Pd-Te Alloy Catalysts For Hydrogen Peroxide Synthesis Directly From Hydrogen And Oxygen

As a green oxidant, hydrogen peroxide (H2O2) is widely used in various fields. Presently, the most commonly manufactured method is an anthraquinone procees (AQ). However, it suffers from several drawbacks including high investment, heavy pollution and security problems. Compared with the AQ process, direct synthesis of H2O2 from H2 and O2 is environmental friendly and simple with atom economy. While, it has not been applied practically, due to the low efficiency of catalysts and the safety concerns.In the study, a series of Pd-M (M= Sn, Cu, Te) catalysts were prepared by incipient wetness impregnation, among which the Pd-Te/Al2O3 catalysts exhibited a higher H2O2 yield and selectivity. The electronic and geometric structures of catalysts were studied systematically by using inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-rays photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), temperature programmed stripping (TPD). Results show that Pd particles disperse uniformly on the support. With the variation of Te loading, the size (ca.1.7-2.0 nm in diameter) and crystallinity of Pd particles have shown no discernible differences. Te and Pd form Pd-Te alloy, and the strong mutual interaction between Pd and Te modifies the geometric and electronic structures of Pd, which consequently leads to the changes of the activity of catalysts. The addition of Te suppresses the adsorption of H2 and weakens the dissociative activation of O2, which can effectively restrain the decomposition of H2O2 and the formation of H2O, increasing the H2O2 selectivity. In addition, Te can inhibit the leaching of Pd, thus increasing the stability of the catalyst. On the basis of these results, the effect of active support TiO2 on the Pd-Te alloy catalysts were investigated. The results show that reductive thermal treatment can improve the H2O2 selectivity, among which the Pdioo.oTei.o/Ti02 catalyst shows the highest selectivity of H2O2 (> 98%). CO-DRIFTS results show that the configuration of Pd can be changed by the thermal treatment. A small amount of Pdσ+ species as well as a large number of monodisperse Pd active sites were observed in the Pdioo.oTei.o/Ti02 catalyst. The former can inhibit the decomposition of H2O2, and the latter is conducive to the non-dissociative activation of O2, thus improving the H2O2 selectivity.