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Abstract

The behavior of Pd nanoparticles deposited by sol-immobilization on N-doped nanocarbon (carbon nanotube-like from Pyrograf Products; N-CNT-like) is studied in the direct synthesis of H2O2 and compared with those of the undoped catalysts or prepared by the same Pd deposition method on active carbon (Vulcan XC-72) as the support. The catalytic tests were carried out using a slurry batch- or semi-continuous reactor at room temperature and a total pressure of 10 bar using CO2-expanded methanol as the solvent. The Pd on N-CNT-like gives high productivities to H2O2, comparable to the best literature results, while the selectivity to H2O2 is low due to the low oxygen partial pressure and likely low oxygen coverage on Pd particles. The introducing of nitrogen in the CNT-like material favors not only the dispersion of Pd (with a consequent improvement of the activity), but also the specific turnover, due to probably the electronic effect of pyridine-like nitrogen sites present in the N-CNT-like support favoring the O2 surface coverage. However, the introduction of these N functionalities on the surface has also a negative effect on the rate of H2O2 consecutive conversion to water.