Hydrodesulfurization of
Dibenzothiophene over MCM-41-Supported
Pd and Pt Catalysts
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Abstract
Three series of aluminosilicate MCM-41 (Al-MCM-41) were
synthesized
using different aluminum sources, including aluminum isopropoxide
(AlM-I), pseudoboehmite, and aluminum sulfate, by a hydrothermal method.
The hydrodesulfurization (HDS) performance of the Al-MCM-41-supported
Pd and Pt catalysts prepared with chlorided precursors were evaluated
with dibenzothiophene (DBT) as the model sulfur-containing molecule,
in comparison with those supported on a siliceous MCM-41 (SiM). Pd/SiM
and Pt/SiM were not promising for DBT HDS because of their relatively
low activities and the rapid irreversible deactivation. Pd and Pt
supported on the acidic Al-MCM-41 materials showed higher dispersion
and enhanced HDS performances. AlM-I, which possessed the strongest
acidity, was the most promising among the mesoporous materials investigated.
The deactivated Pd/AlM-I and Pt/AlM-I can be reversibly regenerated
by H<sub>2</sub> reduction. DBT HDS over the Pd catalysts predominantly
took the hydrogenation (HYD) pathway, whereas the direct desulfurization
(DDS) pathway and HYD pathway were comparable for the Pt catalysts.
Increasing the support acidity had no positive effect on the DDS activity
of Pd but significantly enhanced its HYD activity, while the increase
in the rate constant of DDS pathway was close to that of the HYD pathway
for Al-MCM-41-supported Pt catalysts. The effect of the acid properties
of the supports on the HDS performance of Pd and Pt catalysts was
discussed by considering the formation of “electronic-deficient”
particles and the hydrogen spillover process
