TPO characterization of ethanol reduced Pd nanoparticles supported on SiO2

Silica-supported Pd catalysts were prepared at 298–353 K from Pd(II) chloride or Pd(II) acetate in suspension of SiO2 and ethanol-water or ethanol-toluene mixtures, respectively. Reduction of Pd ions diffusing from liquid phase was ensured in an ethanol-rich adsorption layer covering the SiO2 particles. Temperature-programmed oxidation (TPO) measurements were performed to characterize the organic impurities retained by solid phase. Vapour phase reduction/adsorption experiments with ethanol confirmed that under the reported reduction conditions, the Pd nanoparticles decompose ethanol and the CO formed remains chemisorbed on the Pd sites. Upon contacting the samples with air during the drying process to eliminate the solvent, the CO molecules are immediately removed from Pd sites by O2, and thereby, a significant fraction (22–34%) of Pd sites becomes accessible for catalytic reactions.