Effect of treatment at high temperatures on morphology of a carbon supported Pd catalyst investigated by X-ray diffraction and photoelectron spectroscopy aided with QUASES

Abstract

The 20 wt% Pd supported on carbon Vulcan XC-72 (Pd/C) anode catalyst, used to formic acid (FA) electro-oxidation reaction, submitted to different high temperature treatment (HTT) procedures in the temperature range 200–400 °C was studied using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) aided with Quantitative Analysis of Surfaces by Electron Spectroscopy (QUASES).The HTT procedures increased the diameter of Pd crystallites influencing their electronic properties, led to formation of surface PdO and PdO2 from the respective bulk Pd oxides, decreased Pd oxide content and PdOx overlayer thickness. Carbon incorporation into Pd with PdCx composition of x < 0.01 (200 °C), x ∼ 0.015 (300 °C) and x ∼ 0.04 (400 °C) was observed (XRD). The XRD confirmed that FA reduces the surface PdOx to Pd increasing Pd metallic nanoparticle diameter. The values of Pd nanoparticle diameter and PdOx overlayer thickness obtained from QUASES and corrected for elastic electron scattering effects are in better agreement with the values resulting from XRD and Stohmeier equation, respectively. Due to this correction the root-mean-square (RMS) deviations between Pd nanoparticle diameter determined by QUASES and XRD decrease from 21.5% to 19.8%, whereas deviations between the PdOx overlayer thickness evaluated by QUASES and Stohmeier equation decrease from 54.8% to 22.8%.