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Catalysts 11(5), 617 (1-13) (2021). doi:10.3390/catal11050617 special issue: "Present Challenges in Catalytic Emission Control for Internal Combustion Engines", Despite their high atomic dispersion, single site catalysts with Pt supported on CeO$_2$ were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO$_2$ single site catalyst under more complex gas mixtures, including CO, C$_3$H$_6$ and CO/C$_3$H$_6$ oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt$^{4+}$ to Pt$^{2+}$ due to the increase of temperature, CO adsorbs and reduces Pt$^{2+}$ to Pt$^{δ+}$ and assists its migration with final formation of Pt$_{x}$$^{Δ+}$ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria., Published by MDPI, Basel

The temporary storage of oxygen in a solid catalyst is imperative for many important industrial oxidation reactions in the gas phase, for instance the post-treatment of automotive exhaust gas. CeO2 is a promising catalyst for the HCl oxidation (Deacon process) in order to recover Cl2. Employing shape- controlled CeO2 nanoparticles (cubes, octahedrons, rods) with facets of preferential orientations ((100), (111), (110)), we studied the activity and stability under two reaction conditions (harsh: Ar:HCl:O2 = 6:2:2 and mild: Ar:HCl:O2 = 7:1:2). It turns out that both activity and stability are structure sensitive. In terms of space time yield (STY), the rods are the most active particles, followed by the cubes and finally the octahedrons. Ceria also possesses high OSC (oxygen storage capacity) which is a measure of the oxygen quantity that material can store and release. This makes ceria suitable for redox reactions which usually follow Mars-van Krevelen mechanism (surface oxygen atoms directly involved in reactions). A peculiar mixed Ce-Zr (1:1) oxide, the ordered κ-phase, is a promising catalytic material exhibiting an extraordinarily high oxygen storage capacity (OSC) and high thermal and chemical stability. We elucidate the temperature-dependent transformation between the pyrochlore pyr-Ce2Zr2O7.3 and κCe2Zr2O8 phase upon oxygen uptake by in-situ X-ray diffraction, X-ray absorption and in-situ Raman spectroscopy, providing insights into the electronic and structural changes on the atomic level, which are at the heart of the extraordinarily high OSC. We demonstrate that the Ce3+ concentration can be followed during transformation in-situ by Raman spectroscopy of the electronic spin flip in the f-shell of Ce3+. The catalytic activity of the κ-Ce2Zr2O8 phase has been investigated without an additional active component such as Pt: While the high OSC of the kappa phase is beneficial for the oxidation of CO, the oxidation of HCl turns out to be not affected by the high OSC.

The temporary storage of oxygen in a solid catalyst is imperative for many important industrial oxidation reactions in the gas phase, for instance the post-treatment of automotive exhaust gas. A peculiar mixed Ce–Zr (1:1) oxide, the ordered κ-Ce2Zr2O8 phase, is a promising catalytic material exhibiting an extraordinarily high oxygen storage capacity (OSC) and high thermal and chemical stability. We elucidate the temperature-dependent transformation between the pyrochlore pyr- Ce2Zr2O7 and κ-Ce2Zr2O8 phase upon oxygen uptake by in situ X-ray diffraction, X-ray absorption, and in situ Raman spectroscopy, providing insights into the electronic and structural changes on the atomic level, which are at the heart of the extraordinarily high OSC. We demonstrate that the Ce3+ concentration can be followed during transformation in situ by Raman spectroscopy of the electronic spin flip in the f-shell of Ce3+. The catalytic activity of the κ-Ce2Zr2O8 phase was investigated without an additional active component such as noble metals (Pt, etc.). While the high OSC of the κ-phase is beneficial for the oxidation of CO, the oxidation of HCl turns out to be unaffected by the high OSC.

