Effect of phosphorus addition on the behavior of CoMoS/Al2O3 catalyst in hydrodesulfurization of dibenzothiophene and 4,6-dimethyl dibenzothiophene

The hydrodesulfurization (HDS) activity of phosphorus-added CoMoS/Al2O3 cat alysts has been examined using dibenzothiophene (DBT) and 4,6-dimethyldiben zothiophene (4,6-DMDBT) as reactants. Phosphorus modifies catalytic behavio r in two ways: increase of active sites by enhanced metal dispersion and in crease of Bronsted acidity. These effects yield a different distribution of products depending on the reactants. In thiophene HDS, phosphorus increase s only the conversion. In DBT HDS, phosphorus increases the conversion and produces more cyclohexylbenzene (CHB) than biphenyl (BP). In 4,6-DMDBT HDS, the conversion also increases but more dimethylbiphenyl (DMBP) is produced than methylcyclohexyltoluene (MCHT), the opposite trend from the one obser ved in DBT HDS. This is due to enhanced acidity of the catalyst, which allo ws migration of the methyl groups in 4,6-DMDBT. Maximum conversions are obt ained when the phosphorus content is proper, 0.5 wt.% in this study. (C) 19 99 Elsevier Science B.V. All rights reserved.