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The activity and selectivity of catalytic systems are influenced by many important factors, such as the composition of the surface, the size and structure of the active sites, as well as the oxidation state of the active components. In this study, we investigated the nature of the active components in Pt/TiO2catalysts for selective ammonia oxidation upon their modification with copper. Analysis using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed that an increase in copper content led to a significant dispersion of platinum particles due to the formation of subnanoscale Pt(Cu)Oxspecies. Application of temperature-programmed reduction (TPR-H2) and X-ray photoelectron spectroscopy (XPS) techniques provided valuable data on the redox properties of the catalysts. The introduction of copper resulted in a notable increase in the fraction of oxidized platinum. Once reduced, platinum in the composition of the Pt–Cu/TiO2catalysts was easily reoxidized upon subsequent exposure to oxygen already at room temperature. The Pt–Cu/TiO2catalysts comprised oxidized copper species, which demonstrated more labile redox behavior at lower temperatures compared to the Cu/TiO2catalyst. The facilitated redox transitions of the active components contributed to the enhanced selectivity of the Pt–Cu/TiO2samples toward N2by affecting the reaction mechanism. The obtained results provide new insights into key aspects governing the effective oxidation of slip ammonia at low temperatures.

A mixture of rhodium(iii) hydroxocomplexes formed during the polycondensation process in alkaline media has been fully characterized by the hyphenated high performance liquid chromatography with electrospray ionization mass spectrometry (HPLC-ESI-MS). The baseline separation was achieved using reverse phase ion-pair chromatography (RP-IP-HPLC) in gradient elution mode. When using SDS as the ion pair, the formation of all types of its associates with the molecules of acetonitrile, as well as oligomers of rhodium aquahydroxocomplexes, etc.was taken into consideration. As a result, it was shown that the test mixture is presented by [Rh(H2O)6]3+, [Rh2(μ-OH)2(H2O)8]4+, [Rh3(μ-OH)4(H2O)10]5+, [Rh4(μ-OH)6(H2O)12]6+.

X-ray diffraction (XRD) pattern of nanosized equimolar solid solution CoIr prepared by thermolysis of [Co(NH3)6][Ir(C2O4)3] contains peaks characteristic of both face-centered cubic (fcc) and hexagonal close-packed (hcp) structure. Moreover, 101peak of hcp modification is substantially wider than 100and 002peaks, 102and 103are very broad and almost invisible. Peak 200of fcc structure is wider than the other peaks of this modification and slightly shifted toward lower angles. It was shown by simulation of XRD patterns that particles of CoIr alloy are nanoheterogeneous and consist of lamellar domains having fcc and hcp structures. The best fit was obtained for the following model parameters: an average crystallites size is about 10 nm, average thicknesses of the fcc and hcp domains are 1.7 and 1.1 respectively. The presence of domain structure was confirmed by transmission electron microscopy data.

The hydrolysis of [RhCl6]3–in NaOH–water solutions was studied by spectrophotometric methods. The reaction proceeds via successive substitution of chloride with hydroxide to quantitatively form [Rh(OH)6]3–. Ligand substitution kinetics was studied in an aqueous 0.434–1.085 M NaOH matrix in the temperature range 5.5–15.3 °C. Transformation of [RhCl6]3–into [RhCl5(OH)]3–was found to be the rate-determining step with activation parameters of ΔH†= 105 ± 4 kJ mol–1and ΔS†= 59 ± 10 J K–1mol–1. The coordinated hydroxo ligand(s) induces rapid ligand substitution to form [Rh(OH)6]3–. By simulating ligand substitution as a dissociative mechanism, using density functional theory (DFT), we can now explain the relatively fast and slow kinetics of chloride substitution in basic and acidic matrices, respectively. Moreover, the DFT calculated activation energies corroborated experimental data that the kinetic stereochemical sequence of [RhCl6]3–hydrolysis in an acidic solution proceeds as [RhCl6]3–→ [RhCl5(H2O)]2–→ cis-[RhCl4(H2O)2]−. However, DFT calculations predict in a basic solution the trans route of substitution [RhCl6]3–→ [RhCl5(OH)]3–→ trans-[RhCl4(OH)2]3–is kinetically favored.