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31Influence of the crystallinity degree of cobalt-containing catalysts on their activity...
Section 2. Kinetics and catalysis
Abuzarli Farida Zaid, Azerbaijan State Oil and Industry University PhD student, the Faculty of Chemical Engineering E-mail: Farida086@mail.ru Baghiyev Vagif Lachin, Azerbaijan State Oil and Industry University Professor, Department of chemistry and chemical materials engineering E-mail: Vagif_bagiev@yahoo.com
Influence of the crystallinity degree of cobalt-containing catalysts on their activity in the steam reforming reaction of ethanol into hydrogen
Abstract: In the paper were studied the degree of crystallinity and activity of cobalt-containing catalysts in the reaction of ethanol steam reforming into hydrogen. A comparison of the degree of crystallinity and activity of studied cobalt containing catalysts showed that with rising of crystallinity degree the rate of hydrogen production over Zn-Co-O and Fe-Co-O catalysts increases, while over Mg-Co-O decreases.
Keywords: ethanol, steam reforming, binary catalysts, cobalt oxide, crystallinity.
High activity in a steam reforming reaction of Experimental
ethanol is showing simple and complex catalysts Cobalt-containing catalysts of various compo-
based on cobalt oxide [1-3]. Previously we studied sitions were prepared by co-precipitation method
the effect of addition of magnesium, zinc and iron from aqueous solutions of nitrate salts of cobalt,
to cobalt oxide activity in steam reforming reac- magnesium, iron and zinc. The obtained mixture
tion of ethanol into hydrogen [4-6]. Studies have was evaporated and dried under 100-120 °C, de-
shown that the binary cobalt containing catalysts composed until complete separation of nitrogen
have high activity in a steam reforming reaction oxides at 250 °C, and then calcined at a temper-
of ethanol to hydrogen. The catalyst activity it is ature 550 °C during 10 hours. Thus, 27 catalysts
known in some way dependent on the structur- were prepared with the atomic ratio of elements
al properties of the catalyst. One of the catalyst from Me: Co = 1: 9 to Me: Co = 9: 1 (where Me is
properties, which is determined by the structural Mg, Zn or Fe).
properties of the solid compounds, is crystallinity, X-ray study of the phase composition of the pre-
which depends on the preparation conditions and pared catalysts were carried out by powder diffrac-
chemical composition of prepared catalyst. In this tometer «D2 Phaser» (CuKa-radiation, Ni-filter).
regard, the present work is devoted to studying The degree of crystallinity of the synthesized sam-
the effect of crystallinity binary cobalt-containing ples are calculated using "Diffrac.eva" program.
catalysts on their activity in the steam reforming Activity of catalysts were studied in the flow
reaction of ethanol to hydrogen. unit at a volumetric feed rate of 1200 h-1 in the
temperature range 200-700 °C. The quartz reactor was charged with 5 ml of the catalyst grained 1.0-2.0 mm and its activity was studied in a steam reforming reaction of ethanol. Outputs of hydrogen, methane and CO were determined on a gas chromatograph with 2m length column, filled with activated carbon. The yields of ethylene, acetaldehyde, and unreacted ethanol were determined on chromatograph with a flame ionization detector with 1 m length column, filled with sorbent polisorb-1.
Results and discussions
Carried out x-ray studies of binary systems Fe-Co-O, Zn-Co-O and Mg-Co-O showed that, in all three systems is observed formation of only two initial oxides phases, namely, Fe2O3 and Co3O4, ZnO and Co3O4, MgO and Co3O4. The calculated values of the crystallinity degree of binary cobalt-containing catalysts are given in Table 1.
The table shows that for the Mg-Co-O system the crystallinity of the samples increases with increasing magnesium content in their composition from 14.9% on the catalyst Mg: Co = 1:9 to 31.9% on the catalyst Mg: Co = 9:1. Practically similar dependences obtained for other systems. Thus, for Zn-Co-O system crystallinity of the samples increases with increasing zinc content in their composition from 14.7% for catalyst Zn: Co = 1: 9 to 68.5% for catalyst Zn: Co = 9: 1, and for Fe-Co-O catalytic system crystallinity of samples increases from 16.6%
for the catalyst Fe: Co = 1: 9 to 31.9% for the catalyst Fe: Co = 9: 1.
Table 1. — The crystallinity of the samples of Mg-Co-O, Zn-Co-O and Fe-Co-O catalytic systems.
