| dc.description.abstract | Rice husk ash-supported copper catalysts including both unpromoted (Cu/RHA) and Cr2O3 - promoted (Cu/Cr/RHA) ones, which were prepared by incipient wetness impregnation, have been investigated in two parts of this dissertation, respectively. Surface characterization by XRD(X-ray diffraction), TGA (thermogravimetric analysis), TPR (temperature-programmed reduction), SEM(scanning electronic microscopy), and H2-N2O titration, and catalytic activity by ethanol dehydrogenation have been examined extensively.
The results derived from each part will be described as follows:
1. For the preparation of Cu/RHA catalysts: TGA results reveal that both the unsupported and RHA-supported precursors having been derived from copper nitrate trihydrate are completely converted to cupric oxide above ca. 600 K. The XRD patterns and SEM images show that higher copper loading leads to the agglomeration of CuO crystallites. The TPR profiles denote the probable existence of both CuO and Cu2+ in the calcined copper catalysts. CuO exhibits weak metal-support interaction (MSI) while Cu2+ in much lower content exhibits strong MSI. Ethanol conversion and turnover frequency (TOF) show little dependence on copper loading. Ethanol conversion increases with an increase in reaction temperature. Furthermore, copper catalysts supported on rice husk ash display higher catalytic activity than those supported on silica gel, as revealed by the test of ethanol dehydrogenation. Calcination temperature around 723 K, giving a high initial activity and a low deactivation rate, seems to be an optimal condition for manufacturing Cu/RHA catalyst precursors in this work.
2. For the preparation of Cu/Cr/RHA catalysts: Copper dispersion can be enhanced by the initial increase in Cr2O3 promoter content up to 2 wt%, while it then deteriorates gradually upon further increase in promoter content. It has been suggested that an optimal Cr content around 2 wt% not only enhances catalytic activity but also retards catalyst deactivation. Generally speaking, catalyst deactivation results predominantly from copper sintering. Despite of the lower BET surface area, RHA is superior to commercial silica gel as a candidate for catalyst support in this work, because the surface of the former may possess more unique pores, while the majority of surface pores on the latter are interconnected and clogged easily. | en_US |