Abstract:

Carbon/alumina (titania) composites have unique physicochemical properties and have been widely used in adsorption and catalysis. Carbon in these composites greatly influences the sintering and phase transformation behavior of the oxides. Calcining carbon/γ-Al2O3 in oxygen at high temperature results in a quick γ-to α-Al2O3 transformation. In nitrogen, X-ray diffraction (XRD) analysis showed that carbon inhibited the phase transformation significantly. This inhibition effect was found to be carbon content dependent. For the carbon/titania system, pure titania and carbon-protected-titania samples were calcined at different temperatures and analyzed by XRD, transmission electron microscopy (TEM), and Raman spectroscopy. Surface area and pore size analysis was performed by isothermal nitrogen adsorption-desorption. Results show that the carbon layer can improve the thermal stability of the TiO2 nanoparticles and hinder the phase transformation of anatase to rutile at up to 800 ℃ under nitrogen-protected heat treatment. On the other hand, carbon can be removed by controlling calcination in oxygen at 500 ℃ without affecting the phase composition and texture of titania. The carbon removal efficiency was examined by temperature-programmed oxidation (TPO) analysis. Therefore, carbon can be used as a special surface modifier which can inhibit the high temperature phase transformation of oxides without introducing alien elements effectively.

Key words: Carbon, Alumina, Titania, Phase transformation, Anatase, Rutile