Role of Fe-C-Al Sites for Low-Temperature CO Oxidation (∼50 °c) over the Fe-Oxide Nanoparticles Supported by Al₂O₃

Fe-oxide/Al2O3 samples (0.5-, 1.0-, 2.0-, and 4.0-Fe) containing various amounts of Fe-oxide on the porous Al2O3 were prepared by tr-CVD and subsequent annealing. The catalytic activities toward CO oxidation under a dry air atmosphere were examined in the temperature range of 30-350 °C. The activities varied upon the deposition amounts of Fe-oxide below 200 °C. At 50 °C, the activity order was 0.5-Fe, 1.0-Fe, 2.0-Fe, and 4.0-Fe, whereas it shifted to 2.0-Fe, 1.0-Fe, 0.5-Fe, and 4.0-Fe at a higher temperature region (100-150 °C). CO-TPD and -TPR results indicated that Fe-oxide structures were different qualitatively as well as quantitatively with respect to the deposition amounts of Fe-oxides. The surface analysis results of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry revealed the formation of the interfacial Fe-C-Al species. The population of Fe-C-Al of each Fe-oxide nanoparticle decreased as the deposition amounts of Fe-oxide increased (0.5-Fe, 2.0-Fe, and 4.0-Fe) correlating to the activity order at ∼50 °C. It suggested that the Fe-C-Al species can facilitate the lower temperature CO oxidation (at ∼50 °C) on the surface of Fe-oxide nanoparticles by activating oxygen atoms. However, the surface of Fe-oxide nanoparticles can effectively catalyze CO oxidation at a higher temperature (>100 °C) without the aid of the Fe-C-Al species.