Effect of the preparation method on the properties of zirconia-ceria materials

Abstract

Zirconium-cerium mixed oxides were prepared by two methods: (i) sol-gel hydrolysis of alcoholic solutions of zirconium alkoxides (n-propoxide and n-butoxide) in the presence of aqueous solutions of cerium nitrate (method SG) or (ii) coprecipitation of aqueous solutions of zirconyl and cerium nitrates by ammonia (method NP). Dried or calcined solids were characterized by XRD, DTA, BET and oxygen storage capacity (OSC ) measurements, O 2 adsorption was monitored by infrared spectroscopy. Regardless of the zirconium precursor, SG samples calcined at 900 °C have a fluorite-type structure with BET surface areas varying between 35 and 45 m2 g−1. Cerium-rich samples (0.85∏x∏0.90), with excellent OSC properties and high thermal stability can be prepared by the sol-gel method. FTIR studies of O 2 adsorption reveal the presence of stable superoxide species whose concentration strongly depends on the cerium content and the method of preparation. A good correlation between the relative amount of O 2 − species and OSC values was observed. Superoxide ions may be formed at the same anionic vacancies as those involved in oxygen storage.Sol-gel method. Two Zr precursors were used: zirconium n-

Ceria‐Based Solid Catalysts for Organic Chemistry

“…[4] Since the pioneering works of Yao and Yu Yao [2] and of Su et al, [5,6] many studies have been devoted to improving knowledge of the kinetics of OSC [7][8][9] and of the mechanisms implicated in surface and bulk oxygen mobility in ceria and related compounds, [10][11][12][13][14] with a special insight into CeZrO x oxides. [15][16][17][18][19] Oxygen diffusivity in these materials can be measured by 18 O/ 16 O isotopic exchange, [20][21][22] while oxygen species (e.g., superoxides, peroxides) that might be involved in the diffusion process can be investigated by electron spin resonance (ESR) [23][24][25][26][27] or FTIR. [18,[28][29][30][31] ESR studies have shown that the presence of a metal (Pt, Rh) drastically changes the nature of the oxygen species; the metal favoring the formation of O À ions instead of superoxide species.…”

“…[15][16][17][18][19] Oxygen diffusivity in these materials can be measured by 18 O/ 16 O isotopic exchange, [20][21][22] while oxygen species (e.g., superoxides, peroxides) that might be involved in the diffusion process can be investigated by electron spin resonance (ESR) [23][24][25][26][27] or FTIR. [18,[28][29][30][31] ESR studies have shown that the presence of a metal (Pt, Rh) drastically changes the nature of the oxygen species; the metal favoring the formation of O À ions instead of superoxide species. [26] The presence of certain impurities in ceria, such as chloride ions, can also affect the nature and amounts of surface oxygen species.…”

Synthesis of CeO2–ZrO2 solid solution by glycothermal method and its oxygen release capacity

“…It has been reported that the oxygen storage capacity (OSC) is generated by interconversion between Ce 4+ and Ce 3+ under oxidative and reductive conditions [5,6]. The OSC of the CeO 2 -ZrO 2 solid solution depends largely on the method of preparation; many physical properties such as crystallinity, crystallite and particle sizes, and homogeneity change depending upon its preparation methods and, thus, influence the OSC [7], and many methods such as solid-state reaction [8], high-energy milling [9], coprecipitation method [10,11], sol-gel method [12,13], citrate complex method [14], polymerized complex method [15], combustion synthesis [16,17], and hydrothermal method [18,19] have been reported.…”

Modeling 1D structures on semiconductor surfaces: synergy of theory and experiment

“…163,164 Kockmann et al 155 and later Niikura et al 101 , however, showed this not to be the case for Au-induced NWs on Ge(001). Kockmann et al 155 showed that, since STM images are a convolution of the surface and the STM tip's electronic structure, the shape of the latter will lead to a variety of STM images (cf.…”