkaline solution or (b) dissolution of platinum(IV) hydroxidein an aqueous carbonate/bicarbonate media is uncovered by Pt-195 and C-13 NMR spectroscopy. Controllable hydrolysis ofthe platinum(IV) carbonato complexes was exhibited as an efficientway to generate the nanoparticles of hydrated PtO2 oxideavoiding corrosive acidic platinum solutions. The hydrolysis processwas thoroughly studied and the applicability of such a phenomenonfor the catalyst's preparative chemistry was illustrated bythe fabrication of the supported Pt-Ni catalysts showing greatproductivity and stability in the process of H-2 generationfrom the hydrazine hydrate.