Developing Processes for Preparing Nano-gold Catalysts (Au/TiO2) at Room Temperature
Date Issued
2010
Date
2010
Author(s)
Tsai, Wei-Ming
Abstract
In the past the processes for the deposition of gold species on TiO2 surface developed in different research laboratories were usually carried out at solution temperatures higher than 60°C in a state of good mixing. However, when it is applied in the large scale production, the good mixing in order to maintain uniform temperature in the whole solution system is a challenge in engineering. Moreover, rising the solution temperature consumes energy. Therefore, there is a need to develop the deposition process around room temperature. Although the room temperature prepared catalysts contain substantial amount of residual chloride, which poisons the active sites for the catalytic activity, the drying under saturated water vapor pressure process can not only improved the catalytic activity but also maintained the gold loading. It has been found in this research that the drying at different saturated steam temperatures influences the catalytic activity. Furthermore, drying under steam at the temperature above 50°C was more effective, in contrast to drying below 50°C. The catalyst dried under steam at 80°C and followed by the washing process possessed the highest CO conversion among all the RT-prepared Au/TiO2 in this research. The resulting Au/TiO2 possessed activity as high as those from the deposition processes in the solution at 80°C. On the other hand, it is confirmed from the analyses by using ionic chromatography that drying under steam at 80°C can break Au and Cl bond of gold species remaining on Au/TiO2 prepared at room temperature. The chloride on catalyst surface can be removed easily by the later washing process. Nevertheless, the catalyst which was dried below 50°C can not break the bond of Au-Cl effectively. The remaining chloride still causes the lower catalytic activity of Au/TiO2.
In order to cost down the price of raw materials of gold for making Au/TiO2, the gold plate or the gold powder was dissolved in aqua regia. The solution was used for deposition of gold species on TiO2 at room temperature. The post treatments under steam and of washing for removing chloride were also applied. It is found in this research that the as-prepared catalysts possess lower catalytic activities than that prepared from gold solution, which was dissolved from HAuCl4 purchased from Merck. The residual nitrate on the catalysts from aqua regia solution may be the main cause for the lower catalytic activity.
Subjects
nano-gold catalysts
TiO2
CO oxidation at low temperature
room temperature procedure
residual chloride
Type
thesis
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