Characterisation and activity of praseodymium oxide catalysts prepared in different gases from praseodymium oxalate hydrate. Microscopic, thermogravimetric and IR spectroscopic studies

Abstract

PrO_1.833 and Pr₂O₃ catalysts have been obtained as final decomposition products of Pr₂(C₂O₄)₃· 10H₂O in different gases (O₂, N₂ and H₂). The decomposition processes were characterized by thermogravimetric (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD) and IR spectroscopy of the solid-phase products. The results indicate that the compound dehydrates in three steps at 100, 150 and 380 °C and that the anhydrous oxalate decomposes at 445 °C to form two phases of Pr₂O₂(CO₃) depending upon the atmosphere used for the reaction. On further heating PrO_1.833 is formed at 550 °C in O₂ and at 650 °C in N₂. In contrast, Pr₂O₃ was formed at 650 °C in H₂. Surface area measurements and scanning electron microscopy (SEM) have shown that PrO_1.833 produced at 700 °C has a different surface area depending on the gas used: 43 and 64 m² g^–1 for O₂ and N₂, respectively. The surface area of Pr₂O₃ formed in H₂ is 59 m² g^–1. The texture of the catalyst has been found to depend upon the decomposition atmosphere.

IR spectroscopy has been used to analyse (qualitatively and quantitatively) the gas-phase reaction products between room temperature and 400 °C from the dehydrogenation and dehydration reactions of propan-2-ol over PrO_1.833 and Pr₂O₃ catalysts. The results revealed that Pr₂O₃ is a selective dehydration catalyst at 275 °C, decomposing propan-2-ol into propene (ca. 80%). However, PrO_1.833 is a dual function dehydration/dehydrogenation catalyst.