Microkinetic interpretation of HDS/HYDO selectivity of the transformation of a model FCC gasoline over transition metal sulfides

The conversion of a model FCC gasoline (composed of 2-methylthiophene (2MT), 2,3-dimethylbut-2-ene (23DMDB2N) and orthoxylene in n-heptane) under realistic hydrodesulfurization (HDS) conditions was investigated over a serie transition monometallic sulfides (Ni(3)S(2), PdS, Co(9)S(8), Rh(2)S(3), RuS(2), PtS and MoS(2)) and unsupported transition bimetallic sulfide catalysts (NiMoS and CoMoS). The results reveal for the first time that a volcano curve relationship exists between the ab initio calculated sulfur-metal bond energy, E(MS), descriptor of bulk TMS and their activities in olefin hydrogenation and in alkylthiophene desulfurization measured simultaneously. In particular, Rh(2)S(3) with an intermediate sulfur-metal bond energy of 119 kJ/mol is the most active catalyst in both case hydrogenation of the olefin and in HDS of a sulfur compound. Furthermore, the HDS/HYDO selectivity which is the most important parameter in the deep HDS of gasoline, presents a maximum for the NiMoS catalyst with E(MS) of 128 kJ/mol. A microkinetic model based on Bronsted-Evans-Polanyi relationships and the competitive adsorption of the sulfur molecule and alkene on the catalytic site is proposed to give a rational interpretation of the experimental catalytic results. (c) 2007 Elsevier B.V. All rights reserved.