2
380
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001
Pirogova et al.
Table 6. Reduction of NOx to N2 over chromites supported
on γ-Al O *
respect to their activity in the same sequence as in the
oxidation reactions: ÑuCr O > MnCr O > CoCr O >
2
3
2
4
2
4
2
4
MgCr O > ZnCr O . The calcination temperature
2
4
2
4
Spinel
Tcal**
°C
NOx conversion (%)
at various temperatures (°C)
slightly affects the catalytic activity. The samples cal-
cined at 500 °Ñ are most active.
/
Thus, the supported chromites are bifunctional cata-
lysts, which accelerate both the oxidation of hydrocar-
1
50
200
250
300
350
CuCr O
350
38
46
56
25
20
23
18
37
36
26
16
18
15
24
33
5
49
59
29
23
25
19
34
39
31
17
20
18
28
38
7
51
59
31
24
28
21
35
40
45
17
20
20
28
40
7
51
59
33
25
30
20
17
20
22
32
41
8
bons and ÑÎ and the reduction of NÎ . As a rule, the
2
4
4
x
5
7
00
00
51
20
17
20
17
22
32
20
16
15
12
18
25
4
catalysts containing Mg2+ or Zn2+ cations are less active
2+
2+
than complex chromites containing cations Mn , Co ,
CoCr O
350
2
2+
and Cu . The oxides containing two transition ele-
5
7
00
00
ments including chromium are more active. The calci-
nation temperatures of 350500 °C are preferable in the
catalyst preparation.
MnCr O
350
2
4
5
7
00
00
ZnCr O
350
2
4
References
5
7
00
00
MgCr O
350
1. G. I. Alkhazov and L. Ya. Margolis, Glubokoe kataliticheskoe
okislenie organicheskikh veshchestv [Deep Catalytic Oxida-
tion of Organic Substances], Khimiya, Moscow, 1985, 186 pp.
2
4
5
7
00
00
(
in Russian).
*
Composition of exhaust gas (%): N , 60.9; NO , 5.2; CO, 6.8;
2 x
2. D. V. Sokol´skii and N. M. Popova, Kataliticheskaya
ochistka vykhlopnykh gasov [Catalytic Refinement of Exhaust
Gases], Nauka, Alma-Ata, 1970, p. 28 (in Russian).
O , 19 (without CHx and H O).
*
2
2
* See note* in Table 2.
3
. G. N. Pirogova, N. M. Panich, R. I. Korosteleva, Yu. V.
Tyurkin, and Yu. V. Voronin, Izv. Akad. Nauk, Ser. Khim.,
second above 300 °C. In the low-temperature region,
o-xylene slightly undergoes partial oxidation to TA and
some deep oxidation along with adsorption. At the
temperature of least ∼ 300 °C , deep oxidation prevails.
The position of this high-temperature region depends on
1
994, 1730 [Russ. Chem. Bull., 1994, 43, 1634 (Engl.
Transl.)].
4. G. N. Pirogova, N. M. Panich, R. I. Korosteleva, Yu. V.
Voronin, and N. N. Popova, Izv. Akad. Nauk, Ser. Khim.,
2
000, 1547 [Russ. Chem. Bull., Int. Ed., 2000, 49, 1536].
. V. I. Varlamov and V. S. Komarov, Zh. Prikl. Khim.,
985, 58, 2355 [J. Appl. Chem. USSR, 1985, 58 (Engl.
Transl.)].
5
the spinel nature: for CuCr O , CoCr O , and MgCr O
4
2
4
2
4
2
1
it begins from 280, 310, and 300 °Ñ, respectively.
To study the reduction of nitrogen oxides to N , we
2
6. D. T. Sviridov, R. K. Sviridova, and Yu. F. Smirnov,
Opticheskie spectry perekhodnykh metallov v kristallakh [Op-
tical Spectra of Transition Metals in Crystals], Nauka, Mos-
cow, 1976, p. 102 (in Russian).
used a real exhaust gas containing N , Î , ÑÎ, ÑÎ ,
2
2
2
NÎ , and CH . Oxides NÎ are reduced according to
x
x
x
the reaction
7
. V. A. Shvets and V. B. Kazanskii, Kinet. Katal., 1966, 7,
712 [Kinet. Catal., 1966, 7 (Engl. Transl.)].
. L. K. Przheval´skii, V. A. Shvets, and V. B. Kazanskii,
Kinet. Katal., 1970, 11, 1310 [Kinet. Catal., 1970, 11 (Engl.
Transl.)].
2
CO + 2 NO → 2 ÑÎ + N .
2 2
8
Several reactions proceed simultaneously, and the
most important of them is CO oxidation.10 The ratio
9
. N. Mizuno, Catal. Today, 1990, 8, 221.
between CO oxidation and NÎ reduction depends on
the oxygen concentration. At the oxygen excess, the
x
1
0. R. A. Gazarov, V. A. Matyshak, and M. M. Slin´ko, Itogi
nauki i tekhniki, Ser. Kinetika i kataliz [Scientific Results,
Kinetics and Catalysis], VINITI, Moscow, 1986, 15, 3 (in
Russian).
oxidation of CÎ and CH , proceeds predominantly, and
x
at the small oxygen content, CO is consumed to reduce
NÎ . The findings of the runs on NÎ reduction are
x
x
presented in Table 6. As in oxidation, CuCr O is most
active. The chromites studied can be arranged with
Received April 16, 2001;
in revised form June 18, 2001
2
4