Abstract
The size and morphology of palladium particles evaporated onto a SiO 2 film and deposited by impregnation on a porous SiO 2 support were examined by transmission electron microscopy (TEM) following sequential treatment on a gas mixture of 80% H 2, 20% H 2S at 523, 623 and 723 K. In model catalysts, progressive sulfidation of palladium from the surface to the bulk took place. By increasing the temperature in this process, coalescence and spreading of PdS particles was observed. In actual supported catalysts the same phenomenon was observed, but at higher temperature several particles appeared faceted with cubic shapes. The palladium real catalyst annealed in hydrogen at 673 K was found to be more active for the hydrodesulfurization of thiophene than those showing the sulfide phase. Also resistance to deactivation was unexpectedly high.
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