Solvent effect on the kinetics of benzyl alcohol oxidation on ZnO/MnCO3 catalysts

ZELIN, JUAN; DUARTE, HERNÁN ANTONIO; LUGGREN, PABLO JORGE; SAD, MARÍA EUGENIA; DÍEZ, VERÓNICA KARINA; DI COSIMO, JUANA ISABEL

Buenos Aires

Congreso; 11th WORLD CONGRESS OF CHEMICAL ENGINEERING (WCCE11); 2023

World Chemical Engineering Council (WCEC)

Most of the heterogeneous catalytic processes to obtain fine chemicals involve the use of solvents that fulfill the function of solubilizing reactants and products, facilitating heat transfer, and controlling reactant conversion rates. Thus, its selection is critical, since it can influence the productivity of the processes by modifying catalytic activity and/or selectivity. Previously, we have investigated the oxidation of benzyl alcohol (BA) to benzaldehyde (B) using Zn and Mnbased catalysts with different Zn contents, O2 as oxidant and toluene as solvent. The highest B yield (88%) was achieved on 15.4Zn/MnCO3 catalyst (Zn content=15.4 wt.%). In this work, the relationship between solvent physicochemical properties and catalytic activity of 15.4Zn/MnCO3 catalyst during oxidation of BA were studied. The solvents were selected trying to cover a wide range of physicochemical properties and were evaluated taking into account O2 solubility and reactant (BA)-solvent and catalyst-solvent interactions. Thus, polar aprotic solvents (dibutyl ether, dioxane, dibenzyl ether, dimethyl sulfoxide) and non-polar solvents (heptane, toluene, ethyl benzene) were used (Figure 1). Solvent nature had a significant effect on the initial BA conversion rate. The following activity order was obtained: ethyl benzene (ETB) > toluene (TOL) > dibenzyl ether (DBE) > heptane (HEP) ≈ dioxane (DIO) > dibutyl ether (DBU) = dimethyl sulfoxide (DMS). In order to explain the activity order obtained, physical parameters, solvatochromic scale and adsorption enthalpies (Hads) of solvents on the catalyst surface were analyzed. The solubility of O2 did not show a correlation with the catalytic activity. Regarding the catalyst-solvent interaction, the Hads values resulted low for the solvents investigated. This indicate that catalyst-solvent interaction is weak and it does not significantly affect the catalytic activity. The BA-solvent interaction was described by solvatochromic parameters such as the basicity index (SB) or the polarity/polarizability parameters (* and ET(30)).Initial BA oxidation rate increased with * and ET(30) for both polar and non-polar solvents. This can be attributed to the electrostatic stabilization of the activated complex by the solvent. Thus, activity is mainly governed by the reactant-solvent interaction. Solvents that showed better kinetic performance exhibited intermediate BA-solvent interactions, such as non-polar aromatic solvents ethylbenzene and toluene.