Sustainable direct H2O2 synthesis over Pd catalyst supported on mesoporous carbon: The effect of surface nitrogen functionality

We employed oxygen- and nitrogen-functionalized mesoporous carbons (OMC and N-OMC) as supports for Pd nanoparticles pre-formed via a modified colloidal method. In the direct synthesis of hydrogen peroxide (H2O2) from H2 and O2, the prepared Pd/OMC catalyst outperformed a commercial Pd catalyst supported on activated carbon (Pd/AC) and a Pd catalyst on oxygen-functionalized carbon nanotubes (Pd/OCNT) in terms of H2O2 productivity, emphasizing the advantage of mesoporous carbon support. An even higher H2O2 productivity was obtained over Pd catalyst supported on N-OMC with 2.72 at.% nitrogen on the surface. However, a further increase of surface nitrogen content to 13.26 at.%, as the case of mesoporous carbon directly grown using N-containing carbon precursor (NMC), led to increased activity (in terms of H2 consumption) but poor H2O2 productivity. X-ray photoelectron spectroscopy analyses of the Pd/MC catalysts suggest that a suitable amount of N groups (ca. 2.72 at.%) on the MC surface led to a high fraction of Pd2+ in the Pd/MC catalyst, which is believed to be important for achieving high selectivity in direct H2O2 synthesis. These results highlight that tuning the surface properties of carbon supports is a versatile approach to fabricate highly selective supported Pd catalysts for the sustainable direct synthesis of H2O2 from H2 and O2.