J. Phys. Chem. 1980, 84, 2891-2895
2891
Radical Formatlon and Radiation Damage in Adamantane Roger V. Lloyd," Department of Chemistty, Memphis State University, Memphis, Tennessee 38 152
Sllvlo DlGregorlo, Louis DIMauro, and David E. Wood Department of Chemistty, University of Connecticut, Storm, Connectlcut 06268 (Received;May 16, 1980; In Final Form: July 15, 1980)
Unelquivocal samples of the l-adamantyl (l-Ad) and 2-Ad radicals have been prepared in a matrix of adamantane (Ad)l by the simultaneous deposition of atomic sodium, 1- or 2-bromoadamantane,and adamantane at 77 K. The EPR spectrum of the l-Ad radical contrary to previous reports has a clearly resolved hyperfine structure that can be analyzed in terms of the solution parameters of Krusic et al., and the spectrum of the 2-Ad radical is identical with that previously reported by Ferrell et al. It is also shown that conditions of purification and irradiation can greatly affect the spectra obtained upon X irradiation of Ad itself. Depending upon conditions, alicyclic radicals that are primary producta of ring-opening reactions or benzylic-typeradicals that are probably secondary reaction products can also be obtained in addition to 1-Ad and 2-Ad radicals.
of double recrystallization with activated carbon in hexane Introduction (go% alicyclic radical stable to 245 K (B and M, Figures 3 and 4)
TFPBQ radical
+ polymeric products
(stable to 400 K, Figure 4) It must be emphasized that Ad efficiently occludes small traces of unsuspected impurities and that the presence of impurities, although they may not form stable products, may alter the relative yields and to a small extent the stability of the radicals produced by ionizing radiation. In summary, we believe that adamantane X-irradiated at 77 K produced mostly 1-Ad radicals with resolvable hyperfine splittings plus a small yield of 2-Ad radicals and an alicyclic radical that is probably a ring-opening primary radiation damaging product. Upon warming or upon irradiation at higher temperatures, the observed radicals are a benzylic radical and a radical with no hfs that we assign to secondary reaction products. References and Notes (1) (a) Bennett, J. E.; Mile, B. Trans. Faraday SOC.1971, 67, 1587. (b) Camaioni, D.; Waiter, H. F.; Jordan, J. E.; Pratt, D. W. J . Am. Chem. Soc. 1973, 95, 7978. (c) DiGregorb, S.; Yim, M. B.; Wood,
J. Phys. Chem. 1980, 84, 2895-2898
(2) (3) (4) (5) (6)
(7) (8) (9)
D. E. ha.1973, !E, 8455. (d) Helcke, G. A,; Fantechi, R. J. Chem. Soc., Faraday Trans. 2 1974, 1912. (e) Ling, A. C.; Kevan, L. J . Phys. Chem. 1976, 80, 592. (f) Lloyd, R. V.; Rogers, M. T. J. Am. Chem. SOC. 1973, 95, 2459. (9) Richerzhagen, T.; Svejda, P.; Volman, D. H. J. Phys. Chem. 1973, 77, 1819. (h) Symons, M. C. R.; Smith, S. G, J. Chem. SOC., Perkin Trans. 2 1979, 1362. Lloyd, R. V.; Woocl, D. E. J . Chem. Phys. 1974, 60, 2684. Jordan, J. E.; Pratt, D. W.; Wood, D. E. J . Am. Chem. SOC.1974, 96. 5588. Bowers, K. W.; Nolfi, G. J., Jr.; Greene, F. D. J. Am. Chem. SOC. 1963, 85, 3707. Jones, M. T. J. Am. Chem. SOC. 1966, 88, 174. Gee, D. R.; Fabes, L.; Wan, J. K. S. Chem. Phys. Lett. 1970, 7 , 311. Bonazzola, L.; Marx, R. Chem. Phys. Lett. 1971, 8 , 413. Filby, W. G.; Gunthler, K. Z. Nafurforsch. B. 1972, 27, 1289; Chem. Phys. Lett. 1972, 14, 440. Marx, R. Chem. Phys. Lett. 1972, 17, 152.
