Pd Supported on Carbon Nitride Boosts the Direct Hydrogen Peroxide Synthesis

Herein, the development of an improved Pd on carbon nitride catalyst for direct H 2 O 2 synthesis from the elements is reported. Microcalorimetric CO chemisorption is used to characterize the chemical speciation of the Pd-selective and -unselective sites. Selectivity trends among the samples suggest that a bare metal surface with a differential heat of CO chemisorption ranging between 140 and 120 kJ mol –1 is responsible for the total O 2 hydrogenation, while a maximum threshold value of differential heat of CO chemisorption of approximately 70 kJ mol –1 is necessary for the partial hydrogenation of O 2 to H 2 O 2 . Such a low differential heat of CO chemisorption indicates a low exposed metallic Pd surface subjected to electron withdrawal from the surrounding ligands: i.e., the N functional groups on the carbon support. With respect to N-containing carbon nanotubes, carbon nitrides provide the following: a higher concentration of N sites, a flexible network of π-conjugated polymeric subunits with sp 3 linking subunits, and a flakelike morphology with high exposure of reactive C edge terminations. This results in a more effective kinetic stabilization of the electronically modified Pd species.