Atomic ratio Me: Co Crystallinity,%
Mg-Co-O Zn-Co-O Fe-Co-O
1:9 14.9 14.7 16.6
2:8 14.7 18.1 21.2
3;7 15.9 16.6 16.7
4:6 16.3 18.3 17.4
5:5 17.9 21.4 23.3
6:4 15.4 23.0 28.4
7:3 17.8 31.1 26.2
8:2 19.2 40.5 36.7
9:1 31.9 68.5 37.5
As seen from the experimental data, there is a direct relationship between the catalyst composition and its degree of crystallinity. Crystallinity of binary solid oxide catalysts may effect on their catalytic activity.
Dependence of product outputs of steam reforming reaction of ethanol into hydrogen from the degree of crystallinity of Mg-Co-O catalysts are shown in Figure 1. It can be seen that the yields of hydrogen and carbon monoxide decrease with increasing of crystallinity degree of the samples, while methane yield increases. In this case for increasing the reaction rate ofhydrogen formation is necessary to reduce the degree of the catalyst crystallinity.
♦ H2 HCO A CH4
60
50
40
^ 30
o ?
20
10
10
15
20 25
Crystallinity, %
30
35
Fig.1. Dependencies of hydrogen, carbon monoxide and methane outputs from the crystallinity of Mg-Co-O catalytic system
Influence of the crystallinity degree of cobalt-containing catalysts on their activity.
Influence of the degree of crystallinity of the cobalt-zinc oxide catalysts for their activity in a steam reforming reaction of ethanol into hydrogen are shown in Figure 2. Figure 2 shows that for Zn-Co-O catalysts hydrogen yield increases with the rising of crystallinity degree of the catalyst and carbon monoxide and methane yields does not depend on the degree of crystallinity. Thus on the Zn-Co-O catalysts crystallinity of the catalyst plays a positive important role only in formation reaction ofhydrogen.
Figure 3 shows dependencies of the hydrogen, methane and carbon monoxide outputs in a steam reforming reaction to ethanol over iron-cobalt oxide catalysts from their degree of crystallinity. It can be seen that with increasing of crystallinity degree of the catalyst the yield of hydrogen increases, while outputs ofbyproducts, namely methane and carbon monoxide are virtually independent of the degree of crystallinity. This allows us to say that high value of crystallinity degree of the catalyst plays the positive role in order to obtain a high hydrogen yield.
Fig. 2. Dependencies of hydrogen, carbon monoxide and methane outputs from the crystallinity of Zn-Co-O catalytic system
Fig. 3. Dependencies of hydrogen, carbon monoxide and methane outputs from the crystallinity of Fe-Co-O catalytic system
Thus based on the obtained results it can be said hydrogen. This suggests us to say that the active centhat in the case of Fe-Co-O and Zn-Co-O catalytic ters responsible for the steam reforming reaction of systems rising of the crystallinity degree leads to in- ethanol over the catalysts Fe-Co-O and Zn-Co-O creasing of the hydrogen yield, but in the case of have a high degree of crystallinity, and for the Mg-Mg-Co-O catalysts leads to a decrease in yield of Co-O catalysts have a low degree of crystallinity.
References:
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Aliyeva Mahira Iosaf, Azerbaijan State Oil and Industry University PhD student, the Faculty of Chemical Engineering E-mail: bvl_ok@rambler.ru Baghiyev Vagif Lachin, Azerbaijan State Oil and Industry University Professor, Department of chemistry and chemical materials engineering
E-mail: Vagif_bagiev@yahoo.com
Activity dependence of the binary vanadium oxide catalysts from specific surface area
Abstract: In the paper were studied influence of the specific surface area of the vanadium containing catalysts on its activity in propylene oxidation reaction. It is found that increasing of surface area leads to decreasing of acetic acid yield over Sn-V-O catalysts but to increasing of acetic acid yield over Mo-V-O catalysts, while over W-V-O catalysts yields of acetic acid did not change.
Keywords: propylene, oxidation, binary catalysts, vanadium oxide, specific surface area.
Vanadium oxide is part of many catalysts for oxi- containing catalysts to their activity in a oxidation
dation of organic chemicals [1; 2]. Propylene is one of propylene. of the organic compounds, which could be oxidiz- Experimental
ing over catalyst systems based on vanadium oxide Vanadium-containing catalysts of different com-
[3; 4]. Metal oxides such as titanium, molybdenum, positions were prepared by co-precipitation from
tin, bismuth, et al. often used as additives to vana- aqueous solutions of salts of tin, molybdenum,
dium oxide [5-8]. Adding the second metal to va- tungsten and vanadium. The obtained mixture was
nadium oxide may vary surface properties including evaporated and dried under 100-120 °C, decom-
specific surface area, which can affect to its catalytic posed until complete decomposition of the initial
activities. Therefore, in this paper were studied the salts at 250 °C, and then calcined at temperature
effect of the specific surface area ofbinary vanadium 550 °C within10 hours. Thus, the 27 catalysts were
