Ceramics samples with the nominal composition [(ZrO₂)_0.95(Y₂O₃)_0.05]_1-x[PrO_y]_x and praseodymia contents of x = 0.05–0.15 were prepared by the direct firing of compacted 5YSZ + PrO_y mixtures at 1450–1550 °C for 1–9 h and characterized for prospective applicability in reversible solid oxide cells. XRD and SEM/EDS analysis revealed that the dissolution of praseodymium oxide in 5YSZ occurs via the formation of pyrochlore-type Pr₂Zr₂O₇ intermediate. Increasing PrO_y additions results in a larger fraction of low-conducting pyrochlore phase and larger porosity, which limit the total electrical conductivity to 2.0–4.6 S/m at 900 °C and 0.28–0.68 S/m at 700 °C in air. A longer time and higher temperature of firing promotes the phase and microstructural homogenization of the ceramics but with comparatively low effect on density and conductivity. High-temperature processing leads to the prevailing 3+ oxidation state of praseodymium cations in fluorite and pyrochlore structures. The fraction of Pr⁴⁺ at 600–1000 °C in air is ≤2% and is nearly independent of temperature. 5YSZ ceramics with praseodymia additions remain predominantly oxygen ionic conductors, with p-type electronic contribution increasing with Pr content but not exceeding 2% for x = 0.15 at 700–900 °C. The average thermal expansion coefficients of prepared ceramics are in the range of 10.4–10.7 ppm/K.

The present work explores the possibility of incorporation of silicon into the crystal structure of Ruddlesden-Popper La₂NiO_4+δ mixed conducting ceramics with the aim to improve the chemical compatibility with lanthanum silicate-based solid electrolytes. Ceramics with the nominal composition La₂Ni_1−ySi_yO_4+δ (y = 0, 0.02 and 0.05) were prepared by the glycine nitrate combustion technique and sintered at 1450 °C. While minor changes in the lattice parameters of the tetragonal K₂NiF₄-type lattice may suggest incorporation of a small fraction of Si into the Ni sublattice, combined XRD and SEM/EDS studies indicate that this fraction is very limited (≪2 at.%, if any). Instead, additions of silica result in segregation of apatite-type La_10−xSi₆O_26+δ and La₂O₃ secondary phases as confirmed experimentally and supported by the static lattice simulations. Both total electrical conductivity and oxygen-ionic transport in La₂NiO_4+δ ceramics are suppressed by silica additions. The preferential reactivity of silica with lanthanum oxide opens a possibility to improve the compatibility between lanthanum silicate-based solid electrolytes and La₂NiO_4+δ-based electrodes by appropriate surface modifications. The promising potential of this approach is supported by preliminary tests of electrodes infiltrated with lanthanum oxide.

This study presents the synthesis and characterization of mesoporous silica using biobased silica recovered from rice husks (RHs) as an excellent example of the circular economy. Distinct hydrothermal methods were used, namely, the autoclave hydrothermal method and microwave irradiation. Furthermore, the microwave-synthesized SBA-15 material was subjected to post-functionalization with –SO₃H groups using the organosilane 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS). The structural and chemical properties of the prepared materials were rigorously characterized through several techniques, thereby confirming the successful preparation of this functionalized material. Subsequently, the functionalized SBA-15 (CSPTMS@SBA-15) was employed as a catalyst in the synthesis of ethyl levulinate (EL) from 5-hydroxymethylfurfural (5-HMF) using different methodologies: typical high-pressure batch reactor, conventional heating, and microwave irradiation. This investigation aimed to elucidate the influence of microwave and non-microwave heating methods on the efficient conversion of 5-HMF into EL. The findings revealed that the microwave reactor exhibited superior conversion rates and selectivity when compared to the non-microwave heating methods. The study also explored the effects of temperature and utilization of various alcohols as both solvents and reagents. The results demonstrated that higher temperatures favored the production of alkyl levulinate and that complete conversion of 5-HMF was attainable for all the alcohols employed. Specifically, for methanol and ethanol a 100% yield of alkyl levulinates was achieved, while for 1-propanol and butanol a reduction in the yield of alkyl levulinates was observed. These outcomes underscore the feasibility of achieving significant yields of various alkyl levulinates through the utilization of CSPTMS@SBA-15 as a catalyst.