Low-temperature CO oxidation by Pd/CeO2 catalysts synthesized using the coprecipitation method

• Pd/CeO2 catalysts of low-temperature CO oxidation were synthesized by coprecipitation method.
• Two types of Pd components: PdO nanoparticles and PdxCe1−xO2−δ solid solution were observed.
• HRTEM revealed PdO nanoparticles inside the agglomerates of support nanoparticles.
• XPS showed the catalysts calcination produced Pd species with Eb(Pd3d5/2)∼336 and ∼338 eV.
• TPR-CO revealed a high reactive oxygen in the composition of PdOx(s)/Pd–O–Ce(s) species.
• PdOx(s)/Pd–O–Ce(s) and PdxCe1−xO2−δ species both are responsible for low-temperature activity.

Pd/CeO2 catalysts synthesized using the coprecipitation method under a wide range of palladium loading and calcination temperatures were investigated in this study. Structural (XRD, TEM), spectroscopic (XPS) and kinetic (TPR-CO) methods were used to investigate the morphological and structural forms of the catalysts and identify the states of palladium as the active component on the CeO2 surface and in its bulk. It was found that the synthesis and subsequent calcination at 450 °C resulted in the formation of two main types of the catalyst components: PdO nanoparticles and PdxCe1−xO2−δ solid solution. Application of HRTEM allowed to establish the formation of aggregates where ceria or PdxCe1−xO2−δ nanoparticles were located around PdO nanoparticles. A subsequent calcination process resulted in partial dissolution of PdO nanoparticles in ceria lattice and formation of the surface compounds of palladium and ceria, PdOx(s)/Pd–O–Ce(s), which contain high reactive oxygen according to the TPR-CO data. Based on the XPS and TPR-CO data the catalytic activity at low temperatures (<100 °C) was determined by a combination of both palladium surface structures PdOx(s)/Pd–O–Ce(s) and palladium ions Pd2+ in the PdxCe1−xO2−δ bulk phase.

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