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