Abstract
Acid−base properties of alumina-supported rare-earth oxides (Ln/Al2O3; Ln = La, Ce, Eu, Tb, and Yb) were investigated with α-pinene isomerization, 2-butanol decomposition, and temperature-programmed desorption and FTIR techniques. The structural characterization was carried out by means of XRD, Raman, and XAFS spectroscopies. Differences in the catalyses, acid−base properties, and structures of Ln/Al2O3 catalysts because of loaded elements and the amounts were discussed. The addition of a lanthanoid atom (Ln) to γ-Al2O3 poisons both the original base and acid sites of γ-Al2O3 and generates new-type Lewis acid site. In a series of Ln/Al2O3 catalysts, 0.2−0.5 mmol of Yb/Al2O3 exhibited the highest activity for α-pinene isomerization. The supported Yb species form Yb−O−Al linkage which acts as a Lewis acid. The local structure around Yb and a generation mechanism of acidic property are analogous with Yb/Al2O3 and Yb/SiO2.
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