Highly active PdCeOx composite catalysts for low-temperature CO oxidation, prepared by plasma-arc synthesis

Abstract

The plasma-arc method was adapted for the synthesis of composite palladium–ceria catalysts, which were utilized for the low-temperature oxidation of carbon monoxide. The Pd/CeO2 catalysts were synthesized in two steps: step 1 – direct synthesis of palladium–cerium–carbon composite PdCeC in the plasma-arc chamber, and step 2 – calcination of the composite with carbon burnout in air at 600, 700, and 800°C. Catalytic testing using temperature-programmed reaction demonstrated the high efficiency of the synthesized catalysts during the oxidation of carbon monoxide and their ability to oxidize CO at temperatures as low as room temperature. In comparison with a catalyst that had similar morphology and palladium content but was prepared by coprecipitation, the synthesized catalyst showed that the calculated TOF value for the composite catalyst was two–three times higher than that of the catalyst prepared by chemical methods.A variety of physical methods (HRTEM, XRD, XPS, Raman spectroscopy and others) were used to examine the microstructure, composition and electronic state of the composite components in detail after the high-temperature calcination stage of catalyst synthesis. It was shown that high catalytic activity was provided by the formation of a high-defect fluorite structure of PdCeOx solid solution and highly dispersed PdOx nanoparticles. The XPS data suggest that carbon nanostructures mixed with palladium and cerium in the initial PdCeC composite prevent sintering during high-temperature calcination and play a key role in the formation of a high-defect solid solution of palladium in the CeO2 structure, which has a high concentration of Ce3+ and oxygen vacancies.