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13CHEMICAL SCIENCES
THE DEPENDENCE OF Ti-W-O CATALYSTS ACTIVITY IN THE ETHANOL CONVERSION REACTION ON THE DEGREE OF CRYSTALLINITY
Aghayeva K.
PhD Student, Chemical technology faculty, Azerbaijan State Oil and Industry University, Baku, Azerbaijan
Ahmadova I.
Assistant professor, Chemical technology faculty, Azerbaijan State Oil and Industry University, Baku, Azerbaijan
Baghiyev V.
Doctor of chemical science, Professor, Chemical technology faculty, Azerbaijan State Oil and Industry University, Baku, Azerbaijan
Abstract
The reaction of ethanol conversion over binary titanium-tungsten oxide catalysts was studied. It was found that the conversion of ethanol over the studied catalysts begins at 150°C temperature with formation of acetalde-hyde, diethyl ether and ethylene. It has been established that over binary titanium-tungsten oxide catalysts with increasing degree of crystallinity, the yield of diethyl ether increases, while the yields of by-products decrease.
Keywords: Ethanol, Diethyl ether, Titanium oxide, Binary catalysts, Crystallinity.
Introduction
We have previously shown that ethanol is converted over titanium-tungsten oxide catalysts with high speed [1]. As it was established, the yield of reaction products was highly dependent on the composition of the catalyst. As is known, one of the properties of solid catalysts that affect to its activity is the crystallinity of a solid sample [2,3]. Therefore, in this work, we studied the effect of the degree of crystallinity of titanium-tungsten oxide catalysts on their activity in the reaction of ethanol conversion.
Experimentals
The synthesis of binary titanium-tungsten oxide catalysts of various compositions was carried out by co-precipitation from aqueous solutions of salts of titanium chloride and nickel nitrate. The resulting mixture was successively evaporated and dried at 100-120°C, decomposed until complete decomposition of the initial salts at 250°C, and then calcined at a temperature of 550°C for 10 hours. Thus, 9 catalysts were synthesized with an atomic ratio of elements from Ti:W=1:9 to Ti:W=9:1. The activity of the synthesized catalysts was studied on a flow-through installation with a quartz reactor in the temperature range of 150-500°C. 5 ml of the studied catalyst with a grain size of 1.0-2.0 mm
The degree of crystallinity of binary titanium-
were loaded into the reactor, and its activity in the eth-anol conversion reaction was studied. The yields of the ethanol conversion products, as well as the ethanol conversion, were determined on an chromatograph with a flame ionization detector with a 3 m long column filled with specially treated Polysorb-1 sorbent. The amount of formed carbon dioxide was determined on a chromatograph with a 6m column filled with an Celite sorbent coated with liquid paraffin. X-ray studies of binary titanium-tungsten oxide catalysts were carried out on a Bruker automatic powder diffractometer D2 Phaser (CuKa radiation, Ni filter, 3<29>80 °).
Results and discussion
The results of X-ray diffraction studies showed that two phases of anatase and rutile titanium oxide and a tungsten oxide phase are formed in the Ti-W-O catalyst system. The analysis of X-ray diffraction patterns showed that the samples rich in tungsten consist of phases of titanium oxide (anatase) and tungsten oxide. In titanium rich samples, the formation of a rutile titanium oxide phase is also observed. In all samples, the percentage ratio of the components is preserved, as evidenced by the regular change in the intensities of reflections in diffraction patterns. The crystallinity degrees of the studied samples were also calculated, which are shown in table 1.
Table 1
The atomic ratio of titanium to tungsten 1-9 2-8 3-7 4-6 5-5 6-4 7-3 8-2 9-1
Degree of crystallinity, % 83.4 82.1 83.8 77.2 78.1 75.7 71.9 70.7 70.2
As can be seen from table 1, the degree of crystallinity of the Ti-W-O catalyst system with an increase of the titanium content in the catalyst composition decreases from 83.4% in the sample Ti-W=1-9 to 70.2% in the sample Ti-W=9-1.
