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Efficient Lewis-acid-catalyzed direct conversion of aldehydes to 1, 2-diketones in the liquid phase was enabled by using newly designed and developed ceria–zirconia-based high-entropy oxides (HEOs) as the actual catalysts. The synergistic eàect of various cations incorporated in the same oxide structure (framework) was partially responsible for the efficiency of multicationic materials compared to the corresponding single cation oxide forms. Furthermore, a clear, linear relationship between the Lewis acidity and the catalytic activity of the HEOs was observed. Due to the developed strategy, exclusively diketone- selective, recyclable, versatile heterogeneous catalytic transformation of aldehydes can be realized under mild reaction conditions.

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.

Specific structure of perovskite compounds provides them with various interesting magnetic, dielectric and optical properties. It has become very trendy to alter particle size instead of altering chemical composition since the properties of materials have appeared to be size- and shape-dependent. Triple Sr3Fe2WO9 perovskite has been prepared in form of semi- spherical particle agglomerates using a modified aqueous sol–gel citrate route. Synthesis mechanism and redox properties of precursor metal salts in aqueous solution have been studied by electrochemical measurements and UV/VIS absorbance spectros-copy where it has been observed that Fe3+ is stable after coordination with ammonia molecules . Structural investigation has been conducted by ambient and in situ X-ray powder diffraction (XPRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) and unpolarized Raman spectroscopy and it has been observed that synthesized compound crystalizes in tetragonal system (space group I4/m) with crystallite size of 36 nm and high crystallinity and fully transforms into desired perovskite compound at 1273 К. Magnetic properties have been determined using SQUID measurements and have shown ferrimagnetic ordering at 373 K. Dielectric properties have revealed a proportional increase of dielectric constant with temperature and reverse proportional decrease with frequency. Optical properties have been estimated using Tauc method which revealed band gap values of 2.71 еV for direct band gap and 2.10 eV for indirect band gap. Authors acknowledge Croatian Science Foundation (IP-2016-06-3115) for full financial support.

Specific structure of perovskite compounds provides them with various interesting properties which vary from magnetic and electric properties to magnetic frustration and half-metallicity. Since it is hard to stabilize Mn3+ cation in solid form, it is important to use solution chemistry methods. Sr3Mn2(W/Te)O9 triple perovskites have been prepared by means of hydrothermal method with sodium hydroxide as mineralizer and ethanol as buffering agent. Since the high spin 6-coordinated Mn3+ cation and Fe3+ cation have the same values of ionic radius (0.645 Å), it is reasonable to expect similar structure of Sr3Mn2(W/Te)O9 and corresponding Sr3Fe2(W/Te)O9 compounds [1, 2]. It is important to find suitable synthesis route for stabilization of desired oxidation state of transition metal cation. Stabilization of cations in solution and synthesized compounds itself have been investigated by electrochemical measurements. Structural characterization has been done by X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA) and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. Similar research has already been done with tellurium- and tungsten- based perovskites. In this research the advances of solution chemistry methods (bottom up approach), over the solid state routes towards the synthesis of complex perovskite structures will be presented.

Specific structure of perovskite compounds provides them with various interesting properties which vary from magnetic and electric properties to magnetic frustration and half-metallicity. Double A2Ni(Te, W)O6 and triple A3(Fe, Co)2(W/Te)O9 (A=Sr, Ba) perovskites have been prepared in nanocrystalline form using a modified aqueous sol–gel citrate route. Solution chemistry synthesis mechanism and synthesized compounds itself have been studied by electrochemical measurements. Structural investigation has been conducted by ambient and in situ X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA) and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. Similar research has already been done with tellurium- and tungsten- based perovskites. In this research the advances of solution chemistry methods (bottom up approach), namely sol-gel citrate route, over the solid-state routes towards the synthesis of complex perovskite structures will be presented.

Perovskite materials exhibit interesting physical properties due to their exceptional structure. Those properties have been studied for various practical applications: from superconductors, electrode and electrolyte materials for fuel cells, catalytic converters in diesel vehicles, components for solar cells to the memory device components. While numerous metal oxide combinations with single, double and triple perovskite structure have been characterized so far, only few of them have been synthesized in nanocrystalline form. Since nanosized materials have exceptional properties due to the quantum size effect, nanocrystalline perovskites could possess interesting properties. Hereby we present nanocrystalline A3B2(W/Te)O9 and A2B(W/Te)O6 (A=Sr, Ba, Ca ; B=Fe, Co, Mn, Ni) with double and triple perovskite structure that have been synthesized using bottom up approach in liquid state. We investigated reaction mechanisms of synthetic routes, structurally characterizied synthesized compounds and measured their properties in comparison with corresponding bulk materials.