Thiophene adsorption

Figure 9.11 Thiophene adsorbed at 500 K on an H-atom pretreated MoS2 cluster (50 x 54 A2). Beam-like features at the metallic edge [scan line (i)] and the shifted intensity of the outermost edge protrusions relative to the clean edge (triangles refer to the clean edge). These shifts in intensity [line scan (ii)] are associated with changes in the local electronic structure after adsorption of thiophene observed with STM. All the images were taken at room temperature subsequent to thiophene adsorption at 500 K. (Reproduced from Ref. 34).

Several catalysts with various degrees of palladium loading and metal dispersions were submitted to thiophene adsorption. The dissociatively... 

Figure 7. Effect of temperature on butene and thiophene adsorption...

The importance of H2S adsorption from the point of view of the over-all reaction is shown by its effect on butene hydrogenation and on thiophene conversion (Figure 2). These indicate that H2S adsorption competes for sites which are essential to the reaction. Since its effect on thiophene adsorption was to cut peak delay by only 10 to 30%, it may be that H2S competes for hydrogen adsorption... 

Vcpor Phase Adsorption Benzene/Thiophene Adsorption Isotherms... 

Thiophene adsorption isotherms on all sorbents are compared in Figure 4. It is clearly seen that Ag-Y and Cu-Y could adsorb significantly larger amounts of thiophene even at very low pressures. 

In this work, vapor-phase benzene/thiophene adsorption isotherms were investigated to develop new sorbents for desulfurization. Among the sorbents studied, Cu(I)-Y and Ag-Y exhibited excellent adsorption performance (capacities and separation ctors) for desulfurization. This enhanced performance compared to Na-Y was due to the n-complexation of thiophene with Cu and Ag. Molecular orbital calculations confirmed the relative strengths of n-complexation thiophene > benzene and Cu > Ag. ... 

During the adsorption and desorption of thiophene on HZSM5 zeolites, reversible surface reactions of thiophene to unsaturated thiol-like species were found even at room temperature. Condensation reactions of thiophene to benzothiophene were observed over HZSM5 only but not over the NaZSMS samples [3]. Cleavage of the C-S bond and formation of SH surface groups were observed during thiophene adsorption on HY zeolites [4]. 

Layman KA, Bussell ME (2004) Infrared spectroscopic investigation of thiophene adsorption on silica-supported nickel phosphide catalysts. J Phys Chem B 108 15791... 

Chemical methods of determining the nature and surface concentrations of active components have also been attempted Mo oxide by butene adsorption and, in reduced catalysts, by oxygen chemisorptionM0S2 and/or active site concentrations by pyridine adsorption and thiophen adsorption and temperature-programmed desorption of thiopen cf. p. 200), surface acidity by NH3 adsorption cf. p. 199). Sulphides in a Ni-Mo/ AI2O3 catalyst have been characterized by differential thermal analysis of the catalyst in oxygen. ... 

On sulphided M0/AI2O3 stoicheiometric calculations and kinetic data showed that the catalytic activity for thiophen hds depended on the concentration of dual surface sites, anion vacancies for thiophen adsorption, and surface sulphide and/or oxide ions for hydrogen adsorption. The overall reaction was controlled by a surface reaction between adsorbed species on these sites. 

Richardeau et al. investigated thiophene adsorption from liquid solutions containing hydrocarbons over HFAU zeolites in a stirred batch system at room temperature.144 They found that the maximum number of thiophene molecules adsorbed per gram of zeolites is equal to their concentration of acidic sites and considered that the acidic sites are the adsorption sites. They further found that the presence of toluene causes a large decrease in the removal of thiophene, and when the concentration of thiophene is high (27.7 wt%), an acid-catalyzed condensation of thiophene occurs to form dimers, trimers, and tetramers, which remain trapped on the zeolite. They concluded that thiophene removal by adsorption on acidic zeolites could only be carried out from diluted solutions containing no olefinic compounds. 

The problem of decreased catalyst activity due to irreversible thiophene adsorption was solved numerically using an orthogonal collocation method with three internal points. The numerical results were compared with experimental data obtained by... 

Table 1. Thiophene Adsorption Amounts upon Saturation...

DFT has also allowed to obtain knowledge in the sites involved in HDS reactions. For instance, Moses and co-workers (145) have reported a DFT study on HDS of thiophene, and they have fovmd that the thiophene adsorption and subsequent hydrogenation of thiophene to 2,5-dihydrothiophene occurred at the Mo(lOiO) edge brim site, while direct desulfurization took place at the sulfur vacancies at the S(iOlO) edge. 

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