Niobium Oxides as Heterogeneous Catalysts for Biginelli Multicomponent Reaction.

This study reports a simple, reusable, and recoverable niobium-based heterogeneous catalysts for Biginelli multicomponent reactions. Different methods of catalysts preparation were investigated. For this purpose, HY-340 (Nb2O5·nH2O) and Nb2O5 were chemically and/or thermally treated and investigated as catalysts for dihydropyrimidinones (DHPMs) production. The catalysts were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, temperature-programmed desorption of NH3, adsorption/desorption of N2 at -196 °C, and thermogravimetric and differential thermal analysis. The characterization results showed that niobium oxides have the potential to be used as catalysts because of high crystallinity and large surface area. Among the tested catalysts, Nb2O5 chemically treated (Nb2O5/T) showed the best catalytic performance. In the absence of solvents, 94% yield of DHPMs was achieved. Also, Nb2O5/T can be reused three times without a significant yield decrease. Additionally, a feasible reaction pathway was suggested based on the Knoevenagel mechanism for DHPM synthesis using niobium-based catalysts.

Simultaneous recycling of waste solar panels and treatment of persistent organic compounds via supercritical water technology.

The study addresses the application of the supercritical water technology in the simultaneous recycling of obsolete solar panels and treatment of persistent organic compounds. The obsolete solar panels samples were characterized by TEM-EDS, SEM, TG-DTA, XRD, WDXRF, MP-AES and elemental analysis. Initially, the optimized parameters for the degradation of solid organic polymers present in residual solar panels via oxidation in supercritical water were defined by an experimental design. Under optimized conditions, 550 °C, reaction time of 60 min, volumetric flow rate of 10 mL min-1 and hydrogen peroxide as oxidant agent, real laboratory liquid wastewater was used as feed solution to achieve 99.6% of polymers degradation. After the reaction, the solid product free of organic matter was recovered and characterized. On average, a metal recovery efficiency of 76% was observed. Metals such as aluminum, magnesium, copper, and silver, that make up most of the metallic fraction, were identified. Only H2, N2 and CO2 were observed in the gaseous fraction. Then, initial data on the treatment of the liquid decomposition by-products, generated during ScW processing, were reported. A total organic carbon reduction of 99.9% was achieved after the subsequential treatment via supercritical water oxidation using the same experimental apparatus. Finally, insights on the scale-up, energy integration and implementation costs of a ScW solid processing industrial unit were presented using the Aspen Plus V9 software.