Oxidative desulfurization (ODS) of organosulfur compounds catalyzed by peroxo-metallate complexes of WOx–ZrO2: Thermochemical, structural, and reactivity indexes analyses

An experimental and theoretical study on the relationships between oxidative reactivity, thermochemical viability, and structural requirement of the activity sites in oxidative desulfurization (ODS) process has been performed. A series of aromatic sulfur compounds and peroxo-metallate complexes of WOx–ZrO2 with different structures have been studied. The models chosen for mimicking the catalyst correspond to surface densities of ∼7 W nm−2. The results indicate that the ODS takes place in two consecutive stages: (i) the formation of sulfoxide and (ii) the formation of sulfone. However, a detailed analysis suggests that these stages occur in two separated steps, (a) addition and (b) elimination, involving the formation of intermediate adducts and that the elimination of sulfoxide from the site surface is the rate-determining step. The results also reveal that the thermochemical feasibility of the studied reactions depends on both: the local structure of the WOx–ZrO2 surface and on the nature of the aromatic sulfur compound. It was found that the reactions involving dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (46DMDBT) are the most favored reactions, while the reaction of thiophene (Th) is the least favored. Therefore, highly substituted dibenzothiophenes are the most readily oxidized species, which is in agreement with experimental evidence. An explanation to the different reactivity shown by sulfur compounds, during ODS processes, is provided.

The experimental-theoretical study reveal that the oxidative desulfurization (ODS) process takes place in two stages, the formation of sulfoxide and the formation of sulfone and that each stage occur in two independent steps, addition (1a and 2a) and elimination (1b and 2b), involving the formation of intermediate adducts. The values of the Gibbs free energy of activation show that the barriers of the addition steps are significantly lower than those of the elimination steps, supporting the hypothesis that the elimination is the rate-determining step of the ODS process.Figure optionsDownload high-quality image (56 K)Download as PowerPoint slideHighlights
► Thermochemical viability of oxidative desulfurization (ODS) reactions.
► Surface peroxo-metallate complexes of WOx–ZrO2 were modeled.
► Oxidative reactivity of sulfur compounds was established.
► Reactivity indexes provide an explanation to the thermochemical feasibility.