5244
J. Phys. Chem. 1986, 90, 5244-5249
oil has the advantage that the three-phase interval of the ternary system A-B-C is raised above the melting point so that the phase behavior of the system can be studied from 6 = t = 0 into the quinary system at ambient temperatures.
Acknowledgment. We are indebted to Mrs. H. Frahm, Dr. P.
Firman, Mr. B. Faulhaber, and Mr. T. Lieu for their assistance with the experiments. This work was supported by the German Federal Ministry for Research and Technology (BMFT). Registry No. SDS, 151-21-3; C,E,, 111-76-2; NaCI, 7647-14-5; noctane, 11 1-65-9.
Reactivity of Iron Carbonyl Complexes in a Hydrated Sodium-Y Zeolite Matrix and Catalysis of the Resulting Hydride Anion HFe3(CO)11'for Water-Gas-Shift Reaction+ Masakazu Iwamoto,* Shin-ichiro Nakamura, Hideto Kusano, and Shuichi Kagawa Department of Industrial Chemistry, Faculty of Engineering, Nagasaki University, Nagasaki 852, Japan (Received: January 27, 1986)
Iron carbonyls Fe(CO)5, Fe2(C0)9,and Fe3(C0)12have been introduced into a hydrated Na-Y zeolite. Fe(CO)5 was only weakly adsorbed on the zeolite. Fe2(CO), and Fe3(C0),, were reactive in the hydrated zeolite cages to yield a hydride anion species HFe,(CO),,- which was characterized by IR absorption bands at 2044, 1987, 1950, and 1645 an-', UV-vis spectrum at 540 nm, and gas-phase analyses. The red shift of absorption band of the bridging carbonyl indicated ionic interaction of a bridging carbonyl with an Ai3+ion in the zeolite matrix. The formation of the anion species was not observed in a dehydrated Na-Y zeolite, indicating the importance of water or a surface hydroxyl group in the reaction. The reaction course from di- or trinuclear iron carbonyl to the hydride anion has been studied by an ESR technique. Fe,(CO)*-, Fe(CO)L, and Fe3(CO)11species were detected as intermediates, and reaction schemes have been proposed. The resulting HFe3(CO)]I- was stable at or below 4.13 K both in a vacuum or in a CO atmosphere. Above this temperature it was gradually decomposed. Catalytic activity of the HFe3(CO)Il-species was examined for water-gas-shift reaction at 333-453 K and atmospheric pressure. The activity was very high and comparable to that reported in the homogeneous phase at high pressure. Kinetics and spectroscopic studies indicated that the reaction between HFe3(CO), and H 2 0 would be rate-determining.
Introduction Metal carbonyl compounds supported on inorganic materials' are attracting attention for purposes of, first, anchoring metal carbonyl clusters in efforts to develop a new chemistry in the interface between homogeneous and heterogeneous catalyses and, second, utilizing coordination complexes as precursors for the preparation of the assembly of highly dispersed metal atoms. This study has been correlated to the first point. We wish here to report on the remarkable difference between the behaviors of iron carbonyls in hydrated and dehydrated zeolites, detection of intermediates and elucidation of the grafting pathway, and catalysis of the resulting complex grafted in the zeolite. Although a large number of carbonyl-support systems have so far been reported in zeolites2t3as well as on oxides, all of these works have been carried out in rigorously dehydrated zeolites, as far as we are aware. The present work is the first example of the behavior of carbonyl clusters in hydrated zeolite and the catalysis of the carbonyl species produced on the surface. Hugues et al. have reported formation of the anionic hydride cluster [HF3(CO),,-]M+ through chemisorption of Fe(CO)5 or Fe3(CO),, on basic supports such as alumina or magnesia4 and have further studied the thermal decomposition of the resulting HFe,(CO), I - clusters.5 However, the grafting pathway from iron carbonyls to the hydride ion has not been much investigated. Zeolites usually have various cages distinguished, which is a very different property from surface of other inorganic supports such as alumina. Therefore, there is a possibility that it becomes easier by using zeolites to detect intermediates in the course of formation of stable carbonyl species on supports since the cage might be a room suitable for stabilizing intermediates. In this work the grafting pathways have been investigated mainly by means of ESR spectrometry on hydrated and dehydrated zeolites. 'The preliminary results have been reported as communications in the following papers: Chem. Lett. 1983, 1483; Inorg. Chem. 1983, 22, 3365; J . Inclusion Phenom. 1986, 4 , 99.
