Preparation Of Supported Gold-palladium Alloy Nanocatalysts And Their Catalytic Performance For The Oxidation Of Hydrocarbons

Most of volatile organic compounds?VOCs?are not only detrimental to the environment but also harmful to human health.Catalytic oxidation is considered to be one of the most effective methods for the removal of VOCs.The key issue of this technology is the development of effective catalysts.Cobalt chromate?CoCr₂O₄?exhibits excellent high-temperature stability and sulfur-resisting performance,and thus is widely used for methane combustion.Transition-mental oxides?e.g.,Co₃O₄?are used as catalyst for the removal of VOCs due to low cost and relative abundance.In this thesis,the polymthyl methacryalate?PMMA?colloidal crystal-templating and molten salt methods were employed to fabricate the three-diemnsionally macroporous?3DOM?CoCr₂O₄ and octahedron-like Co₃O₄ supports,respectively.The polyvinyl alcohol?PVA?-protected reduction method was used to prepare the xAu Pd_y/3DOM CoCr₂O₄?x=0.98 and 1.93 wt%;Pd/Au molar ratio?y?=1.93 and 1.95?and xAuPd_y/Co₃O₄?x=0.18,0.47,and 0.96 wt%;Pd/Au molar ratio?y?=1.85,1.93,and1.92?catalysts.Physicochemical properties of the samples were characterized by means of numerous analytical techniques,and their catalytic activities were evaluated for the oxidation of methane and typical VOCs?e.g.,toluene and o-xylene?.The relationship between physicochemical properties and catalytic performance of the materials has been established.The main results obtained in the thesis are as follows:1.3DOM CoCr₂O₄ and its supported Au-Pd alloy?xAuPd_y/3DOM CoCr₂O₄;x=0.98 and 1.93 wt%;Pd/Au molar ratio?y?=1.93 and 1.95?nanocatalysts were prepared using the PMMA-templating and PVA-protected reduction methods,respectively.The 3DOM CoCr₂O₄ and xAuPd_y/3DOM CoCr₂O₄ samples possessed a high-quality 3DOM structure and a surface area of 33-36 m²/g.The Au-Pd alloy nanoparticles?NPs?with an average size of 3.3 nm were uniformly dispersed on the surface of the 3DOM CoCr₂O₄ support.The 1.93AuPd_1.95/3DOM CoCr₂O₄ sample showed the best catalytic performance:the T_10%,T_50%,and T_90%?temperatures required for achieving methane conversions of 10,50,and 90%,respectively?were305,353,and 394 ^oC at a space velocity?SV?of 20,000 m L/?g h?.The introduction of water vapor or sulfur dioxide to reaction system could influene the catalytic activity of 1.93AuPd_1.95/3DOM CoCr₂O₄,among which the deactivation of the sample induced by water vapor addition was reversible.It is concluded that the excellent catalytic performance of 1.93AuPd_1.95/3DOM CoCr₂O₄ was associated with its higher surface area and adsorbed oxygen species concentration,better low-temperature reducibility,and strong interaction between Au-Pd alloy NPs and 3DOM CoCr₂O₄.2.The octahedron-like Co₃O₄ and its supported Au-Pd?xAuPd_y/Co₃O₄;x=0.18,0.47,and 0.96 wt%;y?Pd/Au molar ratio?=1.85,1.93,and 1.92?nanocatalysts were prepared using the molten salt and PVA-protected reduction methods,respectively.It is found that the molten salt-derived Co₃O₄ sample displayed a well-defined octahedron-like morphology with an edge length of 300 nm.The Au-Pd NPs with a size of 2.7-3.2 nm were highly dispersed on the surface of octahedron-like Co₃O₄.The 0.96AuPd_1.92/Co₃O₄ sample exhibited better catalytic activity,and the T_90%was180 and 187 ^oC for toluene and o-xylene oxidation at SV=40,000 m L/?g h?,respectively.It is concluded that the good catalytic performance of octahedron-like Co₃O₄-supported Au-Pd nanocatalysts was related to the strong interaction between Au-Pd NPs and octahedron-like Co₃O₄ and the higher adsorbed oxygen species concentration.