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

摘要

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(Ni3S2,PdS,Co9S8,Rh2S3,RuS2,PtS and MoS2)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,Rh2S3 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 Br0nsted-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.