Analytical characterisation of Pd/ZrO2 composite nanoparticles employed in heterogeneous catalysis

Pd/ZrO2 nanocomposite materials were synthesised following a two-step procedure. Firstly, tetragonal zirconia was prepared via a chemical route; then it was subjected to an in-situ electrochemical impregnation with palladium nanoparticles. Different process times lead to a different Pd loading in the resulting material. Pd/ZrO2 powders were subjected to morphological and spectroscopic characterisation. Transmission electron microscopy (TEM) analysis showed that ZrO2 nanograins have an average size of 150 +/- 70nm, and are composed of smaller sub-grains (average diameter = 40 +/- 10 nm). Spherical Pd nanoparticles are evenly dispersed on the oxide support, their average core diameter being 6.9 +/- 1.8 nm. X-ray Photoelectron Spectroscopy (XPS) was used to asses the materials surface chemical composition. Testing the catalysts for the CO oxidation revealed an appreciable activity of the Pd-modified ZrO2 samples. TEM and XPS analyses were also performed on materials exposed to prolonged catalytic runs and contributed to shed light on the catalysis mechanism. A rationale for the results obtained on the CO conversion process was proposed, invoking a key- catalytic role of finely dispersed PdO sites. The nanomaterial morphological stability and reactivity encouraged to employ it in the Heck synthesis of butyl cinnamate. This process was demonstrated to take place with high conversion values and interesting stability towards catalyst recycling.