The study of the activity of the studied samples showed that the reaction products of the conversion of
ethanol over Ti-W-O catalyst system are diethyl ether, acetic aldehyde and ethylene. Table 2 shows the dependence of the yields of the reaction products of ethanol vapor conversion on the atomic ratio of titanium to tungsten in the composition of Ti-W-O catalysts.
Table 2.
The dependence of the yields of the reaction products of the conversion of ethanol on the atomic ratio _of titanium to tungsten in the composition of the catalyst._
Reaction products Yields
The ratio of titanium to tungsten 1-9 2-8 3-7 4-6 5:5 6-4 7-3 8-2 9-1
Ethylene 4,6 2,9 7,1 11,7 17,3 21,9 37,8 29,4 41,8
Acetic Aldehyde 11,5 10,9 9,6 10,9 15,4 15,4 8,3 19,2 9,8
Diethyl ether 24,5 34,1 49,8 46 34,9 27,7 0 0 0
Ethanol conversion 40,6 47,9 66,5 68,6 67,6 65,1 46,4 48,7 51,6
It can be seen that with an increase in the titanium content in the catalyst, the yield of diethyl ether increases and reaches 49.8% on the sample Ti-W=3:7 catalyst and then begins to decrease and on the Ti-W=7:3 sample it is already equal zero. The yield of ethylene, as can be seen from Table 2, increases with increasing titanium oxide content in the binary titanium-tungsten oxide catalyst. So, the ethylene yield on the Ti-W=1:9 sample is equal 4.6%, while on the Ti-W = 9: 1 sample it is already equal 41.8%. From table 2 it is also seen that the yield of acetic aldehyde passes through a maximum on the catalyst Ti-W=8:2 sample, which is 19.2%. The ethanol conversion also passes
through a maximum with a change in the titanium content in the binary titanium-tungsten oxide catalyst and does not exceed 68.6%.
Figure 1 shows the dependence of the yields of the reaction products of ethanol conversion on the crystal-linity of binary titanium-tungsten oxide catalysts. Figure 1 shows that with increasing degree of crystallinity of the catalyst, the yield of diethyl ether increases, while the yield of ethylene decreases. Figure 1 also shows that the yield of acetic aldehyde also decreases with increasing degree of crystallinity of the catalyst, but to a small extent.
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Fig. 1 The dependence of the yields of the reaction products of ethanol conversion on the degree of crystallinity
of binary titanium-tungsten oxide catalysts.
Conclusion
Based on the conducted studies, it can be said that an increase in the degree of crystallinity of binary titanium-tungsten oxide catalysts accelerates the formation of diethyl ether and reduces the yields of reaction byproducts, namely ethylene and acetic aldehyde.
REFERENCES:
1. Aghayeva K.X., Baghiyev V.L. Ethanol Conversion over Binary Ti-W-O Catalysts. 5th International School-Conference on Catalysis for Young Scientists, Catalyst Design: From Molecular to Industrial Level, May 20-23, 2018, Moscow, Russia, ABSTRACTS, Novosibirsk, PP-V-22, p.279
2. Norman S.Allen, Noredine Mahdjoub, Vladi-mirVishnyakov, Peter J.Kelly, Roelof J.Kriek. The effect of crystalline phase (anatase, brookite and rutile) and size on the photocatalytic activity of calcined polymorphic titanium dioxide (TiO2), Polymer Degradation and Stability, Volume 150, April 2018, Pages 3136
3. Gihoon Lee, Ilho Kim, Inchan Yang, Jeong-Myeong Ha, Hyon Bin Na, Ji Chul Jung. Effects of the preparation method on the crystallinity and catalytic activity of LaAlO3 perovskites for oxidative coupling of methane. Applied Surface Science, Volume 429, 31 January 2018, Pages 55-61
