Direct synthesis of hydrogen peroxide over palladium catalysts supported on glucose-derived amorphous carbons

摘要

Untreated and sulfonated biomass-derived amorphous carbons were prepared by the pyrolysis of D-glucose at different temperatures, followed by sulfonation. Not only the surface functional group concentration but also the structure of polyaromatic carbon sheets was significantly affected by the carbonization temperature and sulfonation. More importantly, the carbonization temperature played a crucial role in determining the size of Pd nanoparticles (NPs) on glucose-derived carbons (GCx) and thereby affected the catalytic performance of Pd/GCx for the direct synthesis of hydrogen peroxide (DSHP). The volcano-shaped dependency between the Pd NP size and the carbonization temperature of GCx agrees well with the reverse relationship between the Pd NP size and the catalytic activity of Pd/GCx. The flexible polyaromatic carbon sheet structure of the GCx was beneficial in increasing the sulfonic acid group content on the carbon surface and, therefore, H2O2 selectivity was improved in the presence of the Pd/S-GC2 catalyst (Pd supported on the sulfonated glucose-derived carbon pyrolyzed at 723 K). However, both H-2 conversion and H2O2 productivity decreased over the same catalyst, possibly due to the decreased number of active sites on the clustered or single-site Pd. Reducing the catalyst resulted in a decrease in H2O2 selectivity by significantly lowering the Pd2+/Pd-0 ratio and increasing the Pd NP size. These results clearly demonstrate that fine control of the physicochemical properties of the active metal and GCx support and their synergistic combination is essential to realize an efficient Pd catalyst supported on GCx for the DSHP reaction.