0022-3654/86/2090-5244$01.50/0
The catalysis of the HFe3(CO),,- species grafted in the zeolite by ionic interaction with an A13+ion will be reported in the last section. The water-gas-shift reaction (WGSR) was selected as a model reaction on the following bases. Recent investigations have shown that the WGSR can be carried out at temperatures lower than 473 K by using homogeneous catalysts,6-'0 which is consistent with the more favorable thermodynamic equilibrium. The relatively low turnover frequency for Fe(CO), makes it an unlikely practical catalyst even under ideal conditions.* However, the iron carbonyl-zeolite system is an exemplary model system (1) Bailey, D. C.; Langer, S. H. Chem. Rev. 1981, 81, 109. (2) Ballivet-Tkatchenko, D.; Coudurier, G. Inorg. Chem. 1979, 18, 558. (3) Gelin, P.; Coudurier, G.; Ben Taarit, Y.; Naccache, C. J. Caral. 1981, 70, 32. Goodwin, G. D.,Jr.; Naccache, C. J. Mol. Catal. 1982, 14, 259. Namba, S.; Komotsu, T.; Yashima, T. Chem. Lett. 1982, 115. Blackmond, D. G.; Goodwin, J. G., Jr. J. Chem. Soc., Chem. Commun. 1981,125. Huang, T.; Schwartz, J. J . Am. Chem. SOC.1982, 104, 5244. Ballivet-Tkatchenko,
D.; Coudurier, G.; Mozzanega, H. Catalysis by Zeolites; Imelii, 8. et al., Eds.; Elsevier: New York, 1980; p 309. Gelin, P.;Ben Taarit, Y.; Naccache, C. Proceedings of the 7th International Congress on Catalysis; Elsevier: New York, 1981; p 898. Tanaka, K.; Watters, K. L.; Howe, R. F.; Andersson, S. L. T. J . Catal. 1983, 79, 251. Schnoider, R. L.; Howe, R. F.; Watters, K. L. Ibid. 1983,79,298. Abdo, S.; Howe, R. F. J. Phys. Chem. 1983,87, 1713, 1722. (4) Hugues, F.; Basset, J. M.; Ben Taarit, Y.; Choplin, A.; Primet, M.; Rojas, D.; Smith, A. K. J. Am. Chern. Soc. 1982, 104, 7020. ( 5 ) Hugues, F.; Dalmon, J. A.; Bussiere, P.; Smith, A. K.; Basset, J. M.; Olivier, D. J . Phys. Chem. 1982, 86, 5136. (6) Kang, H.; Mauldin, C.; Cole, T.; Slegeir, W.; Pettit, R. J . Am. Chem. Sm. 1977, 99, 8323. Pettit, R.; Cam, K.; Cole, T.; Mauldin, C.; Slegeir, W. Adv. Chem. Ser. 1979, 173, 121. (7) King, R. B.; Frazier, C. C.;Banes, R. M.; King, A. D., Jr. J . Am. Chem. SOC.1978, 100, 2925. (8) King, A. D., Jr.; King, R. B.; Yang, D. B. J. Am. Chem. SOC.1980, 102, 1028. (9) King, A. D., Jr.; King, R. B.; Yang, D. B. J . Am. Chem. SOC.1981, 103, 2699 and references therein. (10) Ford, P. C. Arc. Chem. Res. 1981, 14, 31 and references therein. (11) Newsome, D. S. Catal. Rev.-Sci. Eng. 1980, 21, 275.
