Reduced alkaline earth metal (Ca, Sr) substituted LaCoO3 catalysts for succinic acid conversion

Abstract

The effect of partial substitution of La by Ca and Sr in the catalytic activity of lanthanum cobaltite (LaCoO₃) was studied. Two series of La_1−xCa_xCoO₃ and La_1−xSr_xCoO₃ (x = 0, 0.2, and 0.4) reduced perovskites were prepared, characterized and evaluated in the succinic acid conversion at 200 °C and 6 MPa. The characterization results showed a larger Ca substitution in the La_1−xCa_xCoO₃ series, whereas carbonates as segregated phases up to x = 0.2 of Sr were obtained in the La_1−xSr_xCoO₃ series. In the Sr substituted perovskites, the oxidation of Co³⁺ to Co⁴⁺ neutralizes the electronic instability, whereas in the Ca substituted perovskites the presence of Ca²⁺ generates oxygen vacancies. The succinic acid conversion forms mainly succinic anhydride and 2-hydroxy-tetrahydrofuran by dehydration and hydrogenation processes. The highest initial rate of the reduced LaCoO₃ was attributed to the smallest Co crystal size with no segregated phases, compared to substituted catalysts.