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AZ9RBAYCAN KIMYA JURNALI № 1 2016
UOT 541.128
ELECTRON-ACCEPTOR CENTRES IN Fe-Zr/Al OXIDE CATALYSTS AND THEIR PARTICIPATION IN THE CONVERSION OF ETHANOL
INTO HYDROCARBONS
N.M.Aliyeva, E.E.Mammadov, F.i.Qasimova, L.Kh.Qasimova, E.H.ismailov,
Sh.F.Taghiyeva
Yu.Mamedaliyev Institute of Petrochemical Processes NAS of Azerbaijan
[email protected] Received 01.07.2015
Electron-acceptor (EA) and electron-donor (ED) centres in Zr/Al, Fe-Zr/Al oxide catalysts and their concentration as a function of composition of catalysts are determined using EPR spectroscopy of adserbed diphenylamine and nitrobenzene molecules. In situ EPR spectroscopy of catalysts in combination with on line chromatografic analysis of gas-phase products of the conversion of ethanol into hydrocarbons also was used. The rate of the yield of olefins as a function of the concentration of EA centres in catalysts was studied and it was established that the EA centers are the catalytically active centres of the conversion of ethanol into hydrocarbons on the aluminium oxide catalysts. The phase composition of Zr/Al, Fe-Zr/Al oxide catalysts and distribution of the catalytically active components on the surface of these catalysts were controlled using X-ray diffraction and X-ray fluorescence microscopy, accordingly.
Keywords: ethanol, hydrocarbons, aluminium oxide based catalysts, electron-acceptor centers.
Introduction
It was established that the aluminium oxide and they modified with different ions can be used as effective catalysts for conversion of alcohols into olefins. In spite of the intensive investigations in this direction during the last 2025 years the nature of catalytic active centers and the mechanism of these reactions are under the discussions [1-7].
The aim of this work is to study the EA and ED centers of Zr/Al, Fe-Zr/Al oxide contacts and their participation in the conversion of ethanol into hydrocarbons over these contacts.
Experimental part
The catalysts were prepared by wet impregnation technique of y-alumina support with the ZrOCl2-8H2O and FeCh^O solutions. The prepared samples of catalysts were dried at 393 K and then calcined in the presence of flow of purified air at 873 K for six hours [6]. These catalysts are tested in the conversion of ethanol to gasoline range hydrocarbons at 573 K and atmospheric pressure. The number of EA and ED centers in the samples is determined on the based on the analysis ESR spectra of adsorbed molecules of diphenylamine and nitro-
benzene, accordingly. The Jeol JES-PE-3X ESR spectrometer is used for the getting these spectra. This spectrometer in combination with LXM 80 (Russia) chromatograph and flowing micro-catalytic reactor is used also to determine the magnetic state of catalyst and composition of gas-phase products of the reaction of catalysts with ethanol at the temperature range 493-673K. Phase composition and microstructure of the powders are determined by X-ray diffraction method using XRD TD3500, China using CuKa-radiation. The average sizes of the granules FeOx/Al2O3, ZrO2/Al2O3, Fe-Zr/A^Os evaluated from the width of diffractograms based on Debye-Scherer formula: d=kX/pcos0, where d - the average size of crystallites, X - length of the radiation wave X(CuKa) = 1.54051 A, p -width of the peak on the half of height, 0 -diffraction angle, k = 0.9.
Results and discussions
The reaction products distribution of the conversion of ethanol over the tested catalysts sample is given in the table 1. As can be seen from the data in table 1 wiith the increasing the content of Zr in the samples the yield of the ethylene is increased til to 72% by mass. But at
АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 1 2016
the same time the studies show that at the first 40-50 min of this reaction the maximum of the yield of ethylene is reached and then the decrease of the formation of ethylene is decreased. The study of the yield of the reaction as a function of duration of the reaction at the temperature range 558-593 K shows the formation mainly of higher aliphatic (saturated and unsaturated) and aromatic hydrocarbons.
Table 1. Products of the conversion of ethanol into hydrocarbons over the aluminium oxide based catalysts at 578 K and atmospheric pressure
Yield, %
c o r <D O C s s
Catalyst ethylene saturated hydrocarbon S3 "o 2 C2 A aromatic hydrocarbon
1.0%Zr/Al2O3 100 62 15 13 10
3.0%Zr/Al2O3 100 72 5 16 7
0. 3 %Fe+1.0%Zr/Al2O3 100 65 18 12 5
1.0%Fe+1.0%Zr/Al2O3 100 58 21 10 11
In the table 2 the number of EA and ED centers and the rate of the ethylene yield as a function of the concentration of Cl- and SO4-ions in the samples is given.
