Phase transformations in silica-supported Pd–Cu catalysts during reduction in hydrogen

This work provides evidence that reduction of Pd–Cu/SiO2 catalysts in dihydrogen at temperatures as low as 400–450 °C may lead to drastic changes in the metal phase. A significant part of palladium leaves the alloy state and enters into interactions with silica, forming a palladium silicide. In effect, a considerable shortage of palladium in originally prepared Pd0.75Cu0.25/SiO2 catalyst leads to a change in the crystallographic structure of the Pd–Cu phase: from fcc to bcc, characteristic for Pd∼0.5Cu∼0.5. This result seems significant in view of a common usage of this temperature in activation of silica-supported bimetallic Pd-based catalysts.