Pd supported on tetragonal zirconia: Electrosynthesis, characterization and catalytic activity toward CO oxidation and CH4 combustion

Abstract

Catalysts made of Pd supported on ZrO2 were prepared via a sacrificial anode electrosynthesis route. Tetragonal zirconia was added to an electrolytic cell assembled for the preparation of colloidal Pd nanoparticles. Several samples were prepared varying the electrolysis time and thus the Pd loading in the nanocomposite. XRD analysis showed the presence of the tetragonal ZrO2 mainly and some small reflections due to monoclinic ZrO2. BET surface areas were in the range 70–80 m2g−1. The morphology and surface chemical composition of the nano-materials were, respectively, assessed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. From TEM evidence, the Pd-ZrO2 powders revealed to be composed of spherical Pd nanoparticles (average core diameter: 6.9±1.8nm) evenly dispersed on the surface of ZrO2 nano-grains (average grain size: 150±70nm, average size of crystallites composing each grain: 40±10nm). XPS allowed to quantify the surface elemental composition of the nanomaterials and to study the different chemical states of the nano-dispersed palladium. Catalysts were tested for CH4 total combustion and for CO oxidation. The conversion increased with Pd content in the CH4 combustion experiments whereas decreased with Pd content in the CO oxidation experiments. The apparent activation energies were about 25 and 9kcalmol−1 for CH4 combustion and CO oxidation, respectively. Hypothesis was made that different reaction mechanisms and different active sites were probably involved in the two reactions.