Mendeleev
Communications
Mendeleev Commun., 2008, 18, 268–269
Dynamics of ethane transformation under redox conditions over
Pt/M O /Al O : effect of an oxygen storage component (M O )
x
y
2
3
x
y
Viktor V. Sinel’nikov, Galina O. Bragina, Nataliya S. Telegina,
Galina N. Baeva and Aleksandr Yu. Stakheev*
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 499 135 5328; e-mail: st@ioc.ac.ru
DOI: 10.1016/j.mencom.2008.09.014
Selectivity in ethylene was significantly improved by introduction of ZnO as an oxygen storage component into Pt/Al O catalyst
2
3
and alloying of Pt with Sn.
Oxidative transformation of light alkanes (C –C ) to valuable
H PtCl . The resulting materials were calcined at 600 °C (2 h)
2 6
1
3
–
1
products is one of the most important directions of research.
The process of ethane oxidative dehydrogenation (ODH) to
in air (300 ml min ). Further, the samples were reduced at
–1
400 °C (2 h) in H flow (100 ml min ).
2
1
ethylene is of significant industrial interest. However, there are
Before catalytic tests, we evaluated the oxygen storage capacity
of the catalysts by CO titration at 300, 350 and 400 °C. CO
titration experiments consisted of three stages. At the first stage,
the air was supplied and oxygen was accumulated on a catalyst
surface. On the next stage, the feed was replaced by nitrogen
for removing oxygen from gas phase. And, finally, the CO was
supplied. On this stage, the CO reacts with accumulated oxygen
and a catalyst OSC was measured on the basis of the amount of
a number of problems, which limit application of this process.
On one hand, hydrocarbon (ethane or ethylene)–air feed is
explosive. On the other hand, there is a considerable decrease
in selectivity at high ethane conversions due to a total oxidation
of ethane and ethylene by gas phase oxygen.
One of the promising approaches for improving selectivity of
ethane ODH consists in performing reaction under alternating
supply of an oxidant (air) and a hydrocarbon to a catalyst
CO formed.
2
(
redox conditions). At the first stage, oxygen is accumulated
Typical reaction cycle consisted of four stages: (i) catalyst
treatment in air for 200 s for surface oxygen accumulation;
(ii) purging in nitrogen for 50 s for removing gas phase oxygen;
(iii) ethane oxidation by accumulated oxygen for 400 s; (iv)
purging in nitrogen for 50 s for removing unreacted ethane and
reaction products from gas phase. Gas feed composition on the
ethane conversion stage was 17% C H in N . The catalyst
on a catalyst surface, and at the second stage the hydrocarbon
interacts with catalyst active sites and accumulated oxygen.
Previously, we observed the considerable decrease in total oxida-
tion products amount during propane ODH under redox condi-
2
tions. Hence, this method allows increasing selectivity of ethane
oxidative dehydrogenation due to a suppression of undesirable
total oxidation process in gas phase. Besides, the alternating
supply of oxygen and hydrocarbon eliminates danger of explo-
sion of the feed gas.
However, two main problems arise: (i) low efficiency due
to small oxygen storage capacity of the catalyst and (ii) low
activity in hydrocarbon oxidation of catalytic systems studied
so far. These drawbacks can be overcome by designing a dual-
2
6
2
sample (0.5 g) was held in place between two plugs of quartz
wool. Gas flow rate and GHSV were constant at all cycle stages
and equal to 200 ml min–1 and 12000 h , respectively. Reaction
temperature was 500 °C. Dynamics of variations of C H con-
–1
2
6
centrations and reaction products (CH , C H , CO, CO ) forma-
4
2
4
2
tion were monitored by on-line FTIR gas analyzer (GASMET
Dx-4000n).
3
function catalyst containing oxygen storage component (OSC)
The results of the OSC measurements by CO titration are
displayed in Table 1. The values allow us to rank samples in the
following order: Pt/CeO /Al O > Pt/ZnO/Al O > Pt/TiO /Al O >
and highly active dehydrogenation component (e.g., Pt).2
The main focus of this research consisted in elucidating
dynamics of ethane ODH and formation of the reaction pro-
ducts under conditions of alternating supply of reagents over a
catalyst. The catalysts studied contained Pt as dehydrogenation
component and a series of different metal oxides as oxygen
storage components (OSCs). The effect of OSC and alloying Pt
with Sn on the catalyst performances was evaluated.
2
2
3
2
3
2
2 3
> Pt/Al O .
2
3
Introduction of a metal oxide in Pt/Al O considerably increases
2
3
OSC of a system. Among the catalysts tested, the sample with
the CeO exhibited highest oxygen storage capacity (147 μmol
2
O per gramm of catalyst at 400 °C). The catalysts containing
2
ZnO and TiO are also promising since OSC for these systems
2
The 1% Pt/15% M O /Al O catalysts (where M O is CeO ,
is relatively high (> 70 μmol O per gram of catalyst).
x
y
2
3
x
y
2
2
ZnO, TiO , i.e. oxides of various metal types as an oxygen
2
Table 1 Effect of oxygen storage component on catalyst OSC.
storage component) were studied. Additionally, 1% Pt/Al O3
2
and 1% Pt–7% Sn/15% ZnO/Al O were studied. The parent
2
3
Oxygen storage capacity/
Al O (Sasol, Puralox NWa155) was used as received. Al O
2
3
2
3
μmol O per gram of catalyst
2
Catalyst
was loaded with 1 wt% Pt (from H PtCl ) and 15 wt% CeO or
2
6
2
300 °C
350 °C
400 °C
ZnO [from Ce(NO ) ·6H O or Zn(NO ) ·6H O aqueous solution,
3
3
2
3 2
2
respectively] by incipient–wetness coimpregnation. To produce
1% Pt/Al O
1% Pt/15% CeO /Al O
35
137
80
40
137
94
40
147
100
72
2
3
i
i
1
% Pt/15% TiO /Al O the Ti(OPr ) was diluted with Pr OH.
2
2
3
2
2
3
4
1% Pt/15% ZnO/Al O
2 3
Thus prepared solution was used for incipient–wetness impregna-
1% Pt/15% TiO /Al O
3
61
68
2
2
tion. Then, the TiO loaded carrier was impregnated with aqueous
2
©
2008 Mendeleev Communications. All rights reserved.
– 268 –
Sinel'nikov, Viktor V.
