Effects of melting temperature on cerium oxidation state and crystallization on catalytic properties in cerium phosphate glasses

Abstract

The effect of the melting temperature on the cerium oxidation state and crystallization of cerium phosphate glasses with a molar composition 30CeO 2 70P 2 O 5 was investigated. Ce 3+ and Ce 4+ ion concentration changes in the glass attributable to the melting temperature were investigated by X-ray photoelectron spectroscopy analysis. The crystallization kinetics of the glasses and the activation energy for crystallization were evaluated under non-isothermal conditions using differential thermal analysis (DTA) performed at different heating rates. Each DTA curve exhibited one exothermic peak associated with the crystallization of the glass. The crystalline phase was identified as CePO 4 via X-ray diffractometry analysis. The Kissinger and Marotta methods were used to calculate the local activation energies for the glass samples. The amount of precipitated CePO 4 with heating at 890 K increased as the melting temperature (or Ce 3+ ) increased. The catalytic properties were studied by thermogravimetric analysis, which showed that a greater amount of precipitated CePO 4 led to poorer catalytic properties of the glass.

Crystallization of Rare-Earth Phosphate-Borosilicate Glass Composites Synthesized by a One-Step Coprecipitation Method

“…This trend suggests that lower annealing temperatures favored the formation of CeO 2 over CePO 4 , which has been observed previously . This can once again be explained by the temperature-dependent Ce redox couple (4Ce 4+ + 2O 2– ⇌ 4Ce 3+ + O 2 ), which favors Ce 4+ at lower temperatures. , The relative amount of Ce 4+ compared to Ce 3+ is inversely proportional to temperature in the exothermic reduction reaction . CeO 2 would be favored to form at lower annealing temperatures, as CeO 2 contains Ce 4+ , while CePO 4 contains Ce 3+ .…”

“…Formation of CeO 2 was favored over CePO 4 at lower annealing temperatures due to the Ce redox couple, which favors Ce 4+ at lower annealing temperatures. , More CePO 4 and less CeO 2 was observed to be present when the CePO 4 –BG composite materials were made using a Ce 3+ precursor compared to when a Ce 4+ precursor was used (Table ). It has been shown previously that the activation energy for the formation of CePO 4 decreases as the amount of Ce 3+ increases . A maximum amount of Ce 3+ is present by starting with a Ce 3+ precursor.…”

“…39,40 The relative amount of Ce 4+ compared to Ce 3+ is inversely proportional to temperature in the exothermic reduction reaction. 42 CeO 2 would be favored to form at lower annealing temperatures, as CeO 2 contains Ce 4+ , while CePO 4 contains Ce 3+ . Any Ce that was not present in crystalline phases was not able to be detected by the analysis of powder XRD patterns.…”

“…It has been shown previously that the activation energy for the formation of CePO 4 decreases as the amount of Ce 3+ increases. 42 A maximum amount of Ce 3+ is present by starting with a Ce 3+ precursor. This leads to the amount of CePO 4 being maximized and the amount of CeO 2 being minimized when a Ce 3+ precursor is used compared to when a Ce 4+ precursor is used.…”

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions

“…The first stage, around 573–623 K, is mainly attributed to Ce 3+ oxidation according to the available literature. 92 , 93 The second degradation period, above 773 K, is present mainly for BCW since only it has a large amount of W 4+ ions prone to fast oxidation toward W 5+/6+ which are the main ingredients of CCWO at that point. 94 − 96 Unstable WO 3– x species containing 5+ ions have a higher heat-tolerance factor but will also start oxidizing since their decomposition barrier does not fall much above that threshold, though at a much slower pace.…”