Proton-type Zeolite Y Supported Gold Catalysts for Room-temperature CO Oxidation
Date Issued
2016
Date
2016
Author(s)
Chen, Yi-Hsiu
Abstract
Nanogold derived from chloroauric acid (HAuCl4) were deposited onto proton-type zeolite Y (HY) for catalyzing CO oxidation around room temperature. Three subjects were studied in this research. In the first part, the effect of surface modification on surface charge of proton-type zeolite Y (HY) was investigated. Owing to the negative zeta potential in neutral aqueous solution close to neutral, zeolite Y is not suitable for supporting negative-charge gold complexes. Nevertheless, the process of surface modification in NaNO3 solutions, with solution pH adjusted to 6 by NaOH(aq), was found able to reverse the zeta potential of HY to positive. In the second part of this study, the effect of surface charge of zeolite supports on the Au loading and catalytic activity was investigated. Positive correlation was observed between the surface charge and Au loading. For modified HY with positive surface charge, the supported gold species were with smaller sizes and finer dispersion. Through ESCA analyses, most of them were deposited near the exterior surface, which enables less resistance in mass transfer for CO oxidation. They possessed catalytic activity superior to those supported on HY without any surface modification. On the other hand, via lowering the solution pH to 2.6 (near IEP of zeolite supports), the surface charge can be reversed to positive as well. However, more residual Cl remained inside the catalysts. Moreover, gold species were deeply deposited inside the cages of HY. The as-prepared Au/Y possessed almost no catalytic activity. In summary, it is recommended to prepare Au/Y in aqueous solution at pH 6, with surface modified HY with positive surface charges. In the third part of this study, the effect of moisture on the catalytic activity of Au/Y was investigated. The results demonstrate that moisture is indispensable for Au/Y to maintain high catalytic activity. Under a relative humidity at ca. 30 % at 25 °C, Au/Y catalysts can perform the best activity in this research.
Subjects
Au/Y
CO oxidation
surface modification
surface charge
moisture
Type
thesis
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