Abstract
Pd was loaded on ultra stable Y (USY) zeolites prepared by steaming NH4-Y zeolite under different conditions. Heck reactions were carried out over the prepared Pd/USY. We found that H2 bubbling was effective in improving not only the catalytic activity of Pd/USY, but also that of other supported Pd catalysts and Pd(OAc)2. Moreover, the catalytic activity of Pd/USY could be optimized by choosing appropriate steaming conditions for the preparation of the USY zeolites; Pd loaded on USY prepared at 873 K with 100% H2O gave the highest activity (TOF = 61,000 h−1), which was higher than that of Pd loaded on other kinds of supports. The prepared Pd/USY catalysts were applicable to the Heck reactions using various kinds of substrates including bromo- and chloro-substituted aromatic and heteroaromatic compounds. Characterization of the acid properties of the USY zeolites revealed that the strong acid site (OHstrong) generated as a result of steaming had a profound effect on the catalytic activity of Pd.
Highlights
Heck reactions have been recognized as an important, useful and versatile methodology for the synthesis of aryl alkenes via arylation or vinylation of olefins
Structural Characterizations of ultra stable Y (USY) Zeolites Prepared Under Different Conditions
We found that Pd/USY worked very efficiently in Heck reactions when H2 bubbling was applied during reactions
Summary
Heck reactions have been recognized as an important, useful and versatile methodology for the synthesis of aryl alkenes via arylation or vinylation of olefins. Supported Pd catalysts are other candidates for use in Heck reactions, which compared to the homogeneous ones, are prepared and readily separated from the products. For this purpose, Pd has been supported on various materials, including activated carbon [5,6], zeolites [7,8,9,10] and polymers such as polyethylene glycol [11,12]. We tried to apply the Pd/USY catalysts in Heck reactions, focusing on the effects induced by continuous H2 bubbling during the reactions as well as the NH4-Y steaming conditions used to prepare the USY zeolite supports
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