Introduction: New nanomaterials based on porous amorphous aerogels composed of Al2O3 nanofilaments with a diameter of 5 nm were obtained by oxidation of metallic aluminum. Al2O3 nanofilaments were covered by a TiO2 monolayer to prepare a TiO2/Al2O3 composite aerogel. It has been shown that the hydrogen treatment of inactive aerogel formed by alumina nanofilaments and its composite TiO2/Al2O3 at temperatures of 923-1173 K gave rise to a catalytic activity in the cracking of propane. It was found that the hydrogen treatment at high temperatures resulted in the self-organization of Al2O3 intertwined nanofilaments (5 nm in diameter) and TiO2/Al2O3 composite into the η-Al2O3 nanocrystalline hollow nanotubes with a diameter of 33 nm and 6 nm-thick walls followed by packing these nanotubes into bundles. This transformation was evidenced by electron microscopy, transmission electron microscopy, low-temperature adsorption of nitrogen vapors, X-ray fluorescence and X-ray diffraction.
Method: The high-temperature hydrogen activation of aerogels prepared from Al2O3 and Al2O3/TiO2 nanofilaments significantly added to their efficiency in the cracking of propane compared both to the commercial platinum catalyst supported by alumina and the thermal cracking, as well.
Result & Conclusion: The mesoporous crystalline structure of alumina nanotubes ensured a high selectivity (63% ethylene) and a catalytic activity (0.3 mmol/g×s) in the cracking of propane over the temperature range of 923-1123 K. In the case of TiO2/Al2O3 nanotubes, the reaction products changed from ethylene mainly to propylene with the selectivity of 68% and the catalytic activity of 0.1 mmol/g×s in the same temperature range.