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37Thus 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:
1. Simonetta Tuti, Franco Pepe, Catalysis Letter (2008), 122, P. 196-203.
2. FumihiroHaga, Tsuyoshi Nakajima, Hidemaru Miya and Shozi Mishima, Catalysis Letters, 48, (1997), P. 223-227.
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Aliyeva Mahira Iosaf, Azerbaijan State Oil and Industry University PhD student, the Faculty of Chemical Engineering E-mail: [email protected] Baghiyev Vagif Lachin, Azerbaijan State Oil and Industry University Professor, Department of chemistry and chemical materials engineering
E-mail: [email protected]
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
synthesized the elements of atomic ratio from Me: V = 1: 9 to Me: V = 9: 1 (where Me is Sn, Mo and W).
The specific surface area of the synthesized samples was determined by thermal desorption of nitrogen.
Activity of synthesized catalysts were studied in the flow unit at a volume 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 1.02.0 mm and its activity was studied in a propylene oxidation reaction. Outputs of carbon dioxide and propylene determined by chromatograph with a column length 3m. packed with polysorb-1 coated by Vaseline oil. Acetaldehyde, acetic acid and acetone yields were determined on chromatograph with a flame ionization detector on a column 2 m in length, filled with sorbent polisorb-1.
Results and discussion
The measurement of the surface area of the individual oxides showed that the specific surface areas of vanadium oxide, tin oxide, molybdenum oxide and tungsten oxide are respectively 8.2 m2/g, 3.3 m2/g, 1.9 m2/g and 6.6 m2/g.
Summarizes results of study of the specific surface area of Sn-V-O, Mo-V-O, and W-V-O catalysts by thermal desorption of nitrogen are showed in table 1. As seen from the table for the tin-vanadium oxide catalysts with increasing content of tin in the catalyst surface area remains virtually unchanged till the sample composition Sn: V=6:4 then rises sharply to 35 m2/g over sample composition Sn: V=8:2 and then reduced to 10.3 m2/g at the sample composition Sn: V=9:1.
Unlike previous catalyst system, the specific surface area of molybdenum-vanadium oxide catalysts increases slightly with increasing molybdenum content in the catalyst. In this catalytic system, the maximum specific surface area is also observed on the sample with the ratio of Mo: V=8:2. In this sample, the specific surface area is 3.7 m2/g.
As seen from the table 1 for tungsten-vanadium oxide catalysts is observed dependence of the specific surface area from the tungsten content with two maxima. The first peak is observed on the catalyst W: V=2:8 (4.2 m2/g), and the second on the catalyst
W: V=7:3 (6.1 m2/g). Table 1 also shows that the specific surface area for tungsten-vanadium oxide catalysts varies from 2.2 m2/g on the catalyst W: V = 9: 1 to 6.1 m2/g on the catalyst W: V = 7: 3.
Thus summarizing the above one we can say that the value of specific surface area of binary vanadium containing catalysts are reduced in the following sequence:
Sn-V-O > W-V-O > Mo-V-O
Table 1. - Specific surface area of binary vanadium containing catalysts
Catalyst composition Catalytic system
Sn-V-O Mo-V-O W-V-O
1-9 1.4 1.2 3.9
2-8 11 1.3 4.2
3-7 10.1 1.5 3.6
4-6 10.5 2.1 2.8
5-5 10.4 2.7 4
6-4 11.3 2 3.5
7-3 13.4 3.2 6.1
8-2 35 3.7 3.5
9-1 10.3 2.5 2.2
The surface porosity ofthe catalyst is an important factor affecting the catalytic activity of the samples. Figure 1 shows dependencies of product outputs of propylene oxidation reaction on the specific surface area of Sn-V-O catalysts. As it can be seen from Figure 1 for the Sn-V-O catalysts with increasing specific surface area value of propylene conversion and acetic acid yield is reduced while the carbon dioxide output slightly increases.
Depending of product outputs of propylene oxidation reaction from the specific surface area of Mo-V-O catalysts are given in Figure 2. As can be seen from figure 2 in contrast to the previous series of catalysts for Mo-V-O samples increases of the specific surface area of catalysts leads to increasing of propylene conversion and acetic acid yield, but the carbon dioxide yield is practically unchanged.
Effect of specific surface area of W-V-O catalysts to the product yields of propylene oxidation reaction are shown in Figure 3. It can be seen that the specific surface area ofW-V-O catalysts practically no effect on the conversion of propylene or the outputs of acetic acid and carbon dioxide.
Fig. 1. Dependencies of acetic acid, carbon dioxide outputs and propylene conversion from the specific surface area of Sn-V-O catalytic system
Fig. 2. Dependencies of acetic acid, carbon dioxide outputs and propylene conversion from the specific surface area of Mo-V-O catalytic system
Fig. 3. Dependencies of acetic acid, carbon dioxide outputs and propylene conversion from the specific surface area of W-V-O catalytic system
Based on the above obtained results we can say while for Mo-V-O catalysts promotes the conver-
that the surface area of binary vanadium containing sion of propylene and the yield of acetic acid. For
catalysts differently effect on the propylene oxida- W-V-O catalysts of the change in the surface area
tion reaction. In the case of Sn-V-O catalysts in- practically does not have any influence on both
creasing of the surface area leads to a reduction of propylene conversion and the yields of acetic acid
propylene conversion and the yield of acetic acid, and carbon dioxide.
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