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(10) Krusic, F. J.; Rettig, T. A.; Schleyer, P. V. J. Am. Chem. Soc. 1972, 94, 995. (11) Ferrell, J. R.; Holdren, G. R., Jr; Lloyd, R. V.; Wood, D. E. Chem. Phys. Lett. 1971, 9 , 343. (12) Lloyd, R. V.; Rogers, M. T. Chem. Phys. Lett. 1972, 77, 428. (13) Hyfantis, G. J.; Ling, A. C. Chem. Phys. Lett. 1974, 24, 335; Can. J . Chem. 1974, 9 , 343. (14) Dismukes, 0. C.; Willard, J. E. J . Phys. Chem. 1976, 80, 1435. (15) Migita, C. T.; Iwaizuml, M. Chem. Phys. Lett. 1980, 71, 332. (16) Wood, D. E.; Lloyd, R. V. J . Chem. Phys. 1970, 53, 3932. (17) Yim, M. B.; Wood, D. E. J . Am. Chem. SOC. 1976, 98, 2053. (18) Yim, M. B. Ph.D. Thesis, University of Connecticut, Storrs, CT, 1974. (19) Lloyd, R. V.; Wood, D. E. J . Am. Chem. SOC.1975, 97, 5986. (20) Bennet, J. E.; Summers, R. Trans. Faraday SOC.1975, 69, 1043. (21) Yim, M. B.; Wood, D. E. J. Am. Chem. SOC.1975, 97, 1004. (22) McCall. D. W.: Doualass. D. C. J . Chem. Phvs. 1960. 33, 777. (23j Tabushi, T.; Aoyama, Y.;'Kojo, S.; Hamuro, J.;?Yoshida,Z.J . Am. Chem. SOC. 1972, 94, 1177.
ESCA Studies of Methanation Catalysts Derived from Intermetallic Compounds Roliand L. Chin, Azra Elattar, W. E. Wallace, and David M. Hercules# Department of Chemistry, Universiiy of Pittsburgh, Plttsburgh, Pennsylvania 15260 (Received: J m ~ a l y14, 1980)
ESCA measurements have been performed on several catalysts: (1)MNi5 (M = Th, U, or Zr), which under reaction conditions convert to Ni/M02; (2) Ni/Th02 prepared by conventional means; and (3) ThCo5which converts during reaction to Co/Th02. All except the conventionally formed Ni/Th02 show surfaces rich in the transition metal, accounting for the high methanation activity of these materials. The ESCA results show that the surface of the Ni/ThOz conventionallyformed catalyst is very low in Ni, thus providing an explanation of its weak catalytic activity. Exposure of the MNi5 systems to Hzor mixtures of H2 and CO enhances the surface enrichment of Ni. This is ascribed to the strong interactions between Ni and H or CO. Introduction In previous work, principally from this laboratory, a number of intermetallic compounds involving rare earths or actinides combined with Fe, Co, or Ni have been studied in relation to the catalytic conversion of CO/H2 mixtures into hydrocarbons.L'-10It has been observed that under reaction conditions the intermetallic compound is extensively transformed into rare earth or actinide oxide plus Fe, Co, or Ni. The evidence indicates that the active catalyst is this mixture rather than the original intermetallic compound, The work thus constitutes in part a new way of producing oxide-supported catalysts. These new catalysts exhibit exceptional activity compared with supported catalysts formed by the conventional wet chemical (impregnation-calcination) technique.'l Decomposed ThNi5 is one af the more active methanation catalysts. At 205 "C it exhibits a turnover number about an order of magnitude higher than Ni supported on A1203or Si02. Moreover, it is very much more active than Ni supported on Tho2prepared by conventional wet chemical technique^.^ For example, decomposed ThNi, at 300 "C converted essentially 100% of the CO in a synthesis gas mixture to methane, whereas Ni/Th02 prepared by impregnation under similar conditions converted less than 1%in a single pass reactor. Elucidation of the striking difference in Ni/Th02 catalysts found in the two different ways was the central feature to which the present study was addressed. As is indicated below, the factors responsible for the differences have been fully clarified. In an earlier study, intermetallic compounds having the composition MNi5 (M = U or Zr) were investigated as methanation catalysk2 As in the case of ThNi5, there was decomposition into metallic Ni and MOz. However, these catalysts were found to exhibit significant differences, (see 0022-3654/80/2084-2895$01 .OO/O
TABLE I: Catalytic Behavior of t h e Catalysts S t u d i e d catalyst
ThNi UNi ZrNi, Ni/ThO, Thco, Thco,
% CO converted a t 3 0 0 "C
- 100
12.5 5.3 negligible
