A. Aguirre-Gutiérrez et al. / Journal of Molecular Catalysis A: Chemical 346 (2011) 12–19
19
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
mentioned that most of the previous papers reported no gain of
catalytic activity when Pd was incorporated in the oxide state to
NiMo or NiW catalysts supported on alumina. The anatase phase is
recognized to prevent Ni migration into the support and it has also
been reported that it exerts a positive electronic interaction with
Pd [27].
4. Conclusions
4,6-DM-BCH
3,3'-DM-CHB
3,3'-DM-BP
The addition of Pd and Ni over the Mo/AT had a positive effect
and produced highly active sulfided catalyst for hydrodesulfuriza-
tion of the highly refractory 4,6-DMDBT molecule by enhancing
both the hydrogenation and hydrodesulfurization pathways. There
was found a synergetic effect of Pd and Ni on the Mo/AT catalyst, but
it is higher when Pd is incorporated on NiMo/AT catalyst than when
Pd is incorporated on Mo/AT catalyst. From our results, since Pd
promoted the HDS activity for a NiMo system, the alumina–titania
support played an outstanding role over the incorporation to Pd to
the active phases.
4,6-DM-TH-DBT
0.0
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
Xa %
Fig. 11. Products distribution (yield%) for 4,6-dimethyldibenzothiophene
hydrodesulfurization reaction over the PdNiMo/AT sulfided catalyst.
ination (HYD) was slightly higher than 3,3ꢀ-DM-BP (DDS) for both
catalysts. The complete saturated and desulfurized 3,3ꢀ-DM-BCH
Mo/AT catalysts did not show any significant differences in product
yields as compared with the Mo/AT sample (figure not shown).
For the NiMo/A and NiMo/AT catalysts the product distribu-
tion patterns are shown in Fig. 10. One can notice significant
differences with those for the unpromoted systems. For both
catalyst the main compound produced was the desulfurized 3,3ꢀ-
DM-CHB (HYD). According to the literature [2] this compound
comes basically from the C–S cleavage of the partially hydrogenated
4,6-DM-TH-DBT compound, which suggests that the main effect
of the 4,6-DM-TH-DBT intermediate. Furthermore, the DDS route
was also favored for the NiMo samples as higher production for
3,3ꢀ-DM-BP was observed. However product yields for the HYD
pathway were higher than the DDS pathway. Fig. 11 shows that
the PdNiMo/AT catalyst presents a very similar distribution product
pattern throughout the reaction as the NiMo catalysts. Never-
theless a slightly higher yield for 3,3ꢀ-DM-BCH (HYD) compound
was noticed at conversions up to 50% while the 4,6-TH-DMDBT
decreased.
From catalytic properties results it appeared that Pd did not
enhance either the activity or selectivity for Mo supported on
alumina–titania and it can be explained in terms of a lack of
promotion of Pd over MoS2 sites. From Raman Spectroscopy on
the calcined samples, MoOx species were not modified and XRD
showed significantly larger particles than for NiMo/AT. Moreover,
stacking and length of MoS2 crystallites determined from HRTEM
results, did not vary after Pd addition and Pd particles were not
detected by this technique. These results suggest that Pd could be
well dispersed on the alumina–titania surface without any signifi-
cant electronic interaction with the MoS2 phase. By contrast, XRD
and Raman results pointed out to a different interaction between Pd
and the NiMo/AT system. Firstly, MoOx particles exhibited smaller
particles which were almost completely sulfided. Secondly, HRTEM
images showed an increase in order and stacking after Pd addition
as compared with Mo/AT. Finally, the total hydrodesulfurization
capacity for the PdNiMo/AT was higher than that for Mo/AT and
NiMo/AT, suggesting a close interaction of Pd with NiMo. Fur-
thermore, since Pd promoted the HDS activity for a NiMo system
supported on AT as compared with an equivalent catalyst sup-
ported on A, the support played an important role. It should be
Acknowledgements
Aguirre gratefully acknowledges IMP, Mexico, for providing the
financial support through the Postgraduate Program.
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