Gode Thrimurthulu

Structural characteristics and catalytic performance of alumina-supported nanosized ceria–lanthana solid solutions

Alumina-supported nanosized ceria–lanthana solid solutions (CeO2−La2O3/Al2O3 (CLA) = 80 : 20 : 100 mol% based on oxides) were synthesized by a modified deposition coprecipitation method from ultra-high dilute aqueous solutions. The synthesized materials were subjected to various calcination temperatures from 773 to 1073 K to understand the surface structure and the thermal stability. Structural and redox properties were deeply investigated by different characterization techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR), and Brunauer–Emmett–Teller (BET) surface area. The catalytic efficiency was evaluated for CO oxidation at normal atmospheric pressure. BET surface area measurements revealed that synthesized samples exhibit reasonably high specific surface area. As revealed by XRD measurements, samples maintain structural integrity up to 1073 K without any disproportionation of phases. XPS results suggested that there is no significant change in the Ce3+ amount during thermal treatments due to the absence of undesirable cerium aluminate formation. A significant number of oxygen vacancies were confirmed from Raman and UV-vis DRS measurements. The CLA 773 sample exhibited superior CO oxidation activity. The better activity of the catalyst was proved to be due to a high dispersion in the form of nanosized ceria–lanthana solid solutions over the alumina support, facile reduction, and a high oxygen storage capacity.

Nanocrystalline ceria–praseodymia and ceria–zirconia solid solutions for soot oxidation

The relative effects of Zr4+ and Pr3+/4+ dopants on the structure, redox properties, and catalytic performance of nanosized ceria was studied. The investigated ceria–zirconia and ceria–praseodymia (CP) solid solutions were prepared by a modified coprecipitation method, characterized by a variety of techniques, and evaluated for soot oxidation. The characterization results indicate that CP has more surface and bulk oxygen vacancies, redox sites, and lattice oxygen mobility, and better thermal stability. Besides having low specific surface area, CP is more active in soot oxidation. This better activity has been attributed to the presence of more surface and bulk oxygen vacancies, which promote the adsorption of gas-phase oxygen and the formation and mobility of large numbers of active oxygen species.

Nanocrystalline alumina-supported ceria–praseodymia solid solutions: structural characteristics and catalytic CO oxidation

In this work, alumina supported ceria–praseodymia (CP/A) samples were synthesized by a deposition coprecipitation method. The structural, textural, and redox properties of the prepared samples were characterized at different calcination temperatures from 773 to 1073 K and their catalytic activity was assessed in the CO oxidation reaction. In order to determine the promoting effect of the alumina support in the sample, the physicochemical and catalytic properties of CP/A were compared with unsupported ceria–praseodymia (CP) solid solutions. The X-ray diffraction results indicated the formation of ceria–praseodymia solid solutions over the alumina support. The nanocrystalline nature of the samples was confirmed by transmission electron microscopy. The CP/A sample showed an extremely high surface area which remained reasonably high even after calcination at 1073 K. The combined analyses revealed that the CP/A sample had more oxygen vacancies than CP. The H2-temperature programmed reduction results suggested that the active oxygens were significantly improved in CP/A over CP. The characterization results also highlighted the excellent thermal stability of CP/A. The CO oxidation profiles signified that the catalytic activity of CP/A calcined at 773 K was remarkably enhanced in comparison to that of CP. The fine dispersion of ceria–praseodymia solid solutions over the alumina support in the process of deposition coprecipitation and the synergistic effect between ceria–praseodymia and the support, which resulted in very high surface areas, oxygen vacancy concentrations, and active oxygen species, are believed to be responsible for the superior activity of the CP/A sample.