Dutov, Valeriy V.

Mamontov, Grigory V.

Sobolev, Vladimir I. (химик)

Vodiankina, Olga V.

English

Tomsk State University Repository

Boreskov Institute of Catalysis SB RAS, Novosibirsk Zelinsky Institute of Organic Chemistry RAS, Moscow Lomonosov Moscow State University, Moscow Arbuzov Institute of Organic and Physical Chemistry KSC RAS, Kazan XII European Congress on Catalysis  ”Catalysis: Balancing the use of fossil and renewable resources” Kazan (Russia) 30th August - 4th September, 2015 Novosibirsk - 2015ABSTRACTS12th European Congress on Catalysis – EuropaCat-XII, Kazan, Russia, 30 August – 4 September, 2015  2111ISO-PP06 Silica-Supported Silver-Containing OMS-2 Catalysts for Ethanol Oxidative Dehydrogenation Dutov V.1*, Mamontov G.1, Sobolev V.1,2, Vodyankina O.1 1 - Tomsk State University, Tomsk, Russia 2 - Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia * dutov_valeriy@mail.ru Keywords: selective oxidation, ethanol, manganese, octahedral, molecular, sieve, silver, silica 1 Introduction High activity of supported silver catalysts in selective oxidation of alcohols was shown in many studies [1, 2]. Catalytic activity of Ag-containing catalysts, in particular, Ag/SiO2, may be increased by addition of transition metal oxides [3]. Manganese oxides are expected to be suitable modifiers for Ag/SiO2 catalyst due to reversible Mn4+/Mn3+ redox cycle. It is known that silver-containing cryptomelane-type manganese dioxide catalysts (Ag/OMS-2) have high activity and selectivity in oxidation of alcohols, in particular, octanol-1 and ethanol [4, 5]. However, oxidation of ethanol over OMS-2 catalysts is carried out using gas mixture containing low concentration of oxygen, generally 1-10 vol. % [5, 6] because of high activity of these catalysts in deep oxidation. One of the ways to control the redox, catalytic and acid-base properties of metal oxides is the use of different supports. The purpose of present research work is to design the method to prepare highly effective Ag/OMS-2/SiO2 catalysts and investigate their catalytic properties in oxidative dehydrogenation of ethanol. 2 Experimental  To prepare Ag/OMS-2 catalysts two different methods were used. At first, OMS-2 sample was prepared by procedure described in [7], and then it was impregnated with water solution of AgNO3 followed by calcination in air flow at 500 оС (Ag/OMS-2-I). In the co-precipitation method (CP) AgNO3 was added in course of preparation of OMS-2. Nominal amount of Ag was 5 % wt. The Ag/OMS-2/SiO2 catalysts were prepared by the sequential impregnation (SI) and co-precipitation (CP) methods. In the first method silica was impregnated with appropriate quantity of KMnO4 solution and then dried at 60 oC. The obtained KMnO4/SiO2 sample was added into the acidified water solution of Mn(NO3)2 under stirring. After that the obtained mixture was heated in autoclave for 24 h, then the precipitate was filtered, washed and dried. The obtained OMS-2/SiO2 sample was impregnated with water solution of AgNO3 followed by calcination in air flow at 500 оС. According to the second method, KMnO4/SiO2 was added into the mixed solution of Mn(NO3)2 and AgNO3. The catalysts were characterized by TPR-H2, TPO, TPSR-C2H5OH, XRD, TEM, AES and N2 adsorption at -196 oC. Catalytic activity of the samples in ethanol oxidation was tested in a flow fixed-bed reactor at atmospheric pressure using 0.5 g of catalyst. Gas mixture containing 2 %vol. C2H5OH and 18 vol. % O2 in He was passed through reactor at total flow rate of 60 cm3/min. The effluents from the reactor were analyzed by on-line gas chromatography. Prior to catalytic experiment the catalysts were treated in 8 % O2/He at 500 oC for 1 h.  3 Results and discussion  Investigation of chemical composition of the prepared catalysts revealed that using of co-precipitation method (CP) resulted in partial loss of Ag due to leaching of silver in course of hydrothermal treatment.  12th European Congress on Catalysis – EuropaCat-XII, Kazan, Russia, 30 August – 4 September, 2015  2112The OMS-2, Ag/OMS-2-I and Ag/OMS-2-CP catalysts were used as model systems for detailed characterization of supported catalysts. To investigate the effect of silver addition on the active sites of OMS-2 TPSR of adsorbed ethyl alcohol were carried out. Formation of water was observed for all catalysts at 80 oC in course of ethanol adsorption in pulse mode, therefore adsorption and dehydration of ethanol occursed on the acid sites. The quantity of adsorbed alcohol was 221, 172 and 142 µmol/g for OMS-2, Ag/OMS-2-CP and Ag/OMS-2-I catalysts, respectively. Carbon dioxide was the main product of TPSR and released at 170 and 230 oC.  Investigation of catalytic activity of prepared OMS-2/SiO2, Ag/OMS-2/SiO2-SI and Ag/OMS-2/SiO2-CP catalysts in oxidative dehydrogenation revealed that addition of silver results in increasing of the ethanol conversion. This may be explained by increasing of reaction ability of surface oxygen in the presence of silver, which was confirmed by TPR-H2. The effect of silver content and Mn/Ag molar ratio on the catalytic properties was investigated. It was stated that silver content insignificantly effect on the ethanol conversion. However, selectivity towards acetaldehyde depends on silver content. For Ag/OMS-2/SiO2-CP catalyst the selectivity towards acetaldehyde at temperatures above 200 oC is lower in comparison with the one for Ag/OMS-2/SiO2-SI due to low silver content (higher molar ratio Mn/Ag) or formation of mixed Ag-Mn phase in course of synthesis via co-precipitation.   Fig. 1. Catalytic properties of OMS-2/SiO2, Ag/OMS-2/SiO2-SI and Ag/OMS-2/SiO2-CP Generally, deep oxidation activity of Ag-containing supported catalysts is higher than the one for OMS-2/SiO2, which may be associated with increasing of reoxidation ability in presence of silver (according to TPO data). 4 Conclusions  The Ag/OMS-2/SiO2 and OMS-2/SiO2 catalysts were synthesized and tested in ethanol oxidation. It was stated that silver addition increases the reducibility and reoxidation ability of OMS-2, as a consequence catalytic activity increases. Catalytic properties of Ag/OMS-2/SiO2 catalysts may be controlled by variation of Mn/Ag molar ratio and preparation method.  Acknowledgements  This work was supported by the RFBR (project mol_NR 14-33-50483) References1  L. Ma, L. Jia, X. Guo, L. Xiang, Chinese Journal of Catalysis. 35 (2013) 108. [2]  O. Vodyankina, A. Blokhina, I. Kurzina, V. Sobolev, K. Koltunov, Catalysis Today. 203 (2013) 137.  [3]  T. Kharlamova, G. Mamontov et al., Appl. Catal. A: General. 467 (2013) 519. [4]  G. D. Yadav, R. K. Mewada, Chemical Engeneering Research and Design. 90 (2012) 86.  [5]  J. Chen, J. Li et al., Chinese Journal of Catalysis. 28 (2007) 1034. [6]  H. Zhou, J. Y. Wang et al., Microporous and mesoporous materials. 21 (1998) 315. [7]  R. N. DeGuzman, Y-F. Shen, E. J. Neth, S. L. Suib et al., Chem. Mater. 6 (1994) 815.  

Silica-supported silver-containing OMS-2 catalysts for ethanol oxidative dehydrogenation

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Silica-supported silver-containing OMS-2 catalysts for ethanol oxidative dehydrogenation

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