Selective hydrogenation and defunctionalization of heavy oil model compounds using an unsupported iron catalyst

Abstract

Developing practical, inexpensive catalysts for the partial upgrading of crude oil is essential for converting heavy oil to meet pipeline standards without diluent. Here we report that air-stable unsupported iron sulfide nanoparticles derived from a single-source homogeneous precatalyst, Fe2S2(CO)6, are highly effective catalysts for the partial hydrogenation of substituted anthracenes and aromatic nitrogen and sulfur heterocycles. The reactivity of the anthracene series is governed by stereoelectronic effects imposed by the phenyl substituents, decreasing in the order anthracene > 9-phenylanthracene > 9,10-diphenylanthracene. Nitrogen- and sulfur-containing heterocycles are partially hydrogenated, with limited heteroatom removal for benzothiophene, showing that the unsupported iron sulfide catalyst is well-suited for the selective partial hydrogenation and limited defunctionalization, which are key for catalytic partial upgrading of heavy petroleum. The unsupported iron sulfide nanoparticles also catalyze hydrogenation of mixed “feeds” comprising combinations of model compounds, demonstrating that carbocyclic and heterocyclic molecules can be processed simultaneously with little self-inhibition of overall activity, a key requirement for compositionally challenging bitumen feeds. Several techniques were used to characterize the iron sulfide nanoparticles, as well as the organic reaction products. The heterogeneous catalyst, generated in situ, was more active than a ball-milled commercial iron sulfide catalyst. The heterobimetallic precatalyst Co2FeS(CO)9 does not enhance the rates of hydrogenation.