Effect of Pd dispersion on methanol decomposition over supported Pd catalysts.

概要

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The turnover frequency (TF) for the methanol decomposition over various supported Pd catalysts is dependent upon both supporting materials and Pd crystallite sizes. On the other hand, the apparent activity (gas evolution rate per g-catalyst) is roughly proportional to the degree of Pd dispersion. This variation in the apparent activity is related to starting materials for the preparation of supports as well as to properties of supports. The highest dispersion of Pd was obtained with TiO2 prepared from Ti[OCH(CH3)2]4 or TiCl4, but at an elevated temperature (above 773 K) in the reduction treatment applied, it showed a suppressed activity. Pd particles on ZrO2 support gave a high value of TF when the Pd/ZrO2 catalyst was calcined in air at an elevated temperature (873–1073 K). The findings about the influence of heat treatment suggest that thermal stabilization of the ZrO2 support would play an important role in the development of catalytic properties of Pd. TF curves for the methanol decomposition over TiO2- and ZrO2-supported Pd catalysts change discontinously at about 10 Å of Pd particle size. In the case of Al2O3 support, characteristic behavior of TF curve are significantly different from those observed in the case of TiO2 and ZrO2 supports.
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