Novel supported catalyst for hydrodesulfurization reaction

Article abstract of DOI:10.1039/a807002d

Thanks to a combination of the high activity of ruthenium and unique properties of a new support, magnesium fluoride, a system highly active in the hydrodesulfurization reaction was obtained.

Full text of DOI:10.1039/a807002d

Novel supported catalyst for hydrodesulfurization reaction
Maria Wojciechowska,* Mariusz Pietrowski and S /l awomir /L omnicki
A. Mickiewicz University, Faculty of Chemistry, 60-780 Pozna n´ , ul. Grunwaldzka 6, Poland.
E-mail: emawoj@main.amu.edu.pl
Received (in Cambridge, UK) 18th September 1998, Accepted 20th January 1999
Thanks to a combination of the high activity of ruthenium
and unique properties of a new support, magnesium
fluoride, a system highly active in the hydrodesulfurization
reaction was obtained.
The petrochemical industry faces a difficult problem of
satisfying increasingly restrictive standards for fuels. In partic-
ular this problem concerns the reduction of the content of sulfur,
nitrogen and aromatic components in the fuels produced, which
can be achieved by application of various hydrotreatment
processes of crude fuels (HDS, HDN, HDM, HYD and HYC).
The sulfided catalysts applied at present, containing molybde-
num, cobalt, nickel and tungsten supported on alumina will not
be able to comply with future standards of fuel quality. Thus it
is necessary to prepare new catalysts for hydrotreatment, which
apart from high activity, should be characterized by high HDS
selectivity.
In 1981, Pecoraro and Chianelli1 showed that among
transition metal sulfide catalysts, ruthenium systems were the
most active. Further studies revealed the dependence of activity
of sulfided ruthenium catalysts and the support used. For
example Ru supported on alumina2 was found to have
different HDS properties than Ru supported on carbon.4
,3
The present results concern thiophene HDS activity at
atmospheric pressure. Thiophene was introduced into the
reactor by bubbling a stream of pure hydrogen at a rate of 15
2 2 3
Fig. 1 Comparision of the HDS activity over Ru/MgF (MRu), Ru/Al O
(AlRu) and Ru/SiO (SiRu) catalysts at 400 °C. S, sulfided in 10% H S–H ,
2
2
2
2 2
400 °C, 2 h; OS, calcined in air at 400 °C, 4 h, sulfided in 10% H S–H ;
3
21
400 °C, 2 h. The rate of HDS of thiophene is given by HDS rate = FXC/W,
where F is the total flow rate of feed, X the fractional conversion, C the
concentration of thiophene in the feed and W the catalyst weight.
cm min through a thiophene saturator, maintained in an ice
bath at 0 °C. The concentration of thiophene in the feed steam
3
21
24
(
total flow rate 20 cm min ) was maintained at ca. 2.5 3 10
2
1
mol l by adjusting the H
2
flow rate through the saturator. The
gas mixtures were analyzed by on-line gas chromatography.
The Ru/MgF catalysts were prepared by conventional
impregnation with Ru (CO)12, surface area of the support =
0 m g . Magnesium fluoride was obtained from the reaction
2
3
2
21
4
5
3
of MgCO with a 1:1 aqueous solution of HF. The precipitate
was then dried at 110 °C for 24 h and calcined in air at 400 °C
for 4 h. The specific properties of magnesium fluoride:
hardness, resistance to calcination in oxygen and well devel-
oped porous structure enable its application as an active support
and owing to the absence of lattice oxygen anions, opens up
great possibilities for the study of the structure and texture of the
catalyst5 as well as reaction mechanisms.7,8 Additionally the
presence of anions of higher electronegativity than oxygen
anions leads to the expectation of the appearance of strong
interactions between the support and the supported active
phase.
,6
2
The Ru/MgF system containing 1.61% weight of ruthenium
was found to be more active than similar samples supported on
alumina or silica (Fig. 1). All samples were pretreated in two
ways: S, sulfidation in 10% H
air followed by sulfidation in 10% H
2
S–H
2
and (ii) OS, calcination in
S–H
2
2
.
As can be seen in Fig. 1, preliminary calcination in air
distinctly increases the activity of the samples (apart from those
supported on silica). This effect can be explained by much
easier sulfidation of calcined samples, which proceeds by the
exchange of surface oxygen ions of RuO
atoms.
2
clusters by sulfur
2
Fig. 2 Product distribution of thiophene HDS over Ru/MgF (MRu) and Ru/
Fig. 2 presents the product distribution of thiophene HDS
over Ru/MgF and Ru/Al . The selectivity of hydrogenation
Al O3 (AlRu) catalysts. S, sulfided in 10% H S–H , 400 °C, 2 h; OS,
calcined in air at 400 °C, 4 h, sulfided in 10% H S–H , 400 °C, 2 h.
2 2
2
2
2
2
O
2 3
Chem. Commun., 1999, 463–464
463

Table 1 Selectivity of hydrogenation and isomerization
H2
H2
+
Sample
S
hyd
S
iso
–H2S
S
MRu-S
MRu-OS
AlRu-OS
0.00
0.00
0.06
1.00
0.94
0.36
Scheme 1
The catalytic tests for model catalytic reactions of the
described samples show a correlation between the thiophene
HDS activity and the number of medium strength acidic sites.
(Shyd) is defined as the ratio of the formation rates of butane vs.
butenes, whereas the ratio of but-1-ene vs. but-2-enes represents
the selectivity of isomerization (Siso).
From the above data the conclusion can be made that Ru/
Notes and references
MgF
much less hydrogenation occurs simultaneously with hydro-
desulfurization (Table 1) in comparison with Ru/Al . This,
together with very high HDS activity is a clear advantage of Ru/
MgF catalysts compared with other ruthenium systems sup-
2
catalysts are very selective systems in the HDS process,
1
2
3
4
T. A. Pecoraro and R. R. Chianelli, J. Catal., 1981, 67, 430.
M. Nagai, K. Koizumi and S. Omi, Catal. Today, 1997, 35, 393.
Y. J. Kuo and B. J. Tatarchuk, J. Catal., 1988, 112, 229.
2 3
O
M. J. Ledoux, O. Michaux and G. Agostini, J. Catal., 1986, 102, 275.
2
5 J. Haber and M. Wojciechowska, J. Catal., 1988, 110, 23.
6 J. Haber and M. Wojciechowska, Catal. Lett., 1991, 10, 271.
7 M. Wojciechowska, J. Haber, S.
in press.
ported on different supports.
9
Since the work of Ledoux at al. and Qusro and Massoth,10
/L omnicki and J. Stoch, J. Mol. Catal.,
which found a distinct correlation between the HDS activity of
thiophene and dibenzothiophene, the results of the HDS
reaction for thiophene can be a model example for general
8
M. Wojciechowska, J. Haber and S.
997, 23, 7.
M. J. Ledoux, C. P. Huu, Y. Segura and F. Luck, J. Catal., 1990, 121,
0.
/L omnicki, Arch. Environ. Protect.,
1
9
conclusions of the hydrodesulfurization activity of the Ru/MgF
system.
2
7
1
1
0 Q. Qusro and F. E. Massoth, Appl. Catal., 1987, 29, 375.
1 K. F. McCarthy and G. L. Schrader, J. Catal., 1987, 103, 261.
The lack of tetrahydrothiophene in the reaction products
together with the presence of buta-1,3-diene suggests the
reaction pathway shown in Scheme 1.11
Communication 8/07002D
464
Chem. Commun., 1999, 463–464