Effect of Pr on the electrical and chemical properties of cerium oxide prepared by combustion method

Abstract

Nanoparticles of Ce 1−x Pr x O 2 (X: 0.6 and 0.8), were synthesized by the combustion method using citric acid as chelating and fuel agent. The X-ray diffraction patterns and Rietveld refinements confirm that samples shown as a single phase in a cubic fluorite structure, with an increase in the lattice parameter as a function of Pr concentration. The crystallite size domains obtained by the Scherrer formula, confirm values around 10 and 37 nm. The scanning electron microscopy images, show that the solids are composed of dense heterogeneous aggregates. The X-ray photoelectron spectroscopy, reveals that oxides are composed of cerium and praseodymium cations in oxidation states 4+ and 3+ respectively. The TPR-H 2 profiles indicate that cerium and praseodymium cations present in the obtained systems are completely reduced to Ce 3+ and Pr 3+ at temperatures above 790°C. The impedance spectroscopy data at room temperature showed that the conduction processes for the two systems take place at the grain boundaries. The Ce 0.2 Pr 0.8 O 2 system offer lower resistance, due to the high amount of Pr 3+ ions inserted in the structure and the high amount of oxygen vacancies formed in the synthesis process.

The dependence of high catalytic performance on the tunable oxygen vacancy in the CZxS/Zn‐HZSM‐5 bifunctional catalyst for alkylation of benzene and syngas

“…[ 36,37 ] On the basis of Table 1, it is evident that there were more oxygen vacancies on the surface of CZ x S samples, and reached a maximum for a Zr/Ce ratio of 4. [ 26,38,39 ]…”

“…[36,37] On the basis of Table 1, it is evident that there were more oxygen vacancies on the surface of CZ x S samples, and reached a maximum for a Zr/Ce ratio of 4. [26,38,39] The H 2 -TPR was used to evaluate the reducibility of CZ x S samples and the results were showed in Figure 5. All samples exhibited two broad reduction peaks (α & β), and the reduction peak (α) at low-temperature within the F I G U R E 4 XPS spectra of Ce3d (a) and O1s (b) for CeO 2 , CZ 2 S, CZ 4 S, and CZ 6 S samples range of 358-445 C has been ascribed to the reduction of the surface adsorbed oxygen species, and the reduction peaks (β) at a high-temperature within the range of 480-610 C was related to the reduction of bulk oxygen species that required a large amount of energy.…”