RESUMO
Supercritical carbon dioxide (SC-CO2)-based approaches have become more popular in recent years as alternative methods for creating micro- or nanosized medicines. Particularly, high drug solubility is required in those techniques using SC-CO2 as a solvent. During the most recent pandemic years, favipiravir and montelukast were two of the most often prescribed medications for the treatment of COVID-19. In this study, ethanol at 1 and 3 mol% was utilized as a cosolvent to increase the solubility of both medicines in SC-CO2 by a static approach using a range of temperatures (308 to 338 K) and pressure (12 to 30 MPa) values. The experimentally determined solubilities of favipiravir and montelukast in SC-CO2 + 3 mol% ethanol showed solubility values up to 33.3 and 24.5 times higher than that obtained for these drugs with only SC-CO2. The highest values were achieved in the pressure of 12 MPa and temperature of 338 K. Last but not least, six density-based semi-empirical models with various adjustable parameters were used to perform the modeling of the solubility of favipiravir and montelukast.
RESUMO
CuO-CeO2/SiO2 catalysts lose activity when they are calcined at 600 °C and temperatures above. This loss of activity was related to a decrease in the amount of highly dispersed Cu species interacting with Ce (CuO-CeO2 interface) over the SiO2 support. These species are highly active in CO oxidation, so this reaction was selected to conduct this study. In order to avoid the activity loss in CuO-CeO2/SiO2 catalysts, the effect of high Ce loads (8, 16, 24, and 36%) on the thermal stability of these catalysts was studied. The results reveal that when increasing calcination temperature from 500 to 700 °C, the catalysts with Ce load equal to or higher than 24% increase the formation of highly dispersed Cu interacting with Ce and therefore the activity (90% of CO conversion at 120 °C). In catalysts with Ce load below 24%, Cu species agglomerate and decrease the activity (less than 5% of CO conversion at 120 °C).
RESUMO
The transient combustion of biomass leads to the evolution of a variety of pollutants (NO, CO, organic compounds, and many others) that can react with each other on a suitable catalyst to generate compounds of lower toxicity. Here, the transient reduction of NO with CO and naphthalene in the presence of oxygen was studied on a Ca/Cu/YCeO2-TiO2 catalyst. Response surface methodology was used to identify the optimum amounts of calcium, copper, and cerium. The optimized Ca/Cu/YCeO2-TiO2 catalyst was then extensively studied and characterized. The coupling of yttrium-stabilized ceria with TiO2 provided an active support that effectively activated naphthalene. When calcium and copper were added to the support, the obtained Ca/Cu/YCeO2-TiO2 catalyst achieved the full conversion of CO and naphthalene and 72% conversion of NO. The Ca/Cu/YCeO2-TiO2 catalyst possessed labile oxygen species, which might be related to the high catalytic activity.