Table 2. The number of EA and ED centers (N, spin/g) and the rate of yield of ethylen (w, mols-1g-1) as a functiom of the concentration of additives
1.0%Zr/Al203
Parameters The entered anion, mass. %
Cl- SO4-
- 1 2 4 2 4 8
The rate of the
yield of ethylene, w 108 5 7 8.8 9.5 13 15.5 25
Number of EA
centers, N4016 5 6.5 8.5 7 5 7.5 16
1.0%Fe+1.0%Zr/Al203
The entered anion, mass %
Cl- so4-
- 1 2 4 2 4 8
The rate of the
yield of ethylene, w 108 4 7.5 8 1.1 1.4 1.6 1.5
Number of ED,
N1016 2.8 2.3 2.0 2.0 2.0 1.7 0.6
sampls the rate of the formation of ethylene is increased. Consquently the EA centers can be discussed as the catalytic active centers for the conversion of the ethylene into ethylene.
It is welknown that the thermal decomposition of ethanol without catalyst is going hardly and not selective. The reaction goes at high temperatures (>973 K) and in two directions. When the ethyl alcohol passes through the quartz reactor filled with glass splinters and heated up to 973 K approximately 20% of ethanol converts into ethylene and water and 80% of the ethanol is converted into aldehyde (vinegar) and hydrogen. If the quartz reactor is filled in with aluminum oxide-based catalyst samples particles instead of glass splinters the conversion of ethylene takes place at 573 K and with 70-80% selectivity on ethylene and acetaldehyde is not form. Until today the reaction mechanism is discussed. Reaction mechanism is still subject to debate, the infor-maion about the reaction active centers, intermediate compounds is very pour and different. In addition, it should be noted, in homogeneous environment in the presence of sulfuric acid reaction is going at 443 K with the formation of ethylene and water. As a catalytic species in this reaction the hydrogen ions obtained by dis-sosiation, for example, of sulfuric acid participate.
In the table 3 the number of EC and ED centers in the samples as the function of their calcination temperature in air is given.
Table 3. The number of EA centers as a function of
Number of EA and ED centers, 1016spin/g The calcination temperature, K
473 673 873 1073
EA 5 17 32 38
ED 3 12 29 34
As can be seen from this table with the increasing the number of the EA centres in the
From the EPR spectra of adsorbed diphe-nylamin it was shown that the number of EA centers in the samples increase with the increasing the temperature of their calcination in air. The EPR spectra of the samples with adsorbed diphenylamine and nitrobenzene recorded at room temperature are given in Fig.1 and 2.
At the Figure 3 and 4 the X-ray fluorescent spectrum and X-ray diffractograms of modified aluminium oxide catalysts are given.
N.M.ALIYEVA et al. Cation radical of diphenylamine
+
NH
а
b
Figure 1, a-c. EPR spectra recorded at room temperature of the calcined in air at 873 K Zr/Al oxide sample with adsorbed diphenylamine 873 K after: a - 0.5, b - 4 hours and c - 2 days.
Anion-radical of nitrobenzene
c
Figure 2. EPR spectra recorded at room temperature of the calcined in air at 873 K Zr/Al oxide sample with adsorbed nitrobenzene diphenylamine 873 K after 0.5 hour.
Fe Ir 1 Spectrum 13
h Zr
Ш 1 I
0 5 10 15 20 25 30 35 40
Full Scale 6988 cts Cursor: 0.227 (58 cts) keV
Figure 3. X-ray fluorescent spectrum of 5%Fe+5%Zr/Al2O3 sample. АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 1 2016
150
100
50
1 ill \
I , J* Fl , JlíLMT г 4 Vl I 1 У
Tlieta ((leg)
a
b
Figure 4. X-ray difractograms of 3% Zr/Al2O3 samples calcined in air at: a - 873 K and b - 1073 K.
Conclusion
Thus the investigations which carried out show the following.
1. It was shown that the gas-phase products of the conversion of ethanol over Zr/Al oxide sample which contain only 1.0 wt.% Zr consist of mainly from ethylene (~62%). The dependance of the reaction products yield on the reaction duration shows the formation of mainly etnylene at the first 40-50 minuts in the temperature range 558-593 K and then the formation of the hiigher saturated and unsaturated alifatic and aromatic hydrocarbons.
X-ray fluorescence microscopy shows that the channging in the yield of etylene depending on the duration of the reaction is due to changinng the surface structure and elemennt composition of catalysts. It was shown that the dependance between the formation rate of olefins and the concentration of EA centers in the catalysts are linear.
2. The concentration of the EA and ED centers EPR is determined using EPR spectroscopy of adsorbed diphenylamine and nitrobenzene, accordingly. It was shown that the introduction of the Cl- and SO2- anions leads to
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N.M.ALIYEVA et al.
concentration of EA centers and the rate of the formation of ethylene.
