Structural analysis of La/Al₂O₃ catalysts by La K-edge XAFS

Structural analysis of La/Al₂O₃ catalyst materials was carried out by means of XRD and La K-edge XAFS. Influences of loading amounts and treatment temperature on the local structure around La were investigated. La atoms are supported on γ-Al₂O₃ in a highly dispersed form when a loading amount is less than 0.2 mmol g(Al₂O₃)-1, and structural transformation of the La species does not take place in the temperature ranges of 873-1273 K. La species of highly loaded catalysts start to change their structure from oxide-like form to the aluminate at 1073 K. Formation of LaAlO₃ perovskite on the catalyst surface requires a concentration of La atoms above 0.5 mmol g(Al₂O₃)⁻¹ (7.5 wt% as La₂O₃).