Nanosized Au supported on three-dimensionally ordered mesoporous β-MnO2: Highly active catalysts for the low-temperature oxidation of carbon monoxide, benzene, and toluene

Three-dimensionally (3D) ordered mesoporous beta-MnO2-supported Au nanocatalysts (Au/beta-MnO2(urea), Au/beta-MnO2(NaOH), and Au/beta-MnO2(Na2CO3)) with an Au loading of 5 wt.% were prepared by the deposition-precipitation method using urea, NaOH and Na2CO3 as precipitating agent, respectively. The physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the complete oxidation of CO, benzene, and toluene. It is shown that the nature of precipitating agent had an important influence on the physicochemical properties of the beta-MnO2 support, Au nanoparticles, and Au/beta-MnO2 catalysts. Among the three Au/beta-MnO2 samples, the Au/beta-MnO2(NaOH) showed the highest surface atomic ratios of Mn3+/Mn4+, O-ads/O-latt, and Au3+/Au-0. The loading of gold could greatly modify the reducibility of Au/beta-MnO2 via the strong interaction between the gold and the beta-MnO2 support, and the Au/beta-MnO2(NaOH) sample possessed the best low-temperature reducibility. Gold loading resulted in a significant enhancement in catalytic activity of beta-MnO2. The three Au/beta-MnO2 catalysts outperformed the Au-free beta-MnO2 catalyst, among which the Au/beta-MnO2(NaOH) one showed the best catalytic activity (T-50% and T-100% = 48 and 70 degrees C for CO oxidation, 200 and 250 degrees C for benzene oxidation, and 170 and 220 degrees C for toluene oxidation, respectively). It is concluded that factors, such as the better gold dispersion, higher surface Au3+ and oxygen adspecies concentrations, better low-temperature reducibility, stronger synergistic action between the gold and the support as well as the high-quality 3D ordered mesoporous structure of the support, might be responsible for the excellent catalytic performance of Au/beta-MnO2(NaOH). (C) 2013 Elsevier Inc. All rights reserved.