Introduction
Reducing the presence of naphthenic molecules through selective ring-opening (RO) is crucial in enhancing low-value crude oil quality. Traditionally, catalysts like iridium or platinum, supported on various aluminosilicates, have been used for this purpose. Although they exhibit decent RO capabilities, they are also highly susceptible to sulfur in the feed, showing a severe decrease in activity at sulfur levels as low as 20 ppm. Recently, transition metal sulfides (TMS) have emerged as a viable alternative, as they not only show high selectivity towards RO products without the need for noble metals but also exhibit a high tolerance towards typical catalyst poisons. In this study, we investigated supported TMS and the influence of metal concentration, reaction conditions, and the effect of various poisons on their selectivity towards RO products.

A series of supported catalysts containing nickel, tungsten, and molybdenum were prepared by impregnating SiO₂ using an aqueous solution of the respective metals. Reactions were performed in a trickle bed reactor, pressurized to 160 bar using H₂.

Results and Discussion
Our findings underscore the significance of equimolar (1.3 mmol_Metal*g_catalyst^-1) amounts of Ni, W, and Mo as the ideal ratio for supported TMS. Any deviation from these concentrations resulted in a noticeable reduction in activity. However, our investigation reveals that the type of active site remains consistent across different metal loadings, with variations observed only in the concentration of these active sites.

Our experiments clearly demonstrate the robustness of the catalyst. It is evident that an initial (skeletal) isomerization step is necessary, only then followed by a secondary ring-opening reaction and subsequent cracking to ≤C₉ units. Elevated pressures of >150 bar H₂ effectively minimize the formation of dehydrogenated products. Notably, the catalyst's activity and selectivity were barely affected by the presence of sulfur or nitrogen-containing compounds in the feed, highlighting its potential for practical applications.

<b>A:</b> Decalin consumption rate vs. molar amount of respective metals (○–Ni, △–W, x–Mo); <b>B:</b> Selectivity vs. molar amount of respective metals at constant conversions.

A: Decalin consumption rate vs. molar amount of respective metals (○–Ni, △–W, x–Mo); B: Selectivity vs. molar amount of respective metals at constant conversions.

Rachit Khare

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