Preparation Of Au-Pd/meso-MO_x(M=Co,Cr) And Their Catalytic Performance For The Oxidation Of Typical Volatile Organic Compounds

Most of volatile organic compounds?VOCs? are harmful to the atmospherical environment and human health. Catalytic oxidation is one of the most effective pathways to eliminate VOCs, in which the key issue is the availability of effective catalysts. It is well known that cobalt oxides and chromium oxides are widely used in catalytic oxidation due to the presence of multivalent metal ions that lead to excellent catalytic performance. To the best of our known, there have been no reports on the applications of Au–Pd alloy nanoparticles?NPs? supported on meso-Cr₂O₃ or meso-Co₃O₄ for the oxidation of methane or toluene. In this thesis, we use the three-dimensionally mesoporous silica?KIT-6? as hard template to generate mesoporous Co₃O₄ or Cr₂O₃?denoted as meso-Co₃O₄ or meso-Cr₂O₃?, and adopted the polyvinyl alcohol?PVA?-protected reduction strategy to prepare the meso-Co₃O₄-or meso-Cr₂O₃-supported Au-Pd alloy NPs. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of methane or toluene. The relationship between physicochemical properties and catalytic performance of the materials has been established. The main results obtained in the thesis are as follows:1. The meso-Co₃O₄ and its supported Au, Pd, and Au-Pd alloy?x AuyPd/meso-Co₃O₄; x = 0.43-2.94 wt%; Au/Pd molar ratio?y? = 0.43-0.50? nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol?PVA?-protected reduction methods, respectively. It is found that the meso-Co₃O₄ with a high surface area of 106 m2/g was cubic in crystal structure and the noble metal nanoparticles?NPs? with a size of 2.7-4.5 nm were uniformly dispersed on the surface of meso-Co₃O₄. The 2.94Au0.50Pd/meso-Co₃O₄ sample performed the best for methane oxidation, showing the T10%, T50%, and T90%?temperatures required for achieving methane conversions of 10, 50, and 90%, respectively? of 230, 280, and 324 oC at a space velocity?SV? of 20,000 m L/?g h?, respectively, and the lowest apparent activation energy of 44.4 k J/mol. Furthermore, we found that the partial deactivation of 2.94Au0.50Pd/meso-Co₃O₄ due to CO₂ or H₂ O addition was reversible, but the introduction of SO₂ caused an irreversible deactivation of 2.94Au0.50Pd/meso-Co₃O₄. It is concluded that the excellent catalytic performance of 2.94Au0.50Pd/meso-Co₃O₄ was associated with its porous structure, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au-Pd alloy NPs and meso-Co₃O₄.2. The meso-Cr₂O₃ and its supported Au, Pd, and Au-Pd(0.90 wt% Au/meso-Cr₂O₃, 1.00 wt% Pd/meso-Cr₂O₃, and x Au₁Pd₂/meso-Cr₂O₃?x = 0.50-1.95 wt%? catalysts were prepared using the KIT-6-templating and PVA-protected reduction methods, respectively. It is found that the meso-Cr₂O₃ with a high surface area of 74 m2/g was rhombohedral in crystal structure and the noble metal nanoparticles?NPs? with a size of 2.9-3.7 nm were uniformly dispersed on the surface of meso-Cr₂O₃. The 1.95Au₁Pd₂/meso-Cr₂O₃ sample performed the best for the oxidation of toluene: the T10%, T50%, and T90% were 87, 145, and 165 oC at a SV of 20,000 m L/?g h?, respectively, and the apparent activation energy was the lowest?31 k J/mol? among all of the samples. The addition of moisture with a certain concentration was favorable for the improvement in catalytic activity of the 1.95Au₁Pd₂/meso-Cr₂O₃ sample. It is concluded that the excellent catalytic performance of 1.95Au₁Pd₂/meso-Cr₂O₃ was related to its small and uniform Au-Pd particles, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au-Pd NPs and meso-Cr₂O₃.