0 1986 American Chemical Society
Reactivity of Iron Carbonyl Complexes
The Journal of Physical Chemistry, Vol. 90, No. 21, 1986 5245
for the catalysis of immobilized metal carbonyls owing to the established reaction mechanism in solution6,8and is worth studying from this viewpoint.
Experimental Section Fe(C0)5 was obtained from Strem Chemicals and used as received. Fe2(C0)9and Fe3(C0)12were prepared by conventional methods and purified before use by sublimation. Na-Y was supplied by UCC (SK-40). Before adsorption of the iron complex, Na-Y was treated in the following way to prepare the hydrated Na-Y ("a-Y). Na-Y was heated slowly under vacuum (1.3 X Pa) to 673 K, exposed to oxygen (13.3 kPa, 1 h), and evacuated (1.3 X Pa, 1 h) at the same temperature. The zeolite was then rehydrated by the introduction of water vapor (2.4 kPa) at 298 K for 1 h and evacuated at 298 K (1.3 X lo-* Pa). Na-Y without the rehydration treatment in the above procedure is referred to as the dehydrated NaY (DNa-Y). The Na-Y zeolites were mixed with carbonyl complexes (2 mol of complex/mol of zeolite) under a nitrogen atmosphere and then mounted in each apparatus for IR, UV-vis, or ESR measurement or catalytic run. In the infrared experiments a self-supporting carbonyl/Na-Y wafer was placed parallel in a sample holder similar to that described elsewhere.'* Infrared spectra were obtained at 298 K by using a Jasco IR-8 10 spectrophotometer with a microcomputer system. Diffuse reflectance UV-vis spectra were measured by a Shimadzu UV-190 with an integrating sphere. The ESR spectra were measured at 298 or 123 K on a JEOL JES-FEIXG spectrometer after the sample was evacuated at 298 K for the desired period. Spin concentrations were determined by numerical double integration of the first derivative traces, with comparison to a standard single crystal of CuSO44H20. Simulated powder spectra were calculated by using a modified version of SIM 13.13 The catalytic run was carried out in a conventional closed recirculation system of 132 cm3. Unless otherwise stated, a sample mol of HFe3(CO)11-in 1.0 g of the Na-Y containing 7.81 X zeolite (HFe3(CO),,-/Na-Y = 1.33 mol/mol) was used. The pressure of H 2 0was maintained at 2.4 kPa during the reaction. The gases were analyzed by gas chromatography using N2or He as a carrier gas. Results and Discussion Stable Carbonyl Complexes on Hydrated and Dehydrated Nu-Y. When Fe(CO)5 was sublimed onto a HNa-Y zeolite, the zeolite became pale yellow. The IR absorption bands of C O were observed at 2098, 2013, and 1987 cm-', which were slightly shifted to lower frequencies compared to those of free Fe(C0)514and may indicate some interaction between the carbonyl ligands and the zeolite framework. Treatment under vacuum at 298 K, however, produced a solid that showed no v(C0) bands in the infrared spectrum and the white color of the mother zeolite. This indicates the low reactivity of the surface hydroxyl groups of the zeolite toward the carbonyl ligands of Fe(C0)5, which is quite consistent with the weak interaction of Fe(CO)5 with silanol groups of ~ilica.~J~ The Fe2(C0)9/HNa-Y system was warmed at 333 K in order to get a sufficient vapor pressure, and then the sample was evacuated at the same temperature for 30 min. The Na-Y became pink, and the generation of the anionic hydride species HFe3(C0)11grafted on the aluminum cation by ionic interaction was confirmed as follows. The adsorbed species showed an absorption maximum at 540 nm in the diffuse-reflectance UV-vis spectrum as shown in Figure 1, which is characteristic16 of HFe,(CO),,-. The IR spectrum of the species depicted in Figure 2 gave a shoulder of medium intensity at 2044 cm-I, two broad and intense (12)Lin, M.J.; Lunsford, J. H. J . Phys. Chem. 1975, 79, 892. (13)Lozos, G.;Hoffman, B.; Franz, B. QCPE 1974,No.265. (14)Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordinarion Compounds; Wiley-Interscience: New York, 1978;p 280. (15)Jackson, R.L.;Trusheim, M. R. J. Am. Chem. Soc. 1982,104,6590. (16)Heiber, W.; Beutner, H. 2.Naturforsch., 8: Anorg. Chem., Org. Chem., Biochem., Biophys., Bioi. 1962, 178, 211.
