Abstract
The selective hydrogenation of resorcinol (RES) to 1, 3-cyclohexanedione (1,3-CHD) without the addition of alkali is a big challenge. In this article, a novel reduced graphene oxide (rGO) supported Pd catalyst was prepared through co-reduction method, over which we obtained 99.9% of resorcinol conversion and 94.2% of the ever-reported highest 1,3-cyclohexanedione selectivity at 25 °C in only CH2Cl2 solvent. The excellent selectivity was contributed to the strong π-π and p-π interactions between the graphene nanosheet and the benzene ring as well as hydroxyl in RES molecule. The followed adsorption experiment and Raman analysis also showed the existence of aromatic graphite structures in rGO, which exhibited stronger adsorption towards RES than towards 1,3-CHD.
Highlights
Benzene ring in phenol by hydrogenation[13], the benzene ring in RES is more reactive as it is activated by one more adjacent hydroxyl groups through electron-donating effect, which would make the energy barrier of the addition of the first H2 molecule be much closer to that of the addition of the remaining two H2 molecules
It can be seen that Pd/rGO catalyst exhibited much higher selectivity to 1, 3-CHD than the other Pd catalysts used in this work: in the experimental ranges, most of the selectivity to 1,3-CHD was more than 80% with a high conversion of RES over Pd/rGO catalyst
1,3-CHD selectivity was as high as 93.2% over Pd/rGO at 25 °C, but dropped to 83.5% at 40 °C. 1,3-CHD selectivity decreased from 86.2% to 54.5% at 40 °C as the hydrogenation pressure varied from 0.1 MPa to 2 MPa
Summary
Benzene ring in phenol by hydrogenation[13], the benzene ring in RES is more reactive as it is activated by one more adjacent hydroxyl groups through electron-donating effect, which would make the energy barrier of the addition of the first H2 molecule be much closer to that of the addition of the remaining two H2 molecules. Wang et al.[14] reported that C3N4-supported Pd catalyst showed better adsorption of phenols, over which 99% of selectivity toward cyclohexanone were obtained during phenol hydrogenation.
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