Catalytic acetalization of glycerol to biofuel additives over NiO and Co3O4 supported oxide catalysts: experimental results and theoretical calculations

Catalytic Performances of the Nano FeCo Solids for Biofuel Additives Production: Incorporation of Promoter Effects on the Stability of the Catalysts

“…In the case of aldehydes, more carbonyl groups of the butyraldehyde and furfuraldehyde are activated at temperatures higher than 50 °C, and thus the solid exhibits greater activity at moderate temperatures, in agreement with the literature. ,− Hence, it is necessary to have an activation energy to reduce the intermolecular association of the compounds to have a dispersive adsorption and avoid clustering of the aldehydes by hydrogen bonds around the Mn sites.…”

“…From the previous results, the best glycerol conversions are detected using furfuraldehyde and benzaldehyde as substrates. Although the rate-determining step of the reaction is the carbonium ion formation, , the steric crowding factor does not prevent the acetalization reaction since the reactivity of the catalysts plays a crucial role in the reaction occurrence. This is in agreement with the use of fufuraldehyde as a substrate for acetalization of alcohols .…”

“…Although controversy still continues as to whether cyclic aldehydes exhibit greater steric hindrance in comparison with linear compounds, e.g., acetone and butyraldehyde, the conversion of glycerol with the linear compounds is widely accepted to be higher than acetone or butyraldehyde. , Comparison of the catalytic performances using acetone as a substrate for the acetalization reaction allows the conclusion that acetone behaves simultaneously as a substrate and a solvent owing to the equimolar amounts used. ,, Therefore, glycerol solutions are diluted, resulting in a competition between acetone and glycerol for the active Fe 3+ and Co 3+ /Co 2+ Lewis centers, and less contact between the acetone reagent and the catalyst may occur. This, in turn, gives much lower catalytic performances from solids using acetone as substrates than any aldehyde.…”

“…In particular, the acetalization of glycerol in the presence of aldehydes and ketones (Figure ) produces valuable biofuel additives. − To date, good activities of iron-based catalysts in the acetalization reaction have aroused great interest among researchers. , Although acid–base catalysts have been considered the most effective materials in glycerol valorization reactions, the use of Fe-based catalysts in the acetalization of glycerol reaction is still restricted by issues related to low stability and, with almost all solids, leaching of the active sites. Nanosized Fe-based catalysts can represent alternative and suitable materials to be used in the reaction due to their chemical stability and leaching of the active sites resistance, which is why they have already been exploited for Fe complexes, oxides, and salts. ,, …”