Summary:The hydrogenolysis reaction of dibenzothiophene over molybdenum sulfide, tungsten sulfide, cobalt sulfide, and nickel sulfide catalysts were studied by means of a batch method. From the experimental results, the following conclusions were obtained.
The mechanism of the desulfurization of the polynuclear thiophene compounds with a Raney nickel was studied in ethanol at atmospheric pressure and from 0 to 78.3 °C. The desulfurization rate was initially fast but reached zero in about 30 minutes. The major products were biphenyl in the desulfurization of dibenzothiophene (1), 1-phenylnaphthalene in the desulfurization of benzo[b]naphtho[1,2-d]thiophene (2), and 2-phenylnaphthalene in the reaction of benzo[b]naphtho[2,3-d]thiophene (3) and benzo[b]naphtho[2,1-d]thiophene (4). The desulfurization extent for the four compounds decreased in this sequence: 3>1>2>4. The extent of the desulfurization of the polynuclear thiophene compound was not related to the reaction indices, Fr(E), Fr(N), and Fr(R), of the sulfur atom of the compounds, which were calculated by using a simple Hückel theory; rather, it was related to both the free valence and the π-electron density. Therefore, the polynuclear thiophene compounds were considered to adsorb on a Raney nickel through the free-electron pair of the sulfur atom; consequently, the adsorption led to the C–S bond scission.
Desulfurization of polynuclear thiophenes was performed by contin uous stirring with a Raney nickel catalyst in ethanol at 0-78.8 °C. The major products were biphenyl in the desulfurization of diben zothiophene, α-phenylnaphthalene in the desulfurization of benzo[b]naphtho[1,2-d]thiophene, and β-phenylnaphthalene in the desulfurization of benzo[b]naphtho[2,3-d]thiophene and benzo[b]naphtho[2,1-d]thiophene. Observation of these products shows that the main reaction pathway is the extrusion of a sulfur atom to give the corresponding hydrocarbon. The π-electron densities of the sulfur atoms, which were calculated by using simple Hückel molecular orbital theory, are considered to be related to the adsorption of the sulfur compounds to the surface and consequently to the C-S bond-breaking rate.
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