Structural Characteristics and Catalytic Activity of Nanocrystalline Ceria−Praseodymia Solid Solutions

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Abstract

Ceria−praseodymia (CP) nanocrystalline solid solutions were prepared by a coprecipitation method and calcined at various temperatures to understand the thermal effects on the physicochemical properties of the nano-oxides. The structural and redox properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM-HREM), BET surface area (SBET), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature programmed reduction (TPR) techniques. The catalytic efficiency toward oxygen storage capacity (OSC) and CO oxidation activity have been investigated. The XRD results confirmed the successful incorporation of praseodymium into the ceria lattice through the formation of nanoscale face-centered cubic solid solutions. The TEM-HREM observations supported the nanocrystalline nature of the solid solutions, as indicated by XRD results. XPS results revealed the presence of cerium and praseodymium in both 3+ and 4+ oxidation states, and surface enrichment of Pr. The UV−vis DRS results revealed an increase of Ce3+ species, indicating enhanced reducibility of the ceria upon Pr doping. Raman spectral analysis provided strong evidence for enhanced formation of oxygen vacancies inline with UV−vis DRS results. TPR measurements showed an enhanced bulk reduction at much lower temperatures, indicating increased oxygen mobility in the samples which enable the enhanced oxygen diffusion at lower temperatures. Ceria−praseodymia solid solutions were found to be thermally quite stable, and exhibit high oxygen storage capacity and CO oxidation activity even after calcination at high temperatures.

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