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

Abstract

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 CO2 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) carbonato complexes with κ1- and κ2-coordination modes. The gradual condensation of mononuclear Pt species in such bicarbonate solutions resulted in the formation of PtO2 nanoparticles aggregating into a solid precipitate on prolonged aging. The deposition of PtO2 particles from bicarbonate solutions was adapted for the preparation of Pt-containing heterogeneous catalysts: bimetallic Pt–Ni catalysts were prepared using various supporting materials (CeO2, SiO2, and g-C3N4) and tested for the activity in hydrazine-hydrate decomposition. All prepared materials showed high selectivity with respect to H2 production from the hydrazine-hydrate with PtNi/CeO2 showing the highest rate of H2 evolution. In the long-range evaluation, the PtNi/CeO2 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-C3N4 catalyst, for the first time, the photodriven decomposition of hydrazine-hydrate was shown to enhance the productivity of the catalyst by 40%.

(Me4N)2[Pt(CO3)2(OH)2]: The Isolated PtIVO6 Carbonato-Complex

“…In the previous studies, we used DFT calculations to confirm the correlation between J( 195 Pt– 13 C) values and the coordination mode of the CO 3 2– ligand and to evaluate the 195 Pt NMR chemical shift values for complexes . These calculations were performed on more than 20 complexes, including dimeric species.…”

“…The prediction of NMR spectra of complexes and spin–spin coupling constants was conducted in the ADF 2022 quantum chemistry computational kit . For this purpose, the general gradient approximation functional BP86 − ,, and the hybrid functional PBE0 , were chosen, as these functionals are used to predict 195 Pt NMR spectra, while the precise of the calculations is of great interest and were not studied properly in previous work related to 195 Pt NMR spectra . TZ2P-J basis set was chosen as it is reliable for the calculations of NMR shifts and spin–spin coupling constants, inter alia for the 195 Pt nuclear resonance .…”

“…In a previous study, we reported on Pt carbonate solutions prepared from platinum­(IV) hydroxide and alkali metal carbonates/bicarbonates or CO 2 in aqueous media . According to NMR-based exploration, accompanied by 13 C isotope enrichment, it was found that a swarm of Pt carbonato-complexes (Figure S1A) is realized in such solutions with both monodentate and bidentate coordination modes of carbonate ligand .…”

“…In a previous study, we reported on Pt carbonate solutions prepared from platinum­(IV) hydroxide and alkali metal carbonates/bicarbonates or CO 2 in aqueous media . According to NMR-based exploration, accompanied by 13 C isotope enrichment, it was found that a swarm of Pt carbonato-complexes (Figure S1A) is realized in such solutions with both monodentate and bidentate coordination modes of carbonate ligand . The resulting solutions have been found to be convenient precursors for depositing of PtO 2 particles, providing a “green” analog for Adam’s process and a noncorrosive alternative of platinum nitrate solutions as a starting material for the heterogeneous catalyst preparation. , …”

Influence of Pt Oxidation State on the Activity and Selectivity of g-C3N4-Based Photocatalysts in H2 Evolution Reaction

“…Due to the spatial separation of charges occurring at the interface between a semiconductor and a metal, or between two different semiconductors, the lifetime of photogenerated electrons and holes increases significantly [35,36]. Platinum and its compounds are most often used as such cocatalysts in photocatalytic hydrogen evolution reactions [37][38][39][40][41][42][43]. It is known that platinum in the metallic state is the most active cocatalyst due to the high Schottky barrier, formed in this case at the metal-semiconductor interface [44].…”