Hydrodesulfurization enhancement of heavy and light S-hydrocarbons on NiMo/HMS catalysts modified with Al and P

Deep hydrodesulfurization (HDS) of oil fractions is a key process in petroleum refineries due to the increasing demand for S-free diesel and gasoline fractions. In this work, a series of NiMo catalysts supported on Al- and P-modified HMS mesoporous substrate were tested in the HDS of thiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to evaluate the effect of Al and P additives on the catalyst response in HDS reactions (thiophene at I bar and 4,6-DMDBT at 5.5 MPa). The catalysts were characterized by a variety of techniques (XRD, N-2 adsorption-desorption, TPR, TPS, FT-IR of adsorbed pyridine, UV-vis and H-2 chemisorption). NiMo/Al-HMS-P catalyst containing 1.0 wt.% of P exhibited the best performance in both HDS reactions as a consequence of the proper balance between the active phase dispersion and the largest hydrogenation ability among the studied catalysts. The 4,6-DMDBT HDS reaction proceeded toward direct desulfurization (DDS) and hydrogenation (HYD) reaction routes. Concerning the HDS of thiophene, the increase of the catalyst acidity led to the formation of butadiene and diminished the hydrogenation of olefins (formation of butane). At the reaction temperature of 320 degrees C, the NiMo/Al-HMS-P1.0 catalyst exhibited the highest activity and the lowest butane formation among the catalysts studied. The isomerization of olefins in the thiophene HDS reaction did not occur, in line with the observed absence of isomerization in the 4,6-DMDBT HDS reaction. (C) 2014 Elsevier B.V. All rights reserved.