| Study on relationship between structure and property is the basis for the development of new catalyst. In this dissertation, Au-CeO2catalyst was prepared by adsorbed-layer nanoreactor technique (ALT). Based on the abundant regulation means of ALT, the relationship between structures and catalytic performances was investigated.The characteristic of nano-gold catalyst and its applications in low-temperature CO oxidation, pollution control, and green cheimsty were firstly reviewed. The effect of some important catalytic factors, such as size, valence, supporter, synthesis method was discussed. According to the research of nano-gold in catalytic combustion of volatile organic gases (VOCs), the most important factor, supporter, was announced. Based on the properties, such as excellent oxygen storage, promoting the dispersion of load particles, stabilizing active species and preventing carbon deposition, ceria became unreplaceable in the oxidation reaction system. Then, the new synthesis method used in this work named adorbed-layer nanoreactor technique was introduced. The research orientation and experiment were proposed.Based on the former research of the preparation of supported gold catalyst by ALT, the catalysts with different modifier were prepared. The results from TEM characterization and benzene oxidation (BO) activity measurement showed that, nano-CeO2with excellent redox properties facilitated forming highly dispersed Au, and special catalytic performance presented on CeO2/SiO2, which a conversion platform showed in320-470℃region. Herein, Au-CeO2system was more compatible for the the study of the catalytic performance of gold catalyst in BO.For better understanding of the special performance of nano cerium in BO, firstly, CeO2/SiO2preparaed by ALT and precipitation method were intercompared, and then the microstructure of the CeO2was regulated by calcination and alcohol-thermal treatment, the correspondingchanged catalytic properties were discussed. Size and microstructure of CeO2were determined by TEM and Raman spectorscopy. The results show that increasing the calcination temperature increased the particle size of cerium and reduced the content of the surface adsorbed superoxo, while alcohol-thermal treatment increased the type and content of the superoxo. The variation in superoxo content caused some corresponding changes in the conversion platform. The authors believe that benzene conversion platform could just showed on small cerium particles, the desorption of the adsorbed superoxo in a high-temperature reaction region induced the conversion platform.In order to study the influence of Au features on the catalytic properties of Au/CeO2/SiO2catalysts, the content, value and particle size of Au, which were determined by ICP-MS, XPS, TEM and XRD, were regulated by some designed experiments. The results showed that increasing Au content could reduce its dispersion, and the high-temperature activity was significant affected by Au, while the low-temperature activity was not. ALT and deposition-precipitation method were combined to gain catalyst with higher Au&+content, XPS indicated that Au&+content was39.4%, much higher than that (8.9%) of the catalyst prepared by ALT. The small changes in catalytic activity suggested valence of Au wasn’t the main factor. The size of Au were regulated by changing some parameters of preparation process, such as pH value, water concentraton, adsorption and reduction temperature of HAuCl4, aging temperature. The high-temperature activity of BO decreased with increasing in Au particle size,In order to study the influence of CeO2features on the catalytic properties of Au/CeO2/SiO2catalysts, the content, suface-property and grain structure of CeO2were regulated by some designed experiments. CeO2content was determined by ED AX and ICP-MS, and structure changes were determined by Raman spectroscopy. The results showed that the size of Au and the high-temperature activity were firstly decreased and then increased with increasing in CeO2content. At an extraordinary low CeO2content, the bad low-temperature-activity was acquired. Because the formation process of Au was pH-sensitive, the formation environmental was changed by pre-adding NaOH, aimed to regulating the structure and interaction of Au-Ce. This idea was verificated by the characterization and catalytic results:Raman spectroscopy indicated that moderately hydrolyzed HAuCl4induced remarkably red-shift of F2g peak of CeCl4by doping Au ions into CeO2grains. The redshift firstly increased and then decreased with increasing in content of pre-added NaON, induceing T10firstly increased and then decreased. The relationship between grain structure of CeO2and low-temperature activity in BO was ulteriorly viiified by the experiments of dopiong other ions.In conclusion, the authors suggested that the interaction between Au and CeO2was the key factor in BO, and the role of Au was different depending on reaction temperature:(1) at lower temperature, Au was doped into CeO2grains, inducing grain structure change and affecting the low-temperature activity;(2) at higher temperature, Au weaking Ce-O bond, reduing the reaction temperature of the surface lattice oxygen, which significantly affect the high-temperature activity of the catalyst.At last, the work in the dissertation was generalized, and the problems which still need to study were represented. |
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