Toluene chemisorption

A MgO-supported W—Pt catalyst has been prepared from IWsPttCOIotNCPh) (i -C5H5)2l (Fig. 70), reduced under a Hs stream at 400 C, and characterized by IR, EXAFS, TEM and chemisorption of Hs, CO, and O2. Activity in toluene hydrogenation at 1 atm and 60 C was more than an order of magnitude less for the bimetallic cluster-derived catalyst, than for a catalyst prepared from the two monometallic precursors. 

Nalewajski, R. F. and A. Michalak. 1995. Use of charge sensitivity analysis in diagnosing chemisorption clusters Minimum-energy coordinate and Fukui function study of model toluene-[V205] Systems. Int. J. Quantum Chem. 56 603-613. 

Fio. 6. Steric hindrance to dissociative chemisorption in the ortho position of toluene resulting in severe ortho deactivation. 

The presence of significant quantities of physisorbed water promotes the chemisorption of alkoxysilanes, especially of the ones with two or three alkoxy groups. Engelhardt and Orth90 reported that chemisorption of n-octyltriethoxysilane from a dry toluene solution on a dehydrated silica amounts 0.30 fimol/m2. However, if a toluene solution containing traces of water is used, the amount of chemisorbed silane increases up to 1.25 /tmol/m2. 

The process of oligo- and polymerisation can occur either on the surface of the wet silica or in the toluene solution. The formation of polylayered coatings was investigated in detail by Gorski et al.,91 reporting on the chemisorption of 3-methylacryloxypropyltrimethoxysilane from acetone solutions, containing various amounts of water. 

In order to circumvent this problem, Derouane et al. for acetylation reaction of anisole and toluene,[19,20] consider that the adsorption terms of the aromatic system represents only a physisorption process rather than also including chemisorption. This could be interpreted as the reaction not occurring between the two adsorbed species. 

Fig. 25. A1 ternative toluene chemisorption systems involving the bipyramidal surface cluster of vanadium pentoxide. The structures (a, c, e, g, i) represent molecularly adsorbed toluene, while the remaining systems (b, d, f, h) model the dissociative adsorption, with two methyl hydrogens chemically bonded to the surface oxygens at the pyramid bases. Asterisks indicate positions which give rise to unstable MEC. The three atoms of the parallel complex (i), marked with an arrow, denote the extra instabilities appearing when the closed-system constraint (d N = 0) is imposed. The results are taken from Ref. 8. At each diagram the (I, E) stability diagnosis is also indicated (see Fig. 24)...

In Fig. 35 we have compared the absolute charge displacement diagrams at all three levels of description, for the four chemisorption structures of Figs. 33 and 34. It follows from the CT patterns that at larger adsorbate-substrate separations (a, c, d) the direction of the inter-reactant CT is indeed the same as that assumed in Fig. 34, i.e., from toluene (B) to the surface cluster (A). However, at the closer approach (b) it is reversed, so that the cluster acts as a base and toluene becomes an acidic reactant. When the distance in panels (a, c, d) is decreased by 1 A, to become comparable to that in panel (b), a similar reverse CT is observed in the parallel structures fed), but the CT direction stays... 

Two methods have been proposed for the preparation of organosilane monolayers. One is chemisorption from organosilane solution [4-6], and the other one is Langmuir-Blodgett (LB) method or water-cast method [7-23], Fig. 1 shows the film formation mechanism of the organosilane by LB method (a) and chemisorption method (b). In the case of LB method (Fig. 1(a)), the toluene solution of organotrichlorosilane was spread on the water surface (pH 5.8) at a controlled subphase temperature. To attain quasi-equilibrium state of the monolayer, the monolayer was kept on the water subphase under a given... 

Toluene surface coordination chemistry was quite different from that of benzene. Toluene chemisorption on all the clean surfaces was thermally irreversible. In addition, toluene was not displaced from these surfaces by trimethylphosphine nor by any other potentially strong field ligand examined to date, e.g., carbon monoxide or methyl isocyanide. In the thermal decomposition of toluene on these surfaces (attempted thermal desorption experiments), there were two thermal desorption maxima for H2 (or D2 from perdeuterotoluene) with the exception of the Ni(110) surface. This is illustrated in Figure 6 for Ni(lll)-C7Dg. 

Stereochemical Features of Benzene and Toluene Coordination Chemistry. Benzene forms an ordered chemisorption state on the flat Ni(lll) and Ni(100) surfaces at 20°C with unit cells of (2/3x2/3)R 30° and c(4x4), respectively (13). The symmetry data do not fix the registry of the benzene with respect to the metal atoms nor the orientation of the ring plane to the surface plane. However, basic coordination principles would suggest that the benzene ring plane should be parallel to the surface plane. In Figures 8 and 9, possible registries of the benzene with respect... 

Silica-supported cobalt catalysts are accessible by ALE, after chemisorption onto silica of Co(acac)3 from the gas phase with a metal loading between 5.7 and 19. 5 wt% . The catalysts were tested for gas-phase toluene hydrogenation in a microreactor system. 

Auroux observed that ammonia adsorption shifts from strong chemisorption for HZSM-5 to a process controlled by physisorption (shorter h/i) for boron-modified zeolites. The acidity found by this method correlated well with the modified catalytic reactivity shown for methanol conversion, toluene/methanol alkylation, and toluene disproportionation processes. Stradella (129) utilized the above techniques to suggest that a dissociative chemisorption of ammonia takes place on the strongest Lewis sites of reduced Bi203-MoOj whereas only relatively weak coordination occurs in that same region of reoxidized samples. 

Chandler BD, Schnabel AB, Pignolet LH (2001) Ensemble size effects on toluene hydrogenation and hydrogen chemisorption by supported bimetaUic particle catalysts. J Phys Chem B 105 149... 

We have presented results for the dependence upon activation of the chemisorption of ammonia, carbon monoxide, carbon dioxide, and oxygen in Section VI, of hydrogenation and isomerization of hexenes and of exchange between deuterium and the ring and side chain of toluene in Section VII. Despite our attempts to control the activation conditions carefully there is a regrettable degree of scatter in our results. However, the bulk and surface condensations are clearly complicated in detail and the surface area of chromia is known to be a rather sensitive function of the exact details of activation (28). 

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