SYNTHESIS, CHARACTERIZATION AND APPLICATIONS OF NANOSTRUCTURED MATERIALS AS NOVEL CATALYST SUPPORTS IN ETHANOL REFORMING FOR HYDROGEN PRODUCTION

Abstract

The recent synthesis and applications of oxide nanotubes and mesoporous materials attract intense research interests due to their chemical and physical properties. This thesis reports the synthesis and characterization of Rh supported on nanostructured materials, such as oxide nanotubes and mesoporous materials, and their applications as highly active and stable catalysts for H2 production in steam reforming of ethanol (SRE) and CO2 reforming of ethanol (CRE). A fundamental understanding of the cause of the high activity and the stability of Rh/oxide-nanotube catalysts has also been studied in this work. SRE is regarded as an effective and important method for H2 production since the hydrogen in steam not only could be transformed to H2 gas but also could minimize coke formation. Among the four Rh-based catalysts investigated, Rh/Y2O3 was found to show excellent catalytic performance for H2 production in SRE. Some related factors have also been investigated to determine the key factor causing the different catalytic performance of the four Rh-based catalysts in SRE. Furthermore, a novel Rh/Y2O3-nanotube catalyst has also been developed and found to have even higher H2 production rate than Rh/Y2O3 in SRE due to the anti-sintering of Rh species on Y2O3 nanotubes. Some of the significant findings of this research in SRE are as follows: (1) The strong oxidising ability of Y2O3 is found to be the key factor underlying the high activity and stability of Rh/Y2O3, suggesting a strong relationship between the oxidizing ability of the catalyst support and its catalytic performance; (2) A new indicator, H2/C, has been proposed in this study, for the first time, and it was found to have a strong linkage to the optimal H2 production rate under the lowest C emission in SRE; (3) the anti-sintering property of Y2O3 nanotubes was discovered for supported metal catalyst and this has significant influence on the catalyst¿s performance. CRE has been considered as one of the important methods to solve the global warming as CRE involves CO2, which is a greenhouse gas, and ethanol, which is a renewable source. A series of Rh supported on Ce-SBA-15 catalysts, which have unique nanopores, have been synthesized and applied as CRE catalysts. Since Ce is found to promote the low catalytic activity of SBA-15 silica support, CeO2 nanotubes are then developed and applied, for the first time, as the novel catalyst support. A novel Rh/CeO2-nanotube catalyst, synthesized in this study, is found to show an excellent H2 production rate and ethanol conversion in CRE due to the versatile and remarkable redox properties of Rh on CeO2 nanotubes. Some of the significant findings of this research in CRE are as follows: (1) The oxygen mobility of SBA-15 can be significantly improved by the incorporation of Ce in the framework of SBA-15; (2) The redox properties of Rh play a key factor in the high activity and stability of Rh/CeO2-nanotube catalyst in CRE, suggesting the importance of redox properties to catalytic performance in CRE. (iii) A reaction mechanism for CRE based on the redox properties over Rh/CeO2-nanotube catalyst has been proposed.