Catal. Sustain. Energy 2017; 4: 59–61
Rapid Communication G.G. Volkova, V.A. Paukshtis
Carbonylation of Dimethyl Ether on Ag/ Cs1.5H1.5PW12O40: In-Situ FTIR Spectroscopy Study of the Ag-Carbonyls https://doi.org/10.1515/cse-2017-0009 Received November 23, 2017; accepted December 6, 2017
Abstract: Halide-free carbonylation of dimethyl ether (DME) to methyl acetate over heterogeneous catalysts offers a potentially green route to the production of important industrial chemicals. Previously we have shown that the addition of 1% of silver to Cs1.5H1.5PW12O40 led to an increase in activity by a factor of two. Formation of silver carbonyl clusters on the surface of the catalyst was demonstrated by in situ FTIR spectroscopy. The v(CO) of silver carbonyl was observed at 2188 cm-1 and may be explained by the formation of cationic silver carbonyl Ag(CO)+ on the surface of the acidic cesium salt of 12-tungstophosphoric acid. In view of the increased efficiency, the novel bifunctional catalyst Ag/ Cs1.5H1.5PW12O40 is expected to hold significant promise for practical use in new processes of basic organic chemistry. Keywords: carbonylation, dimethyl ether, acidic cesium salt of 12-tungstophosphoric acid, in situ FTIR spectroscopy, silver carbonyl
1 Introduction Acetic acid is an industrial chemical which is manufactured on a large scale. The main route to acetic acid is through the carbonylation of methanol which uses a homogeneous rhodium or iridium catalyst and a halide promoter [1]. The main disadvantages of this process are: a) halides are highly corrosive and are poisons for many types of catalysts, b) it is difficult to separate the products from
*Corresponding author: G.G. Volkova, Boreskov Institute of Catalysis, pr.Akademika Lavrentieva, 5, 630090, Novosibirsk, Russia, E-mail:
[email protected] E.A. Paukshtis, Boreskov Institute of Catalysis, pr.Akademika Lavrentieva, 5, 630090, Novosibirsk, Russia
the catalyst. Moreover, iodide cocatalysts are carcinogens and they should be avoided in “green” chemistry. These problems may be overcome by developing a heterogeneous catalyst that can operate effectively without a halide promoter. Dimethyl ether (DME) is more favorable for carbonylation than methanol because it can be produced from syn-gas more effectively [2]. CH3-O-CH3 + CO ® CH3-CO-O-CH3 Two types of acid catalysts are capable of activating C-O bonds in methanol or in DME: zeolites and heteropolycompounds. Starting with Cu mordenite [3] BP Chemicals Limited continued their discoveries in halide-free DME carbonylation with other acidic zeolites – H-ZSM5, and H-FER [4]. Wegman was the first to demonstrate that rhodium or iridium salts of tungstophosphoric heteropoly acid supported on silica can catalyze DME carbonylation to methyl acetate [5]. We subsequently have shown that acidic cesium salts of 12-tungstophosphoric acid promoted with rhodium can lead to a 10-fold enhancement in the activity of halide-free DME carbonylation to methyl acetate [6]. Recently we have observed that the addition of 1% of silver to Cs1.5H1.5PW12O40 led to an increase in activity by 100% [7], while Souma et al. have demonstrated the acceleration of carbonylation of alcohols and alkanes by 5-25% in the presence of Ag/ Nafion, Ag/ZSM-5, and Ag/SO4/ZrO2 [8]. Here we report the characterization of silver carbonyl clusters on the surface of the acidic cesium salt of 12-tungstophosphoric acid using in situ FTIR spectroscopy.
2 Experimental 2.1 Catalyst preparation The samples of Cs1.5H1.5PW12O40 catalysts 1) unpromoted and 2) promoted with silver were prepared by the
Open Access. © 2017 G.G. Volkova, V.A. Paukshtis, published by De Gruyter Open. Attribution-NonCommercial-NoDerivs 4.0 License.
This work is licensed under the Creative Commons
Unauthenticated Download Date | 1/24/18 1:43 AM
60
G.G. Volkova, V.A. Paukshtis
dropwise addition of a 0.1 M aqueous solution of cesium nitrate to the mixture of 0.1 M solutions of H3РW12O40 and silver nitrate taking into account the required ratio. The resulting suspension after vigorous stirring for 24 hours was evaporated at 100oC to leave the solid. The Cs1.5H1.5PW12O40 composition of the acidic cesium salt was chosen as the most active among other CsxH3-xPW12O40 catalysts [6].
