The reaction between thiophene and hydrogen on the hexagonal hydrate of molybdenum oxide

Abstract

In the catalytic reaction between thiophene and hydrogen on the hexagonal hydrate of molybdenum trioxide, the catalyst reacted with the reactant gas and the change of the state took place at the early stage of the reaction ('aging stage'). To study the mechanism of the catalytic reaction, the changes in the conversion of thiophene and the composition of the reaction products were studied by the flow method at the reaction temperatures of 350°, 375° an 400℃. The main products of the hydrodesulfurization of thiophene were n-butane, 1-butene, trans-2-butene, cis-2-butene and hydrogen sulfide. At the early stage of the reaction, the conversion of thiophene and the concentration of n-butane rapidly increased to maxima and decreased to steady values, while the concentration of butenes simply increased to steady values. The catalyst used for the hydrodesulfurization was studied by ESR spectroscopy and the signal due to Mo(V) was observed. The intensity due to Mo(V) increased at first, decreased through a maximum, and increased again to a steady value. At the first half of the aging stage. Mo(V) was formed by the reduction of MoO_3, while, at the steady stage, Mo(V) was produced by the sulfurization of the catalyst. From the results obtained by ESR studies, in addition to the results of the conversion and the changes of the state of the catalyst, the author concluded that the reaction was composed of two independent processes. One is the process in which thiophene is adsorbed on Mo atom by the coordination of sulfur atom and is hydrogenated to give n-butane and higher sulfide of the catalyst. The other is the process that thiophene adsorded parallel to the surface of the catalyst with four carbon atoms is catalytically hydrogenated to C_4-products through butadiene. The catalytic actity of the catalyst for the hydrodesulfurization of thiophene depends on the Mo(V) in the sulfide.