Cerium(III) Nitrate Derived CeO 2 Support Stabilising PtO x Active Species for Room Temperature CO Oxidation

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

The first fully inorganic Pt(IV) carbonato-complex trans-[Pt(CO3)2(OH)2]2- with a {PtO6} coordination sphere was isolated as the (Me4N)2[Pt(CO3)2(OH)2] (1) salt. The compound 1 was characterized using single-crystal and powder X-ray diffraction, Raman spectroscopy, infrared spectroscopy (FTIR), electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance spectroscopy (NMR), and thermogravimetric analysis (TG). Density functional theory (DFT) calculations were also performed to analyze the spectral features of the complex. 1 crystallizes in the triclinic system (P-1) with a Z of 1. The trans-[Pt(CO3)2(OH)2]2- anion has axial hydroxo ligands and κ2-CO3 ligands, which form an equatorial plane. This anionic complex exhibits notable stability in aqueous solutions, while the axial hydroxo ligand can be readily modified, as exemplified by the acylation of the trans-[Pt(CO3)2(OH)2]2- into trans-[Pt(CO3)2(OAc)2]2- anion. Furthermore, it has been shown that rigid and glittering platinum coatings can be electrochemically deposited from an aqueous solution of 1 without the addition of surfactants.

Speciation and separation of platinum(iv) polynuclear complexes in concentrated nitric acid solutions

Understanding the solution chemistry of Pt(iv) is crucial for the hydrometallurgy of precious metals. To gain such an understanding, the speciation and separation of Pt(iv) complexes in concentrated HNO₃ solutions were investigated via Pt L_III edge X-ray absorption fine structure (XAFS) spectroscopy. The XAFS results for concentrated HNO₃ solutions of Na₂Pt(OH)₆ revealed the dominant presence of Pt polynuclear complexes, wherein the formation of Pt(iv) polynuclear complexes depended on the metal concentration and the Na₂Pt(OH)₆ dissolution temperature. The dominant species present in a heated nitrate solution of 0.90 g-Pt L^-1 and a non-heated nitrate solution of 3.2 g-Pt L^-1 were dinuclear Pt(iv) complexes, whereas those in a heated solution of 3.0 g-Pt L^-1 were predominantly larger polynuclear complexes, such as, tetra- and hexa-nuclear complexes. The presence of larger Pt(iv) complexes was confirmed via XAFS spectroscopy, wherein the adsorption of Pt(iv) ions from a 10 M HNO₃ solution by a chelating resin functionalised with iminodiacetic acid and a strongly basic anion-exchange resin bearing trimethyl ammonium nitrate was examined. The adsorption of 50 mg L^-1 of Pt(iv) by the two resins was tested using aqueous solutions diluted from heated HNO₃ solutions with varying metal concentrations, and also from a non-heated solution. We found that Pt(iv) complexes from heating solutions containing high Pt(iv) concentrations displayed high adsorption percentages. In addition, the selective adsorption of Pt(iv) over Pd(ii), Ag(i), Cu(ii), Ni(ii), and Fe(iii) from a 10 M HNO₃ solution was achieved using a strongly basic anion-exchange resin.

Photoinduced Deposition of Platinum from (Bu4N)2[Pt(NO3)6] for a Low Pt-Loading Pt/TiO2 Hydrogen Photogeneration Catalyst

An efficient method for the deposition of ionic platinum species PtO_x onto a TiO₂ surface was developed on the basis of light-induced activation of the [Pt(NO₃)₆]^2- anion. The deposited PtO_x species with an effective Pt oxidation state between +4 and +2 have an oxygen-made environment and include single ion centers {PtO_n} and polyatomic ensembles {Pt_nO_m} connected to a TiO₂ surface with Pt-O-Ti bonds. The resulting PtO_x/TiO₂ materials were tested as photocatalysts for the hydrogen evolution reaction (HER) from a water ethanol mixture and have shown uniquely high activity with the rate of H₂ evolution achieving 11 mol h^-1 per gram of Pt, which is the highest result for such materials reported to date. A combination of spectral methods shows that, under HER conditions, reduction of the supported PtO_x species leads to the formation of well-dispersed nanoparticles of metallic platinum attached on the surface of TiO₂ by Ti-O-Pt bonds. The high activity of the PtO_x/TiO₂ materials is believed to result from a combination of uniform distribution of small platinum nanoparticles over the titania surface and their close interaction with TiO₂.