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.

Graphical abstractDuring reduction of Pd-rich, PdCu/SiO2 catalyst at ⩾400 °C, i.e. at the temperature frequently used in catalyst activation, some part of palladium escapes from the alloy state interacting with silica to Pd silicide. This effect triggers a switch in the crystallographic structure of the PdCu phase: from fcc to bcc, characteristic for Pd∼0.5Cu∼0.5.Figure optionsDownload full-size imageDownload high-quality image (143 K)Download as PowerPoint slideHighlights► H2 treatment of PdCu/SiO2 at ⩾400 °C results in drastic changes in the metal phase. ► Palladium leaves the alloy state and interacts with SiO2, forming palladium silicide. ► Pd removal from a Pd-rich, Pd–Cu alloy induces the fcc → bcc phase transformation.