Nb-doped hematites for decomposition of isopropanol: Evidence of surface reactivity by in situ CO adsorption

Abstract

A series of Nb-containing hematites, Fe 2− x Nb x O 3 (%Nb = 0.00, 1.49, 5.00 and 9.24) were prepared using a conventional co-precipitation method. Room-temperature Mössbauer spectroscopy and powder X-ray diffraction measurements suggested the formation of a crystalline phase with partial substitution of Fe 3+ by Nb 5+. The reactivity of these Fe 2− x Nb x O 3 materials as catalysts was investigated using the decomposition of isopropanol as a model reaction. Theoretical calculations and CO adsorption monitored by in situ infrared absorption spectroscopy showed that the presence and the position of substituting niobium atoms in the structure of hematite modify its surface properties. The results from this study also show that the presence of Nb changes the catalytic properties toward a preferential formation of propene, presumably because of the addition of oxygen vacancies. All catalysts show high catalytic activity, and reach total isopropanol conversion above 375 °C. Moreover, the material with high Nb content reaches total conversion at lower temperatures, at approximately 290 °C with conversion to propene of 92%.