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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 effect 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.

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In this work, the precipitation kinetics of gypsum was studied over a wide range of degree of supersaturation at 25 °C in the reaction Na 2 SO 4(aq) + CaCl 2(aq) + 2 H 2 O → 2 NaCl (aq) + CaSO 4 ⋅ 2 H 2 O (S) with the aim of constructing a comprehensive kinetic model for CaSO 4 •2H 2 O (s) formation that is valid from the lowest (0.04 M) to the highest (0.20 M) feasible initial reactant concentration. To monitor the variation of reactant concentrations during the precipitation reaction, conductometry was employed. For reasonably slow reactions (where the establishment of the equilibrium potential on the indicator electrode was possible), the measurements were supplemented by a Ca-ion-selective electrode. The structure and morphology of the precipitating solids was characterized by XRD and SEM. The induction period was found to decrease about two orders of magnitude with the increasing reactant concentration. It was experimentally established that the influence of the so-called wall effect is of secondary importance. Using the data collected, a kinetic model have been suggested that can describe the entire precipitation process of gypsum simultaneously, incorporating nucleation and crystal growth, in a wide concentration range. Our calculations strongly suggest that the inclusion of the CaSO 4(aq) ion pair is necessary for the appropriate kinetic description of gypsum precipitation.

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In hydrometallurgical processing and acidic wastewater treatment, one of the neutralizing agents employed is MgO or Mg(OH)2. At the end of this process, the resulting solution, which is rich in SO42− and Mg2+ is treated with lime to remove (or minimize the amount) of these ions via the precipitation of Mg(OH)2 and CaSO4·2H2O (gypsum). In our work, an attempt was made to separate the two solids by increasing the induction time of the gypsum precipitation, thus regenerating relatively pure Mg(OH)2 which could be reused in wastewater treatments or hydrometallurgical processing circuits, and in this way, significantly enhancing the economic viability of the process. During our experiments, the reaction of an MgSO4 solution with milk of lime prepared from quicklime was studied. The effects of a range of organic additives, which can slow down the precipitation of gypsum have been assessed. The process was optimized for the most promising inhibiting agent—that is, the citrate ion. The reactions were continuously monitored in situ by conductometric measurements with parallel monitoring of solution pH and temperature. ICP-OES measurements were also carried out on samples taken from the reaction slurry. The composition of the precipitating solids at different reaction times was established by powder XRD and their morphology by SEM. Finally, experiments were carried out to locate the additive after the completion of the precipitation reaction to get information about its potential reuse.

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Effective oxidative transformation of toluene into valuable products was achieved under solvent-free reaction conditions with as-prepared nickel nanoparticles as heterogeneous catalysts in liquid phase. The crystalline structure and size of the asprepared nanoparticles were confirmed by X-ray diffractometry (XRD) and dynamic light scattering (DLS). The catalytic implications of the different crystalline forms (face-centred cubic: fcc; hexagonal close-packed: hcp) of these nanocatalysts were investigated. The product selectivity of toluene oxidation was found to vary depending on the crystalline forms of the catalyst. Fcc nanocatalysts showed remarkable chemoselectivity (83 mol %) for the product benzyl alcohol and were readily reusable. In contrast, the hcp Ni phase showed reasonable reusability but lower chemoselectivity (29 mol %) compared to its fcc counterpart. Moreover, the simple organic solvents used had a remarkable effect on the crystal structure and phase purity of the Ni nanocrystals, which also affected the catalytic process.