Vibrational Study of Organometallic Complexes with Thiophene Ligands:  Models for Adsorbed Thiophene on Hydrodesulfurization Catalysts

Abstract

Interpretation and comparison of the vibrational spectra of organometallic complexes containing thiophene ligands with IR spectra of adsorbed thiophene on sulfided Mo/Al2O3 catalysts have permitted a definitive assignment of the adsorption mode of the surface-bonded thiophene. Infrared and Raman spectra were acquired for three organometallic complexes: (η5-C5D5)Re(CO)2(η(S)-C4H4S), (η5-C4H4S)Cr(CO)3, and [(η5-C4H4S)Mn(CO)3]BF4. The vibrational properties of η1(S)- and η5-coordinated thiophene were further investigated through normal-mode analyses of the IR spectra of thiophene coordinated in (η5-C4H4S)Cr(CO)3 and (η5-C5D5)Re(CO)2(η1(S)-C4H4S). Perturbations among the force constants of a gas-phase thiophene model, consistent with the structure of η1(S)- and η5-coordinated thiophene ligands, gave rise to respective thiophene force fields that allowed for the accurate determination of the IR spectra of thiophene coordinated in the Cr and Re complexes. Spectral shifts observed for the IR spectrum of the η1(S)-coordinated thiophene ligand, with respect to the IR spectrum of free thiophene, are similar to those observed for analogous bands of thiophene adsorbed at the surface of sulfided Mo/Al2O3 catalysts. Furthermore, perturbations among the force constants of η1(S)-coordinated thiophene, necessary to model such shifts, indicate that the hydrocarbon backbone of thiophene is strengthened upon η1(S) adsorption, whereas the C−S bonds are significantly weakened. These bonding changes, along with the assignment of the adsorption mode of thiophene, suggest an HDS mechanism in which the initial steps are η1(S) adsorption of thiophene followed by subsequent cleavage of one of the C−S bonds.

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

“…Evacuation at RT of the sample treated at 773 K produced great decrease in intensity in the 2800-3000 cm À1 regions. 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.…”

Catalytic Hydrodeoxygenation of Methyl-Substituted Phenols: Correlations of Kinetic Parameters with Molecular Properties

“…53 This requires a vacancy (Lewis acid site) on the catalyst to accept an electron pair of the O atom to facilitate the C-O bond cleavage. Earlier, we explained that under our H 2 S/H 2 conditions, the catalyst surface should have many such vacancy sites available.…”

Catalyst nanoparticle growth dynamics and their influence on product morphology in a CVD process for continuous carbon nanotube synthesis

“…3a. The strong peak centred at ~710 cm -1 is characteristic of the out-of-plane wagging motion (ω oop ) of the C-H bond within the thiophene molecule, and is henceforth used as a reference marker to indicate its presence [26]. Increasing the furnace temperature to 750°C causes a decrease in intensity of the key thiophene band; this is also accompanied by the early onset of a doublet, an alkyne C triple bond stretch at ~2150 cm -1 (triple bond stretches are in the range of 2100-2180 cm -1 ) [27].…”