Sulfur exchange via HDS of thioaromatic compounds

The exchange of H2S formed in hydrodesulfurization of DBT with S-labelled surface sulfur of alumina supported CoMoOx has been studied by Cachet et a/. They foimd that catalyst sulfur was replaced by non-radioactive sulfur fi om DBT and released in H2 S. 

The Tokyo Group (Kabe and colleagues) has performed a high number of studies with S labelled thioaromatic compoimds, mostly DBT, on sulfided alumina supported MoOx, Co, CoMoOx, Ni and NiMoOx, and noble metals. 

Referred to in Sec. 2.3, the sulfur uptakes of the non-presulfided samples were determined from H2 S- S-DBT radioactivity balance at HDS of S-labelled DBT, by addition of a 1% decalin solution of this compound. However, it was observed that a substantial difference in the behaviour of presulfided and non-presulfided samples, the introduction of p S] DBT to presulfided samples, resulted in a rapidly approached steady state of DBT 

The fraction of Smob/Soat and the amounts of mobile sulfur for C0M0S2 were 8—43% and 2.8—7.5 x lO S atoms/mg respectively in the 533—673 K interval,similar to the values obtained with H2 S experiments. 

On alumina supported Pd and Pt, the Smob/Scat was 0.2 and 0.12 the amount of mobile sulfur was 3—3.9 x 10 S atoms/mg at 533K.I 1 According to the authors opinion, the difference between the molybdena based and the noble metal catalysts, is a consequence of the attachment of a part of sulfur to the alumina support of the noble metal catalysts. The data indicate that almost all sulfur accommodated on the noble metals was mobile, i.e., exchangeable and participated in the HDS reaction. This was different from the case with molybdena-based catalysts. This observation was confirmed recently that Smob/Pd(Pd- -Pt) ratio was 0.2, both for alumina supported Pd and Pd-Pt, irrespective of the H2S partial pressure and the amount of the total sulfur uptake. 

---