2.2 In situ FTIR spectroscopy characterization FTIR spectroscopy in a thermostatted in situ IR cell was applied to determine the formation of carbonyls on the surface of the Ag/Cs1.5H1.5PW12O40 and Cs1.5H1.5PW12O40 catalysts by monitoring the adsorption of CO [9]. The samples were pressed into self supporting wafers containing 30 mg/cm2 of material and 50% of BaF2. Samples were reduced by hydrogen in the IR cell at 200oC for 60 min. and then treated with CO (250 torr) at 200oC for 60 min. All the spectra were recorded at 200oC in a CO atmosphere in the range of 400-6000 cm-1 with 4 cm-1 resolution, using a Shimadzu FTIR-8300 spectrometer.
CO, the v(CO) of silver carbonyl on Nafion was observed at 2173 cm-1 [8]. The band at 2188 cm-1 registered for the 1%Ag/Cs1.5H1.5PW12O40 catalyst can therefore be assigned to the formation of cationic silver carbonyl Ag(CO)+ on the surface of the acidic cesium salt of 12-tungstophosphoric acid. It is known that solid heteropolyacids and their salts can exhibit pseudoliquid phase behavior, so the rate of so called “bulk-type” reaction may be more than 100 times higher than the rate of “surface-type” reaction [11]. We can assume that the close value of v(CO) at 2186 to 2188 cm-1 for Ag(CO)+ in H2SO4 and on the surface of Cs1.5H1.5PW12O40 is connected with the pseudoliquid phase behavior of the acidic cesium salt of 12-tungstophosphoric acid.
3 Results and discussion The FTIR spectra of adsorbed CO on unpromoted acidic cesium salts of H3PW12O40 (Fig. 1, curve 1) revealed a very week band at 2170cm-1. This band can be attributed to CO adsorption on the surface of the Cs1.5H1.5PW12O40 catalyst. Ponec et al. assigned the band at 2167 cm-1 to CO adsorbed on 1% Na/WO3/Al2O3 catalysts. For pure WO3/Al2O3 sample the CO stretching band was found at 2193 cm-1[10]. Authors of this paper explained the difference in IR bands (2193 and 2167 cm-1) by various sites of CO adsorption. The band at 2193 cm-1 they assigned to CO adsorption on W+6 in WO3/ Al2O3 catalyst and the band at 2167 cm-1 to CO adsorbed in the neighbourhood of Na+ ions or on them in 1% Na/ WO3/Al2O3 catalysts. In our case we can suggest that CO adsorption occurs on the Cs+ ions in Cs1.5H1.5PW12O40 catalyst. The low intensity of the band 2170 cm-1 indicates that only trace amount of CO can be adsorbed on the surface of the Cs1.5H1.5PW12O40 sample. Adsorption of carbon monoxide on 1%Ag/ Cs1.5H1.5PW12O40 prereduced at 200oC results in the appearance of one band at 2188 cm-1 with high intensity (Fig.1, curve 2). Souma et al. have observed the v(CO) in the IR spectra at 2186 cm-1 for Ag(CO)+ in H2SO4 liquid media. When the solid catalyst Ag/Nafion was exposed to
Fig. 1. FTIR spectra of CO adsorption on Cs1.5H1.5PW12O40(1) and on Ag/ Cs1.5H1.5PW12O40 (2) after 60 min reduction in H2 at 200oC and admission of 250 torr CO at 200oC.
