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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.

Estudos de química prebiótica demonstram que os minerais podem ter desempenhado um papel importante na proteção, concentração epolimerização de biomoléculas, e entender como se deu a origem da vida é de interesse global. Neste trabalho é investigada a adsorção doíon tiocianato em ferrihidrita, um mineral oxihidróxidopresente na Terra primitiva. No estudo da cinética de adsorção,os dados indicam melhores resultados para o modelo cinético de pseudo-segundaordem e valores de energia de ativação entre o processo de adsorção química e física.Os dados termodinêmicos obtidos através da modelagem de isotermas indica que o processo de adsorção não é favorável, pois é observado um processo endotérmico e de entropia negativa. A alta adsorção de sulfato, cálcio e magnésio mostra que os íons de água do mar podem atuar como agentes de difusão, favorecendo que o tiocianato chegue na superfície da ferrihidrita, criando um enorme complexo de esfera externa. Os dados de FTIR-ATRnão exibiram diferença de estiramento de C≡N comparado com íons de tiocianato adsorvidos e livres, corroborandoa hipótese da formação de complexos de esfera externa. Os resultados do estudo demonstram, portanto, a importância da composição da água do mar 4.0 Ga para o processo adsorção e pré-concentração de moléculas. Studies of prebiotic chemistry have shown that minerals may have played an important role in the protection, concentration, and polymerization of biomolecules, and understanding how the origin of life originated is of global concern. In this work the adsorption of the thiocyanate ion in ferrihydrite, a mineral oxyhydroxide present in the primitive Earth, is investigated. In the study of adsorption kinetics, the data indicate better results for the kinetic model of pseudo-second order and activation energy values between the chemical and physical adsorption process. The thermodynamic data obtained through isothermal modeling indicates that the adsorption process is not favorable, since an endothermic and negative entropy process is observed. The high adsorption of sulfate, calcium and magnesium shows that seawater ions can act as diffusion agents, favoring thiocyanate reaching the surface of the ferrihydrite, creating an enormous outer sphere complex. The FTIR-ATR data did not exhibit C≡N stretching difference compared to adsorbed and free thiocyanate ions, corroborating the hypothesis of the formation of outer sphere complexes. The results of the study demonstrate, therefore, the importance of the composition of seawater 4.0 Ga for the process adsorption and preconcentration of molecules.