| Most of volatile organic compounds(VOCs) and carbon monoxide are harmful to the atmospherical environment and human health. Catalytic oxidation is one of the most effective pathways to eliminate these harmful gases, in which the key is the availability of effective catalysts. It is well known that ceria-zirconia solid solutions possess good oxygen storage/release ability and good thermal stability, making them useful for the application in catalytic reactions. Doping Y3+ into the ceria-zirconia solid solution lattice, however, could result in the rises in oxygen vacancies and Ce3+ concentration. So far, there have been no reports on the applications of Au or Au–Pd alloy nanoparticles(NPs) supported on ceria–zirconia–yttria nanorods for the oxidation of toluene and/or carbon monoxide. In this thesis, we adopted the cetyltrimethyl ammonium bromide(CTAB)-assisted hydrothermal method to fabricate the Ce0.6Zr0.3Y0.1O2(CZY) nanorod support, and used the polyvinyl alcohol(PVA)-protected Na BH4 reduction method to prepare the CZY nanorod-supported nanosized gold(x Au/CZY, Au loading(x) = 0.4–4.7 wt%) and gold-palladium alloy(z Aux Pdy/CZY; z = 0.80–0.93 wt%; x or y = 0, 1, 2) NP catalysts. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of CO and/or toluene, so as to establish the relationship between physicochemical properties and catalytic performance of the materials. The main results obtained in this thesis are as follows:1. The CZY nanorods and their supported nanosized gold(x Au/CZY(x = 0.4, 0.9, 1.9, 4.7 wt%)) were prepared using the CTAB-assisted hydrothermal and PVA-protected Na BH4 reduction methods, respectively. It is shown that the CZY in x Au/CZY was cubic in crystal structure, surface areas of CZY and x Au/CZY were in the range of 68–79 m2/g, and the diameters of Au NPs well dispersed on the surface of CZY nanorods were 3.1–3.9 nm. The 4.7Au/CZY sample possessed the highest adsorbed oxygen species concentration and the best low-temperature reducibility, thus showing the highest catalytic activity:: the T50% and T90%(temperatures required for achieving reactant conversions of 50 and 90 %) were 32 and 60 oC for CO oxidation, and 218 and 265 oC for toluene oxidation at a space velocity of 20,000 m L/(g h), respectively. Introduction of water vapor with a lower concentration to the feedstock led to the partial deactivation of the 4.7Au/CZY sample, which was due to the competitive adsorption of H2 O and toluene as well as oxygen on the sample surface. The apparent activation energies(27–37 and 39–53 k J/mol) obtained over x Au/CZY were lower than those(42 and 88 k J/mol) obtained over CZY for CO and toluene oxidation, respectively. Based on the characterization results and activity data, it is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, highly dispersed Au NPs, and stronger interaction between Au NPs and CZY nanorods were the main factors influencing the catalytic performance of 4.7Au/CZY.2. The CZY nanorods and gold-palladium alloy(z AuxPdy/CZY; z = 0.80–0.93 wt%; x or y = 0, 1, 2) NPs were prepared using the CTAB-assisted hydrothermal and PVA-protected Na BH4 reduction methods, respectively. It is shown that the CZY in z Aux Pdy/CZY was of cubic crystal structure, surface areas of CZY and z Aux Pdy/CZY were 68–77 m2/g, and the Au-Pd NPs with a size of 4.6–5.6 nm were highly dispersed on the surface of CZY nanorods. Catalytically active sites might locate at the oxygen vancancies of CZY, oxidized noble metal NPs or the interfaces of noble metal NPs and CZY nanorods. Among all of the samples, 0.90Au1Pd2/CZY possessed the highest adsorbed oxygen species concentration and the best low-temperature reducibility, thus performing the best for toluene oxidation: the T50% and T90% were 190 and 218 oC at a space velocity of 20,000 m L/(g h), respectively. Introduction of water vapor with a lower concentration gave rise to a reversible partial deactivation of the 0.90Au1Pd2/CZY sample. The apparent activation energies(37–43 k J/mol) obtained over 0.90–0.93AuxPdy/CZY were much lower than that(88 k J/mol) obtained over CZY for toluene oxidation. It is concluded that the excellent catalytic performance of 0.90Au1Pd2/CZY was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, well dispersed Au–Pd NPs, and strong interaction between Au–Pd NPs and CZY nanorods. |
PDF Full Text Request