3. The carried out investigations alow to consider the EA centers as the catalytic active centers for conversion of ethanol into hydrocarbons over the aluminium based oxide catalysts and at the second to develop the tecnology fo preparation of the active in the conversion of ethanol into hydrocarbons by modification of aluminium oxide with zirconium cations and anions such as Cl- and SO 2-.
References
1. Narayanan C.R., Srinivasan S., Datye A.K., et al. The effect of alumina structure on surface sites for alcohol dehydration // J. Catal. 1992. V. 138. P. 659-674.
2. Golay S., Doepper R., Renken A. Insitu characterization of the surface intermediates for the ethanol dehydration reaction over y-alumina under dyna-
mic conditions // Appl. Catal., A: General. 1998. V. 172. P. 97-106.
3. Zaki T. Catal. dehydration of ethanol using transition metal oxide catalysts // J. Colloid Interface Sci. 2005. V. 284. P. 606-613.
4. Makgoba N.P., Sakuneka T.M., Koortzen J.G. et al. Silication of y-alumina catalyst during the dehydration of linear primary alcohols // Appl. Catal., A: General. 2006. V. 297. P. 145-150.
5. Doheim M.M., Hanafy S.A. El-Shobaky G.A. Catalytic conversion of ethanol and isopropanol over the Mn2O3/Al2O3 system doped with Na2O // Mater. lett. 2002. V. 55. No 5. P. 304-311.
6. Doheim M.M., El-Shobaky H.G. Catalytic conversion of ethanol and iso-propanol over ZnO-treated Co3O4/Al2O3 solids // Colloids Surf., A: Physicochemical and Engineering Aspects. 2002. V. 204. P. 169-174.
7. Zhang X., Wang R., Yang X., Zhang F. Comparison of four catalysts in the catalytic dehydration of ethanol to ethylene // Microporous Mesoporous Mater. 2008. V. 116. P. 210-215.
Zr/Al, Fe-Zr/Al OKSiD TORKiBLi KATALiZATORLARDA ELEKTRON-AKSEPTOR MORKOZLORi УЭ ETANOLUN KARBOHiDROGENLORO CEVRiLMOSi REAKSiYASINDA
ONLARIN ROLU
N.M.Oliyeva, E.E.Mammadov, F.i.Hüseynova, L.X.Qasimova, E.H.ismayilov, §.F.Tagiyeva
Zr/Al, Fe-Zr/Al oksid katalizatorlann elektron-akseptor (EA), elektron-donor (ED) markazlari, etanolun karbohidrogenlara konversiyasi reaksiyasinda bu markazlarin katalitik aktiv markaz kimi rolu tadqiq olunmu§dur. Katalizatorlarin faza tarkibi rentgen difraksiyasi, sathda aktiv elementlarin paylanma manzarasi rentgenofluoressent mikroskopiyasi, maqnit xassalari electron maqnit rezonansi spektroskopiyasi va reaksiyanin qaz fazasinin tarkibi qaz xromatoqrafiyasi metodlari ila öyranilmi§dir. Olefinlarin alinma süratinin elektron-akseptor (EA) markazlarinin sayindan asililigi dinamikasi tadqiq edilmi§ va elektron-akseptor tabiatli markazlarin etanolun karbohidrogenlara konversiyasi reaksiyasinin aktiv markazlari oldugu müayyan edilmi§dir.
Agar sözlzr: etanol, karbohidrogenlar, alüminium oksid asasli katalizatirlar, elektron-akseptor markazlar.
ЭЛЕКТРОНО-АКЦЕПТОРНЫЕ ЦЕНТРЫ В Zr/Al, Fe-Zr/Al-ОКСИДНЫХ КАТАЛИЗАТОРАХ И ИХ РОЛЬ В КОНВЕРСИИ ЭТАНОЛА В УГЛЕВОДОРОДЫ
Н.М.Алиева, Э.Э.Маммадов, Ф.И.Гусейнова, Л.Х.Гасымова, Э.Г.Исмаилов, Ш.Ф.Тагиева
Исследованы электроно-акцепторные (ЭА) и электроно-донорные (ЭД) центры в Zr/Al Fe-Zr/Al-оксидных катализаторах и их роль в конверсии этанола в углеводороды. Исследованы также фазовый состав, распределение активных элементов на поверхности и приповерхностных слоях катализатора, магнитные свойства и распределение газофазных продуктов реакции методами рентгеновской дифрактометрии, рентгено-флуоресцентной микроскопии, электронного магнитного резонанса и газовой хроматографии соответственно. Получена зависимость скорости конверсии этанола от содержания в образцах ЭА центров и показано, ЭА центры являются каталитически активными в исследуемой реакции.
Ключевые слова: этанол, углеводороды, алюминий-оксидные катализаторы, электронно-акцепторные центры.
АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 1 2016