Previously, for rhodium promoted CsxH3-xPW12O40 catalysts, we have shown that 1) activation of the C-O bond in the DME molecule and formation of a metal-alkyl bond occurs in the presence of strong Bronsted acid sites and 2) these acid sites act in conjunction with Rh carbonyl complexes, which are responsible for CO insertion and acetate formation [12]. The same mechanism could occur in the case of the silver promoted acidic cesium salt of 12-tungstophosphoric acid in halide-free DME carbonylation. Thus, this study gave us understanding of the reason for the 100% increase in activity of Ag/Cs1.5H1.5PW12O40 catalyst as compared with Ag/Nafion, Ag/ZSM-5 and Ag/ SO4/ZrO2 catalysts (5-25%). It may be associated with the difference of v(CO) in the two catalysts: Ag/Cs1.5H1.5PW12O40 catalyst having a v(CO) of 2188 cm-1 and Ag/Nafion having a v(CO) of 2173 cm-1, and it is quite possible that cationic silver carbonyl clusters obtained in strong acid media are the most active in carbonylation reactions. Unauthenticated Download Date | 1/24/18 1:43 AM
Carbonylation of Dimethyl Ether on Ag/Cs1.5H1.5PW12O40
4 Conclusions The cationic silver carbonyl Ag(CO)+ on the surface of the acidic cesium salt of 12-tungstophosphoric acid was identified by in situ FTIR spectroscopy. The v(CO) of silver carbonyl was observed at 2188 cm-1. The reason for the increase in carbonylation activity of the Ag/Cs1.5H1.5PW12O40 catalyst as compared with the Ag/Nafion catalyst [8] may be associated with difference of v(CO) with values of 2188 and 2173 cm-1 respectively. The novel bifunctional catalyst Ag/Cs1.5H1.5PW12O40 is expected to have significant promise for practical use. Acknowledgements: This work was conducted within the framework of budget project No. 0303-2016-0004 of the Boreskov Institute of Catalysis. The authors are grateful to Ms. A.A Budneva for her assistance in the IR work.
References [1] Sunley G. J., Watson D. J., High productivity methanol carbonylation catalysis using iridium - The Cativa (TM) process for the manufacture of acetic acid, Catal.Today, 2000, 58, 293-307. [2] Shikada T., Ohno Y, Ogawa T., Ono M., Mizuguchi M., Tomura K., Fugimoto K., Direct Synthesis of Dimethyl Ether from Synthesis Gas, Stud. Sur. Sci. Catal., 1998, 119, 515-520. [3] Ellis B., Howard M. J., Joyner R. W., Reddy K. N., Padley M. B., Smith W. J., Heterogeneous catalysts for the direct, halide-free carbonylation of methanol, Stud. Sur. Sci. Catal., 1996, 101, 771-779.
61
[4] Cheung P., Bhan A., Sunley G. J., Iglesia E., Selective Carbonylation of Dimethyl Ether to Methyl Acetate Catalyzed by Acidic Zeolites, Angew. Chem. Int. Ed., 2006, 45, 1617-1620. [5] Wegman R. W., Vapour Phase Carbonylation of Methanol or Dimethyl Ether with Metal-ion Exchanged Heteropoly Acid Catalysts, Chem. Commun., 1994, 947-948. [6] Volkova G. G., Plyasova L. M., Salanov A. N., Kustova G. N., Yurieva T. M.,. Likholobov V.A, Heterogeneous catalysts for halide-free carbonylation of dimethyl ether, Catal. Lett., 2002, 80, 175-179. [7] Zagretdinova E. R., Volkova G. G., Silver or Copper Promotion of Catalysts Based on Acidic Cesium Salt of 12-Tungstophosphoric Acid for Dimethyl Ether Carbonylation, Chemistry for Sustainable Development, 2017, 25, 207-211. [8] Sauma Y., Tsumori N., Willner H., Xu Q., Mori H., Morisaki Y., Carbonylation of Hydrocarbons and Alkohols by Cationic Metal Carbonyl Catalysts, J.Mol. Catal., 2002,189, 67-77. [9] Williams C., Makarova M.A., Malysheva L. V., Paushtis E. A., Zamaraev K. I., Thomas J. M., Mechanistic Studies of the Catalytic Dehydration of Isobutyl Alcohol on NaH-ZSM-5, J. Chem. Soc. Faraday Trans., 1990, 86(20), 3473-3485. [10] Meijers S., Gielgens L. N., Ponec V., IR Spectroscopic Study of the Skeletal Isomerisation of Butene by Alumina-Supported Tungsten Oxide Catalysts, J.Catal., 1995, 156, 147-153. [11] Misono M. Unique Acid Catalysts of Heteropoly Compounds (Heteropolyoxometalates) in the Solid State, Chem. Commun., 2001, 13, 1141-1152. [12] Luzgin M. V., Kazantsev M. S., Volkova G.G., Wang W., Stepanov A. G., Carbonylation of Dimethyl Ether on Solid Rh-promoted Cs-Salt of Keggin 12-H3PW12O40: A Solid-State NMR Study of the Reaction Mechanism, J. Catal., 2011, 291, 72-79.
Unauthenticated Download Date | 1/24/18 1:43 AM
