Abstract
Au was deposited on ultrastable Y (USY) zeolites using an ion-exchange method. Up to 5.5 wt% Au was introduced into the NH4-form of USY zeolites. In contrast, deposition of Au hardly took place on the H- and Na-forms of Y-type zeolites, NH4-forms of mordenite, and ZSM-5. Treatment of the Au-loaded USY zeolite in a H2 atmosphere, afforded Au0 nanoparticles. These particles were thermally stable even at 973 K, where their mean particle diameter was 3.7 nm. In contrast, highly aggregated Au particles were observed after thermal treatment at temperatures lower than 523 K, followed by storage in air for a month. The resulting particle sizes were in good correlation with the IR band intensity of the adsorbed CO and the catalytic activity of Au in the aerobic oxidation of benzyl alcohol. The Au nanoparticles showed highest activity when the Au/USY zeolite was thermally treated at 673–973 K. A negligible deactivation was observed after repeating the reaction at least 12 times. In the case of Au/TiO2 catalyst prepared by the deposition-precipitation method, the highest activity was observed at 573 K, which was lower than the temperature used for the Au/USY zeolites. This study demonstrated the potential use of the NH4-form of USY zeolites for supporting Au.
Highlights
Much attention has been paid to Au-loaded catalysts since the pioneering work done by Haruta and co-researchers [1,2]
Most of the Au present in the mother liquor was introduced into the NH4+-Y, CaNH4+-Y, and NH4+-ultrastable Y (USY) zeolites
The particle size of Au° generated through the thermal treatment of the
Summary
Much attention has been paid to Au-loaded catalysts since the pioneering work done by Haruta and co-researchers [1,2]. It has been reported that the catalytic activity of Au nanoparticles is sensitive to the preparation method and the type of support because it depends strongly on the size and shape of the. Earlier reports dealing with heterogeneous Au catalysts focused on the use of reducible metal oxides, such as TiO2 as a support for Au. To date, several methods, including deposition-precipitation [7], chemical vapor deposition [8], and cation adsorption [9], have been applied for the preparation of Au/TiO2 catalysts. Several methods, including deposition-precipitation [7], chemical vapor deposition [8], and cation adsorption [9], have been applied for the preparation of Au/TiO2 catalysts Among these methods, deposition-precipitation has been the most frequently employed method for Au loading, and it involves the use of tetrachloroauric (III)
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