Temporary storage of oxygen in a solid catalyst is imperative for many important industrial oxidation reactions in the gas phase, for instance the post-treatment of automotive exhaust gas. A peculiar mixed Ce–Zr (1:1) oxide, the ordered κ-Ce2Zr2O8 phase, is a promising catalytic material exhibiting an extraordinarily high oxygen storage capacity (OSC) and high thermal and chemical stability. We elucidate the temperature-dependent transformation between the pyrochlore pyr- Ce2Zr2O7 and κ-Ce2Zr2O8 phase upon oxygen uptake by in situ X-ray diffraction, X-ray absorption, and in situ Raman spectroscopy, providing insights into the electronic and structural changes on the atomic level, which are at the heart of the extraordinarily high OSC. We demonstrate that the Ce3+ concentration can be followed during transformation in situ by Raman spectroscopy of the electronic spin flip in the f-shell of Ce3+. The catalytic activity of the κ-Ce2Zr2O8 phase was investigated without an additional active component such as noble metals (Pt, etc.). While the high OSC of the κ-phase is beneficial for the oxidation of CO, the oxidation of HCl turns out to be unaffected by the high OSC.

The temporary storage of oxygen in a solid catalyst is imperative for many important industrial oxidation reactions in the gas phase, for instance the post-treatment of automotive exhaust gas. A peculiar mixed Ce-Zr (1:1) oxide, the ordered -Ce2Zr2O8 phase, is a promising catalytic material exhibiting an extraordinarily high oxygen storage capacity (OSC) and high thermal and chemical stability. We elucidated the temperature-dependent transformation between the pyrochlore pyr- Ce2Zr2O7.3 and -Ce2Zr2O8 phase upon oxygen uptake by in-situ X-ray diffraction, X-ray absorption and in-situ Raman spectroscopy, providing insights into the electronic and structural changes on the atomic level, which are at the heart of the extraordinarily high OSC. We demonstrate that the Ce3+ concentration can be followed during transformation in-situ by Raman spectroscopy of the electronic spin flip in the f-shell of Ce3+. The catalytic activity of the k-Ce2Zr2O8 phase has been investigated without an additional active component such as Pt: While the high OSC of the kappa phase is beneficial for the oxidation of CO, the oxidation of HCl turns out to be not affected by the high OSC.

In this PhD thesis, several inorganic nanostructures were synthesized through a wetchemistry synthetic route. In particular, the miniemulsion approach was exploited to induce the formation in confined space of pure and doped binary (oxides, sulfides and fluorides) and ternary (hydroxides) compounds, of metal/oxide nanocomposites and of hybrid organic/inorganic nanoparticles. Through this methodology, the investigated systems were obtained in crystalline form already at room temperature. Various miniemulsion formulations were used to control the size and morphology of the investigated systems, achieving different emulsion stabilities and yields of crystalline powders. The obtained materials were thoroughly characterized through a wide array of techniques from the compositional, structural and functional points of view. In particular, XRD (X-Ray Diffraction) was employed to assess the formation of crystalline materials and to calculate average crystallite sizes (through Rietveld refinement), and the data thus obtained were compared with micrographs collected through TEM (Transmission Electron Microscopy). This latter microscopy, coupled with SEM (Scanning Electron Microscopy), was also used to investigate the morphology of the synthesized nanostructures. In addition, the surface composition was explored through XPS (X-ray Photoelectron Spectroscopy) and, especially in the case of systems doped with transition metal or lanthanide ions, atomic ratios were compared to those obtained through ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) or ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) allowed to evaluate the presence and amount of residual surfactant moieties adsorbed on the materials surfaces. In the case of the doped systems, XAS (X-ray Absorption Spectroscopy) measurements were performed in order to study in detail the local structure of the doping ions, also with respect to the hosting matrices. The obtained data were further correlated to the photoluminescence properties. These materials, also due to the biocompatibility of the selected matrices, might indeed be potentially applied for optical bioimaging. At this regard, cytotoxicity and cell viability assays were also performed on selected systems.