Enhancing the selectivity of Pd/C catalysts for the direct synthesis of H2O2 by HNO3 pretreatment

Abstract

Pd/C catalysts are one of the most efficient catalysts for direct synthesis of H₂O₂ from H₂ and O₂ (DSH), while pretreating the activated carbon by HNO₃ will influence the performance of the Pd/C catalyst. In this paper, a series of HNO₃-pretreated and N₂-calcinated activated carbon-supported Pd catalysts were prepared and evaluated for the DSH reaction at ambient temperature. The experimental results showed that using HNO₃-pretreated activated carbon as the support enhanced H₂O₂ selectivity greatly, and the highest H₂O₂ selectivity of 90% was obtained on 20 wt% HNO₃-pretreated catalyst. The catalysts were systematically characterized by multiple techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, Boehm titration and other techniques. It was found that the textural properties of activated carbon did not affect the catalytic performance, while the effects of acid functional groups of activated carbon were supposed to improve the H₂O₂ selectivity, and lower H₂O₂ decomposition and hydrogenation capacities of the catalyst.