An Temperature-Dependent Study of LaO Reactivation Process.

Lanthanum-containing materials are widely used in oxidative catalytic and electrocatalytic reactions such as oxidative coupling of methane (OCM) and solid oxide fuel cells (SOFCs). However, many of these materials are highly susceptible to air contamination which means characterization results generally cannot be associated with their reactivity. In this study, the activation processes of an -prepared bulk LaOCO sample and an as-prepared La(OH) sample are investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and online mass spectroscopy (MS). Results indicate that the LaOCO sample, during linear heating to 800°C, always contains some carbonates near the surface region, which supports a two-step model of bulk carbonate decomposition through surface sites. The La(OH) sample structure evolution is more complex due to contaminations from air exposure. Together with TGA results, online mass analysis of water and CO signal loss showed that three major catalyst structure phase change steps and a preheating up to 800°C are required for the as-prepared material to be transferred to LaO. This process is carefully investigated combining the three methodologies. XPS and XRD data further reveal transformations of variety of surface structures and forms including hybrid phases with hydroxyl, carbonates, and oxide as the sample heated to different temperatures within the range from 200 to 800°C. The results provide useful insights on the activation and deactivation of La-contained materials.