Transfer Hydrogenation of Methyl and Ethyl Levulinate Promoted by a ZrO2 Catalyst: Comparison of Batch vs Continuous Gas-Flow Conditions

The catalytic conversion of methyl and ethyl levulinates into \u3b3-valerolactone (GVL) by using methanol, ethanol, and 2- propanol as the H-donor/solvent, promoted by the ZrO2 catalyst, is described as carried out under both batch and gas-flow conditions. Under batch conditions, 2-propanol was found to be the best H-donor molecule, with ethyl levulinate giving the highest yield in GVL. The reactions occurring under continuous gas-flow conditions were found to be much more efficient, also showing excellent yields in GVL when EtOH was used as the reducing agent. These experiments clearly show that the ability to release hydrogen from the alcoholic H-donor/solvent is the main factor driving CTH processes, while the tendency to attack the esteric group is the key step in the formation of transesterification products

Catalytic Transfer Hydrogenolysis of Lignin-Derived Aromatic Ethers Promoted by Bimetallic Pd/Ni Systems

Catalytic transfer hydrogenolysis (CTH) of diphenyl ether (DPE), 2-phenethyl phenyl ether (PPE), and benzyl phenyl ether (BPE)as model molecules of α-O-4 and β-O-4 as well as 4-O-5 lignin linkagespromoted by bimetallic Pd/Ni systems is reported. Pd/Ni (Pd loading of 3 wt %) catalysts were synthesized by using a simple and economic coprecipitation technique, and its detailed physicochemical characterization was performed by means of H₂-TPR, XRD, TEM, and XPS analysis. In the presence of palladium as cometal, an almost complete conversion of DPE was reached after 90 min at a temperature of 240 °C while BPE and PPE C–O bond breaking could be achieved at milder reaction conditions. Pd/Ni bimetallic systems can be magnetically recovered and efficiently used up to eight consecutive recycling tests in the transfer hydrogenolysis of DPE. The investigated substrates were also tested using analogous Ni monometallic systems. Palladium as cometal present in the catalysts was proven to increase the C–O bond cleavage rates and decrease aromatic ring hydrogenation selectivity. The catalytic tests on all possible reaction intermediates clearly show that the hydrogenolysis cleavage in etheric C–O bond breaking was the rate-determining step under CTH conditions, while hydrogenations only take place in a successive step. Moreover, it has been demonstrated that the hydrogenation of phenol formed from CTH depends on the type of aryl groups that form the aromatic ether structure