Au–Ag/CeO2 and Au–Cu/CeO2 Catalysts for Volatile Organic Compounds Oxidation and CO Preferential Oxidation

Abstract

Oxidation of volatile organic compounds (VOC) and preferential oxidation of CO in the excess of H 2 (CO-PROX) were investigated over mono and bimetallic Au-Ag/CeO 2 and Au-Cu/CeO 2 catalysts. For the oxidation of VOC (2-propanol, ethanol and toluene) Au/CeO 2 was the most active catalyst for the combustion of alcohols to CO 2 , Ag/CeO 2 gave the best performance in the toluene total oxidation, Au-Ag/CeO 2 and Au-Cu/CeO 2 showed the highest selectivity to partial oxidation products. For CO-PROX Au-Ag/CeO 2 and Au-Cu/CeO 2 samples exhibited higher CO 2 yield at low temperature than monometallic ones. The improved performance of bimetallic catalysts were accounted for an enhancement of surface ceria oxygens mobility caused by the addition of Ag or Cu to Au/ CeO 2 and involved in both investigated reactions. This effect was more evident on Au-Ag/CeO 2 where a strong Au-Ag interaction occurred with formation of Au-Ag alloy or linked monometallic nanoparticles. Graphical Abstract

Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation

“…The deconvolution of the Ru-Pd/CeO 2 -MnO x reduction peak ( Figure S1B) revealed two other contributions, one at low temperature (140 • C) and one at high temperature (275 • C), probably due to the reduction of part of the metal precursors. It is possible in this case, in the same way as other bimetallic systems supported on cerium oxide reported in the literature [6,12], that a mutual interaction between the two metals leads a single reduction peak, distinct from the individual monometallic samples. Furthermore, this reduction peak being shifted at lower temperature than the monometallic Ru sample also suggests an increased reducibility/mobility of the ceria-manganese reactive oxygens [6,12,40].…”

“…This happens also for selectivity to CO 2 ( Figure 1c). To comprehend this behavior, the fact that cerium oxide has a strong tendency to provide active oxygens with strong oxidation power [6,12,25,26], which are however reactive towards both CO and H 2 , must be taken into account. This causes a drop of selectivity at higher temperature due to the higher activation energy of H 2 oxidation compared to that of CO [27][28][29][30].…”

“…It must be stressed that the increased activity of the Ru-Pd system cannot be related to the concentration of the metal species, which on both mono and bimetallic samples remains 1 wt % (0.5-0.5% on bimetallics and 1% on monometallics). It has been seen that bimetallics can be often better performing than the related monometallics due to a synergy between the two metals and/or the support [6,12,31]. …”

“…The series of peaks at 900.5, 906.9 and 916.2 are the related spin-orbit components of the 3d 3/2 states of the same configurations. Moreover, there is no structure between the peaks at 882.0 eV, 888.6 eV and 897.9 eV, and this rules out any 3d 9 4f 1 (O 2p 6 ) Ce 3+ final state [61].…”

“…Recently, the use of a reducible/active support, such as cerium oxide or iron oxide, resulted in remarkably low-temperature CO-PROX activities [12,17]. The peculiar red-ox properties of CeO 2 involving the facile exchange between Ce 3+ and Ce 4+ states and the high mobility of O 2-ions in the lattice, are the key factors to explain the high relevance of this oxide as a metal support in the PROX reaction [6,12,13,18].…”