I
1
I
I
I
I
I
I
200
400 600 80 0 WAVELENGTH / n m Figure 1. Diffuse reflectance UV-vis spectra of "a-Y (a) and HFe3(CO),,-/HNa-Y after the adsorption of Fe2(C0)9at 333 K (b) or after the WGSR a t 373 K (c). Spectra were recorded with the zeolites in the form of loose powders contained in a vacuum-tight quartz cell. The DRS are reported as plots of the Kubelka-Munk function F ( R m ) , vs. wavelength.
I
I
I
I
I
2000 1600 120 WAVENUMBER I cm-1 Figure 2. Infrared spectra in the linear and bridging carbonyl region of the "a-Y background (a), after the adsorption of Fe2(CO), on the "a-Y at 333 K (b), and after the WGSR at 393 K (c), 2800
bands at 1987 and 1950 cm-' for the linear carbonyls, and a band of medium intensity at 1645 cm-I in the bridging region. The values are in agreement with those for [NR,] [HFe3(C0),l]17and HFe3(CO)11-supportedon a l ~ m i n a The . ~ shift of about 50 cm-' to lower frequency of the v(C0) band of the bridging carbonyl is due to the interaction between the aluminum cation and the oxygen lone pair of a coordinated C0.4s's The small red shifts (17) Wilkinson, J. R.;Todd,L. J. J. Organomet. Chem. 1976,118, 199. Hodali, H. A.; Arcus, C.; Shriver, D. F. Inorg. Synth. 1980,20, 218. The [NEt4][HFe3(CO),,] complex gives v(C0) bands at 2073 (w),2008 (s), 2000 (s), and 1709 (m) cm-' in C6H6solvent. (18)For example: Alich, A.; Nelson, N. J.; Strope, D.; shriver, D. F. Inorg. Chem. 1972,1I,2916. Kristoff, J. S.;Shriver, D. F. Inorg. Chem. 1974, 13,499. Shriver, D.F.; Onaka, S.;Strope, D. J . Organomet. Chem. 1976, 177, 277.
5246 The Journal of Physical Chemistry, Vol. 90, No. 21, 1986
Iwamoto et al.
of the v(C0) bands corresponding to the linear carbonyls are presumably attributable to the inner electrostatic fields of the zeolites. l 9 An analysis of the gas phase during the adsorption showed the presence of 0.93 mol of CO, 0.04 mol of C 0 2 , and 0.03 mol of H2 per F%(CO)9 adsorbed. The basic character of the hydroxyl groups on alumina20,21and on alkali-metal cation-exchanged zeolite22 has been shown. Reaction 1, similar to the formation 3Fe2(C0)9
+ 20H-
-
2HF3(CO)II-+ 3CO
+ 2C02
3 I
(1)
of HFe3(CO)11-from Fe3(CO)12in basic soluti0n,2~was concluded for the grafting of Fe2(C0)9on the zeolite lattice. The appearance of IR bands at 1405 and 1350 cm-I during the adsorption indicates that most of the C02 remains adsorbed on the zeolite as a hydrogen carbonate anion (eq 2). The small amount of H2produced C02
-
+ OH-
HC03-
(2)
has been concluded to result from the WGSR, since the HFe3(CO),
