The cleavage of the etheric C–O bond in diphenyl ether (DPE), phenethyl phenyl ether (PPE) and benzyl-phenyl ether (BPE) has been investigated by using Ru/C (5% wt) and Pd/C (5% wt), as heterogeneous catalysts, under reaction conditions generally adopted for the reductive catalytic fractionalization of lignocellulosic biomasses (lignin-first approach). Catalytic tests were carried out in the presence of simple C1-C3 alcoholic H-donor solvents (methanol, ethanol and 2-propanol) used as such or in mixture with water in the temperature range of 120–240 °C both in the presence or in the absence of molecular hydrogen as reducing agent. Under transfer hydrogenolysis conditions, the Ru/C catalyst was found to be the best performing system in the cleavage of the 4–O–5 etheric C–O bond (95 % DPE conversion in 2-propanol at 210 °C after 3 h of reaction) with a less pronounced tendency in hydrogenating the aromatic ring. Upon increasing the water content in the reaction medium, a decrease in the cleavage of the C–O bond of DPE together with a higher production of phenolics is observed as a consequence of the reductive hydrolysis reaction occurrence. The best yield in aromatic compounds (52 %) was obtained by using as solvent a water/2-propanol (75:25, v/v) mixture in absence of added molecular hydrogen, with the alcoholic fraction being the in-situ H-source. A lower tendency to undergo to hydrolysis reaction together with a higher production of aromatics is registered in the case of phenethyl phenyl ether and benzyl-phenyl ether. Results are explained in terms of the higher steric hindrance of PPE and BPE with respect to DPE and of the competitive adsorption of arenes arising from hydrogenolysis of etheric β–O–4 and α–O–4 bonds (phenol + ethyl benzene or phenol + toluene) on the Ru/C catalyst surface.

Hydrogenolysis of aromatic ethers under lignin-first conditions

Paone E.;Beneduci A.;
2020

Abstract

The cleavage of the etheric C–O bond in diphenyl ether (DPE), phenethyl phenyl ether (PPE) and benzyl-phenyl ether (BPE) has been investigated by using Ru/C (5% wt) and Pd/C (5% wt), as heterogeneous catalysts, under reaction conditions generally adopted for the reductive catalytic fractionalization of lignocellulosic biomasses (lignin-first approach). Catalytic tests were carried out in the presence of simple C1-C3 alcoholic H-donor solvents (methanol, ethanol and 2-propanol) used as such or in mixture with water in the temperature range of 120–240 °C both in the presence or in the absence of molecular hydrogen as reducing agent. Under transfer hydrogenolysis conditions, the Ru/C catalyst was found to be the best performing system in the cleavage of the 4–O–5 etheric C–O bond (95 % DPE conversion in 2-propanol at 210 °C after 3 h of reaction) with a less pronounced tendency in hydrogenating the aromatic ring. Upon increasing the water content in the reaction medium, a decrease in the cleavage of the C–O bond of DPE together with a higher production of phenolics is observed as a consequence of the reductive hydrolysis reaction occurrence. The best yield in aromatic compounds (52 %) was obtained by using as solvent a water/2-propanol (75:25, v/v) mixture in absence of added molecular hydrogen, with the alcoholic fraction being the in-situ H-source. A lower tendency to undergo to hydrolysis reaction together with a higher production of aromatics is registered in the case of phenethyl phenyl ether and benzyl-phenyl ether. Results are explained in terms of the higher steric hindrance of PPE and BPE with respect to DPE and of the competitive adsorption of arenes arising from hydrogenolysis of etheric β–O–4 and α–O–4 bonds (phenol + ethyl benzene or phenol + toluene) on the Ru/C catalyst surface.
Benzyl phenyl ether
Catalytic transfer hydrogenolysis
Diphenyl ether
Heterogeneous catalysis
Hydrogenolysis
Hydrolysis
Lignin
Lignin depolymerization
Lignin-first biorefinery
Lignocellulosic biomasses
Palladium
Phenethyl phenyl ether
Reductive catalytic fractionalization
Ruthenium
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11770/309731
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