Silver palladium bimetallic core-shell structure catalyst supported on TiO2 for toluene oxidation

Abstract We show that silver palladium bimetallic core-shell structure catalysts supported on TiO2 substrate (Ag@Pd/TiO2) are highly active with a low palladium loading for toluene purification in oxidation reaction. The Ag@Pd catalysts were synthesized by galvanic replacement of Pd coating on Ag nanoparticles. Transmission electron microscopy (TEM), high-resolution TEM, and scanning TEM with energy dispersive spectrometer confirmed that the catalysts have a core-shell configuration, and are spherical in shape with an average diameter size of about 9.0 nm. The UV–vis absorption spectroscopy and selected area electron diffraction further proved that the intimate contact and different electronegativity of Ag and Pd in core-shell structure result in electrons transferring from Ag core to Pd shell, which increases local electron density around Pd atom. In addition, X-ray photoelectron spectroscopy reveals that such an increase of electron density on Pd active site in Ag@Pd/TiO2 catalyst can substantially strengthen the chemisorption with reactant of O2, further promote the phase transformation from Pd0 metal to PdO oxidation state, and finally maintain the normal operation of Pd0-PdO synergic mechanism during toluene oxidation reaction. Hence, compared to monometallic Pd/TiO2 catalyst, the as-prepared bimetallic core-shell Ag@Pd/TiO2 catalyst exhibits greatly higher toluene oxidation activity as a whole although its palladium loading value is just one third of Pd/TiO2. The high catalytic oxidation activity with a low Pd loading makes the Ag@Pd/TiO2 a promising catalyst for use in VOCs purification.