Benzene adsorbed

Amount of benzene adsorbed at 20 C on carbon black and on active carbons at low pressures, relative to the amount adsorbed at p/p = 0-175... 

Changes in relative peak intensity and marginal line shifts have been observed for benzene adsorbed on porous glass (26). More significantly, infrared spectroscopic evidence had been found in the appearance of inactive fundamentals for the lowering of molecular symmetry of benzene on adsorption on zeolites (47). 

Cyclohexadiene and benzene form identical structures on Pt(l 1 1) at low pressures (Figures 7.23 and 7.24). 1,3-Cyclohexadiene dehydrogenates to form benzene on the surface, while benzene adsorbs molecularly. Figure 7.24b schematically shows the adsorbed benzene structure at low pressure. The STM images of the C6 cyclic hydrocarbons show three different adsorbed structures on Pt(l 1 1). Cyclohexene and cyclohexane partially dehydrogenate to form rc-allyl, 1,4-cyclohexadiene adsorbs in a boat configuration, and both 1,3-cylohexadiene and benzene adsorb as molecular benzene on the surface. 

Fig. 1. The variation of the amount of benzene adsorbed on nickel and on platinum as a function of temperature. From Tetenyi and Barbernics (8), with permission.

Fig. 2. (a) Magnetization-volume isotherms for the chemisorption of hydrogen and of benzene on kieselguhr-supported nickel at 150° C (16). (b) Average number of bonds formed by benzene adsorbed on nickel-silica as a function of temperature (17). From J. Amer. Chem. Soc. 79, 4637 (1957) 83, 1033 (1961). Copyright by the American Chemical Society. Reprinted by permission of copyright owner. 

When benzene adsorbed on silica gel was irradiated with 7 rays, a rather complex symmetric spectrum was observed. The spectrum consisted of a triplet of about 48 G splitting with each component being further split into a quartet of lines. The latter splitting was about 10.6 G. This spectrum is attributed to the cyclohexadienyl radical (I) which is formed by the... 

The radical cation of benzene has been produced by y irradiation of benzene adsorbed on silica gel (62, 63). The seven-line spectrum shown in Fig. 24 is expected for a molecule having six equivalent protons. An experimental coupling constant of 4.4 G, compared to a value of 3.75 G for the negative ion, gives strong support for attributing the spectrum to a positive ion. The g value is also consistent with this assignment. 

EELS has been used to study the kinetics of relatively slow surface reactions, such as the hydrogen-deuterium exchange in benzene adsorbed on platinum [54], In... 

A carbon dioxide yield of 40.8% was achieved when benzene adsorbed on silica gel was irradiated with light (Z >290 nm) for 17 h. 

A large number of organic molecules have been imaged by STM with atomic resolution. In this sense, the STM opens a new era of organic chemistry. An example is the STM imaging of benzene, adsorbed on the Rh( 111) surface with the presence of CO (Fig. 1.17). The benzene molecules form a regular... 

Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the differences in adsorption strength are reflected in the electronic structure of the adsorbate-substrate complexes as determined based on the XAS and XES spectra for benzene on Cu(l 10) and Ni(100) shown in Figures 2.39 and 2.40, respectively [83,90]. 

Bull et al. (97) reported a systematic 2H-NMR and MD study of siliceous faujasite. MD calculations were performed for 1 molecule of benzene adsorbed in a single unit cell of faujasite. Full framework flexibility was incorporated, using potential parameters from MSI s cff91 force field (5). Simulations were performed for diffusion at 298, 350,400, and 450 K, using a time step of 1 fs for a 25-ps calculation run (following 5 ps of equilibration). 

There is general agreement, based on measurements of vibrational spectra taken at room temperature or below, that benzene adsorbs nondissocia-tively on single-crystal metal surfaces with the C6 ring oriented parallel or near-parallel to the surface. Furthermore, there is a strong general resem-... 

Fig. 10. Infrared spectra of benzene adsorbed on Pt/Si02 at room temperature after 30 min of evacuation, after being in contact with 300 Torr H2 for 16 h (the dashed spectrum is from gas-phase cyclohexane), after pumping for 10, 30, and then 50 min, and after reentry of 300 Torr H2 for 16 h. [From Ref. 248.]...

Haaland also measured the infrared spectra of benzene adsorbed on Pt/Al203 that had been regenerated after previous benzene/cyclohexane adsorptions (247) the surface was thought to retain structured carbonaceous deposits. In this case, the broad yCH feature was centered at ca. 3030 cm 1 (with components at 3042, 3031, 3024, and 3014 cm 1) rather than 3040 cm 1 for the species on the freshly prepared catalyst, and a weaker companion band occurred at 2947 cm-1. The benzene absorption bands at wavenumbers <1500 cm 1 were little changed in position but become more prominent in room-temperature spectra in which the 2947-cm 1 feature was weakened. Spectra measured over the range 300-650 K showed that the 2947-cm 1 feature disappeared at 435 K, whereas the vCH aromatic bands retained considerable intensity at temperatures up to 560 K. 

Fig. 12. Raman spectra of benzene adsorbed on (A) Ni/Si02 excited at 5145 A and (B) Pt/Si02 excited at 4880 A. [From Ref. 337, Z. Anal. Chem., W. Krasser, P. S. Bechthold, and U. Kettler, 314, 319, Figs. 3 and 4, 1983. Copyright 1983 Springer-Verlag.]...

Assignments of the Infrared and Raman Spectra of Benzene Adsorbed on Oxide-Supported Platinum and Nickel... 

A few very broad Raman bands at ca. 2960, 2750, ca. 1000 (shoulder), and ca. 800 cm-1 have been reported for benzene adsorbed on Rh/Al203 (344). An 776-C6H6 bonding mode has been suggested. Evacuation and subsequent coadsorption with CO lead to a changed spectrum of the type identified earlier as indicative of-(CH = CH) - in polymers. 

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