Search

Sn–Al-MCM-41 oxide catalysts were synthesized, characterized, and used in glycerol etherification reaction with benzaldehyde. The materials obtained offered heterogeneous Lewis and Bronsted acid sites. The direct functionalization of glycerol with benzaldehyde formed cyclic acetals of high commercial value. The best reaction conditions pointed to a conversion up to 95% of glycerol and final yield of cyclic acetals up to 75%, at a temperature of 120 °C and 240 min using Sn25 catalyst. Moreover, 2-phenyl-1,3-dioxan-5-ol (6-membered cyclic ring) was the most observed products, in cis and trans isomer forms with values above 70%. The temperature presented a positive effect, increasing the glycerol conversion but favored the formation of undesired molecules, such as benzoic acid and benzyl alcohol. The reaction equilibria shifted, due to the high concentration of benzaldehyde, which was useful for a higher yield of cyclic acetals. Time was an important reaction variable, as the selectivity to cyclic acetals may change significantly according to reaction time.

The most crucial role played by minerals was in the preconcentration of biomolecules or precursors of biomolecules in prebiotic seas. If this step had not occurred, molecular evolution would not have occurred. Thiocyanate is an important molecule in the formation of biomolecules as well as a catalyst for prebiotic reactions. The adsorption of thiocyanate onto ferrihydrite was carried out under pH and ion composition conditions in seawater that resembled those of prebiotic Earth. The seawater used in this work had high Mg2+, Ca2+ and SO42− concentrations. The most important result of this work was that ferrihydrite adsorbed thiocyanateata pH value (7.2 ± 0.2) that usually does not adsorb thiocyanate. The high adsorptivity of Mg2+, Ca2+ and SO42−onto ferrihydrite showed that seawater ions can act as carriers of thiocyanate to the ferrihydrite surface, creating a huge outer-sphere complex. Kinetic adsorption and isotherm experiments showed the best fit for the pseudo-second-order model and an activation energy of 23.8 kJ mol−1forthe Langmuir-Freundlich model, respectively. Thermodynamic data showed positive ΔG values, which apparently contradict the adsorption isotherm data and kinetic data that was obtained. The adsorption of thiocyanate onto ferrihydrite could be explained by coupling with the exergonic SO42− adsorption onto ferrihydrite. The FTIR spectra showed no difference between the C≡N stretching peaks of adsorbed thiocyanate and free thiocyanate, corroborating the formation of an outer-sphere complex. All the results demonstrated the importance of the artificial seawater composition for the adsorption of thiocyanate and for understanding prebiotic chemistry.