Promoter effect of nickel in thiophene hydrodesulfurization as monitored by sulfur uptake and cyclohexane conversion

Abstract

Hydrodesulfurization (HDS) activity and activation energy (e 0 TH ) values were determined and compared with irreversible sulfur uptake (S irr ) by 5 Al 2 O 3 -supported (MoO x , Ni and three NiMoO x ) catalysts and, in unsulfided form with the cyclohexane conversion activity. Synergy between Ni and Mo in catalytic activity and a correlation between HDS activity and the amounts of S irr was found. Some explanations for the differences in catalytic behavior of the different samples are presented.

Interaction affinity of nickel promoted molybdena alumina with C, H and S in some catalytic conversions

“…A positive correlation was observed there between HDS activity and cyclohexane conversion rates on the reduced, Ni-containing samples. It has also been reported [1] that significantly lower apparent activation energy values of thiophene HDS e 0 TH À Á were obtained for the samples of 0.35 and 0.6 Ni:Mo ratio than those for Ni:Mo of 0.15 ratio and Ni. It was assumed that this difference between the two catalyst pairs was a consequence of the different types of catalytic active sites for HDS on the different Ni-containing samples, indicated by literature data [2][3][4].…”

“…In a previous paper [1], we reported results of a study on thiophene hydrodesulfurization (HDS) rates and activation energy values determined for molybdena-alumina (Mo12), alumina supported Ni (Ni12) and three Ni promoted molybdena-alumina samples of different Ni:Mo ratio NiMo(0.X). A positive correlation was observed there between HDS activity and cyclohexane conversion rates on the reduced, Ni-containing samples.…”

“…A similar correlation in the activation energies of cyclohexane conversion values ðe 0 CH Þ would support the assumption on different types of active sites in the two catalyst pairs. It is of interest to determine and compare the cyclohexane conversion activation energies on the Ni-containing samples applied in [1]. Similarities in activation energy sequences in cyclohexane conversion and thiophene HDS would indicate the important role of the surface Ni content of the samples before sulfidation in the HDS activity of sulfided forms.…”

“…The NiMo(0.X) samples were found to be active in cyclohexane dehydrogenation to benzene at 573 K [1]. NiMo(0.35) and NiMo(0.6) also catalyzed the hydrogenolysis of C-C bond(s) producing hydrocarbon(s) of carbon number \ 6.…”

“…-to determine the apparent activation energy values, e 0 B and e 0 C\6 ; -to decide how different the rate determining steps are in the three reactions by comparing the activation energies e 0 B ; e 0 C\6 , and determined in [1] e 0 TH on the different samples; -to evaluate the differences between active site distribution in the case of the three reactions from the compensation of parameters of the Arrhenius equation (e 0 and k 0 ); -to calculate the bond energy values of H, C and S atoms with the catalyst surface (Q X,Cat-s ) from the e values, expressing the affinities of the different catalysts to interact with H, S and C in the reacting groups.…”