Infrared Spectroscopy and Temperature-Programmed Desorption Study of Adsorbed Thiophene on γ-Al₂O₃

Abstract

The adsorption of thiophene (C4H4S) on γ-Al2O3 has been investigated in ultrahigh vacuum (UHV) using infrared (IR) spectroscopy and temperature-programmed desorption (TPD). Following thiophene adsorption onto γ-Al2O3 at 130 K, TPD reveals two peaks with maximum rates of desorption at 175 and ∼220 K. The former peak is assigned to desorption of multilayer thiophene while the latter peak is assigned to desorption of weakly chemisorbed thiophene from the alumina surface. IR spectroscopy of adsorbed thiophene at submonolayer coverages provides further evidence that thiophene interacts only weakly with the alumina support; no decomposition of the thiophene overlayer is observed upon heating to 600 K under UHV conditions or a partial pressure of thiophene of 3.0 Torr. Three kinds of adsorbed thiophene species exist on the alumina surface at saturation coverage: one in which thiophene interacts with hydroxyl groups, presumably via hydrogen bonding, a second in which thiophene is coordinated via its sulfur atom to coordinately unsaturated Al3+ sites on the surface, and a third species which is present only at high thiophene coverages. The heat of adsorption for thiophene on γ-Al2O3 has been determined under equilibrium conditions (P Th = 3.0 Torr) to be ΔH ads = −28.9 kJ/mol. A direct correlation has been established between the IR and TPD data, permitting integrated extinction coefficients to be determined for adsorbed thiophene in both the monolayer and multilayer coverage regimes. Extinction coefficients in the two coverage regimes are markedly different, underscoring the need to use care when interpreting the IR spectral intensities for adsorbed species. While, as expected, this study has shown that thiophene adsorbs only weakly on γ-Al2O3, more importantly it has shown that the combined IR−TPD methods can be used to determine both the thiophene coverage and the mode of bonding with the surface.

Adsorption and reaction of thiophene and H2S on Mo2C/Al2O3 catalyst studied by in situ FT-IR spectroscopy

“…The IR bands in the n CH region are quite similar in positions to those observed on Mo sulfide [24][25][26] and nitride 19,21 catalysts upon adsorption of thiophene/H 2 at high temperatures. So they can be also assigned to the vibrations of CH 2 and CH 3 groups of adsorbed C 4 hydrocarbon species 19,[21][22][23][24][25][26][27][28][29][30][31] that are derived from the HDS of thiophene.…”

ADSORPTION OF 4,6-DIMETHYLDIBENZOTHIOPHENE OVER Cu/ZrO2

“…These include desulfurization by microbial oxidation 6,7 , chemical oxidation 8,9 , ultraviolet-assisted oxidation 10 , biodesulfurization 11,12 , and adsorption [13][14][15][16][17] . In the adsorption process, sulfur compounds are removed via p-complexation [18][19][20][21][22] .…”

Selective Fabrication of Poly(3,4‐ethylenedioxythiophene) Nanocapsules and Mesocellular Foams Using Surfactant‐Mediated Interfacial Polymerization

“…It is quite clear from this data that the EDOT monomer has been successfully polymerized by the SMIP method. [13] In general, mineral acids such as sulfuric acid are required as dopants for the efficient polymerization of EDOT.…”