Chemistry Reference
In-Depth Information
HDO, and a second site of molybdenum carbosulfide active for hydro-
genation, HDS and HDO. The catalyst was claimed to be promising for
different types of feedstock, including petroleum and coal-derived li-
quids. Dhandapani et al.
26
also studied g-Al
2
O
3
supported Mo
2
C with
phosphorus (P) as an additive. The catalyst was not tested for HDO, but
the P promoted catalyst showed higher activity for HDN. For HDS the ac-
tual procedure for adding P (prior to Mo, or co-addition) was found to have
an effect on the catalytic properties. A superior HDS catalyst was obtained
when the support was pretreated with P, which was claimed to be due to
reduced support-metal oxide interaction. Postreaction characterization
indicated that the catalysts were sulfur tolerant. The catalysts showed
higher activity than a conventional Ni-Mo-S/Al
2
O
3
(Shell 324) catalyst.
Dolce et al.
33
studied the hydrotreating activities of a series of g-Al
2
O
3
supported molybdenum carbides and nitrides (Mo loading range
3-11 wt%, which were synthesized by temperature programmed reaction
(CH
4
-H
2
and NH
3
, respectively) via the parent oxides. The catalyst activ-
ities were concluded to be competitive with commercial sulfide catalysts,
and several were considered promising for improving selectivity of
hydrogen pathways. The active domains were not visible with XRD even
at the highest Mo loading, which was interpreted as indicative of a high
dispersion. Free carbon was observed on the carbide catalysts, but be-
lieved to be caused by the support. The materials were tested for ben-
zofuran HDO, as well as quinoline HDN and benzothiophene HDS. It
appeared that HDO was not site specific over the nitrides and carbides.
Ramanathan and Oyama
40
studied a series of moderate surface area
(20-80 m
2
/g) metal carbides and nitrides of Mo, W, V, Nb and Ti, pre-
pared by temperature programmed reaction (20% CH
4
/H
2
and NH
3
, re-
spectively) of the parent oxide material. The materials were tested for
HDN (2000 ppm quinoline), HDO (500 ppm benzofuran), and HDS (3000
ppm dibenzothiophene), 20 wt% aromatics (tetralin) and balance ali-
phatics (tetradecane). The Mo
2
C showed superior activity on a surface
area basis compared to a commercial NiMo/Al
2
O
3
(Shell 324). The results
indicated that the materials possessed sulfur tolerance. A comparison of
HDO activities is shown in Fig. 7.
Nitrides. Ghampson, Fierro and coworkers have studied HDO of
guaiacol
194-196
as well as 2-methoxyphenol,
71
over various Mo
2
N based
catalysts. The effects of nitriding methods (H
2
/N
2
, vs. ammonolysis with
NH
3
), procedures and supports (activated carbons) were investigated.
195
It was found that H
2
/N
2
gave a better dispersion (of oxynitride) and also
higher activity. The mesoporosity of the carbon supports was found to be
favorable for HDO performance. Co was added as a co-metal, but did not
improve the observed properties. A comparison of the time-on-stream
behavior of unsupported Mo
2
N, NiMoS/Al
2
O
3
and Mo
2
N/GAC-NH is il-
lustrated in Fig. 8. The stability of the Mo
2
N catalysts appear as prom-
ising compared to the conventional system. Performance testing
indicated that the mechanism proceeded by direct demethoxylation, thus
bypassing the formation of catechol. The most active catalyst was MoN/
CGran-HN (The support "CGran" is an activated carbon from Norit
