Three-dimensionally ordered macroporous CeO2/Al2O3-supported Au nanoparticle catalysts: Effects of CeO2 nanolayers on catalytic activity in soot oxidation

Abstract

A series of catalysts consisting of three-dimensionally ordered macroporous (3DOM) x-CeO2/Al2O3-supported Au nanoparticles (x = 2, 10, 20, and 40 wt%) were successfully synthesized using a reduction-deposition method. These catalysts were characterized using scanning electron microscopy, the Brunauer-Emmett-Teller method, X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, and temperature-programmed reduction by H2. Au nanoparticles of mean particle size 5 nm were well dispersed and supported on the inner walls of uniform macropores. The 3DOM structure improved the contact efficiency between soot and the catalyst. An Al-Ce-O solid solution was formed in the multilayer support, i.e., x-CeO2/Al2O3, by the incorporation of Al3+ ions into the CeO2 lattice, which resulted in the creation of extrinsic oxygen vacancies. Strong interactions between the metal (Au) and the support (Ce) increased the amount of active oxygen species, and this promoted soot oxidation. The catalytic performance in soot combustion was evaluated using a temperature-programmed oxidation technique. The presence of CeO2 nanolayers in the 3DOM Au/x-CeO2/Al2O3 catalysts clearly improved the catalytic activities in soot oxidation. Among the prepared catalysts, 3DOM Au/20%CeO2/Al2O3 showed high catalytic activity and stability in diesel soot oxidation.