Formation of Isolated Single-Atom Pd1 Sites on the Surface of Pd–Ag/Al2O3 Bimetallic Catalysts

The structure of Pd–Ag/Al2O3 samples with different Ag/Pd ratios has been studied by a complex of physicochemical methods (H2-TPR, XRD, H2-TPD, TEM). Catalysts have been synthesized by supporting an active component on α-Al2O3 and γ-Al2O3. X-ray diffraction analysis has revealed the formation of a Pd–Ag substitutional solid solution with a face-centered cubic crystal lattice owing to alloying of the Pd and Ag components. An increase in the Ag content in the composition of bimetallic nanoparticles hinders the formation of palladium hydride (PdHx), which is completely suppressed at a ratio of Ag/Pd > 0.5. Infrared spectroscopy of adsorbed CO has revealed the formation of single-atom Pd1 sites on the surface of supported Pd–Ag bimetallic nanoparticles isolated from each other by silver atoms. Analysis of the structural stability of isolated Pd1 sites has shown that, under conditions of CO adsorption at 150°C, the stability of the sites can be provided by an increase in the Ag/Pd ratio to ≥2.