Effect of La2O3-dopping on the Al2O3 supported cobalt catalyst for Fischer-Tropsch synthesis

Alumina was doped with lanthana, La2O3, by either impregnation or co-precipitation. The doped and undoped alumina was then used as supports for the preparation of cobalt catalysts by incipient wetness impregnation. The catalysts prepared were characterized by nitrogen adsorption–desorption, powder X-ray diffraction, hydrogen temperature programmed reduction, hydrogen temperature programmed desorption, O2-titration and diffuse reflectance infrared Fourier transform spectroscopy, and the catalytic properties for Fischer-Tropsch synthesis (FTS) have been evaluated. The results showed that La2O3-dopping impacted the catalytic performance significantly. The catalyst with the La2O3-doped support prepared by co-precipitation showed better reducibility, activity and product selectivities. The higher ratio of the octahedral to tetrahedral cobalt species of the co-precipitated catalyst relative to the catalyst doped by impregnation might have caused the enhanced performance. The presence of the hydrocarbonyl species, distinguished by its vibrational feature, is directly related to CO conversion and chain-growth.

The DRIFTS spectra of syngas adsorbed on reduced catalysts were collected at 503 K. The new peak located at 2058 cm−1 is not only directly related to the bands of hydrocarbon (2800–3100 cm−1), but also related to CO conversion and chain-growth. This peak is ascribed to the “hydrocarbonyl” species, may be a vibrational feature of some reaction intermediate.Figure optionsDownload high-quality image (116 K)Download as PowerPoint slide