Potassium effect in K-Ni(Co)PW/Al2O3 catalysts for selective hydrotreating of model FCC gasoline

•Using K led to the simultaneous decrease of Ni(Co)WS and rise of Ni(Co)Sx.•K adding poisoned the active sites and declined selectivity of Ni(Co)PW/Al2O3.•Modified catalysts can be ranged on the activity KWS < KNiWS << CoSx+KWS.•Increase of HDS/HYDO selectivity is followed by a decrease of HDS conversion.•The relevance of modifying catalyst with K strongly depends on a S content in feed.

Ni(Co)-PW/Al2O3 catalysts both unmodified and modified with potassium were synthesized with the use of H3PW12O40, CoCO3 or NiCO3, KOH and citric acid. The catalysts were characterized by the techniques such as low-temperature N2 adsorption, temperature-programmed reduction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The prepared samples were tested in hydrotreating of model FCC gasoline that contained 1000 ppm of sulfur from thiophene and 36 wt.% of n-hexene-1 as a representative olefinic compound. The modification with an alkali metal influenced both the characteristics of the catalyst active phase and catalytic properties of (K)-Ni(Co)-PW/Al2O3 samples. The incorporation of potassium led to some l growth of the linear size of active phase crystallites, to a decrease of reactivity and of the number of active sites, to a strong decrease of CoWS and NiWS particle amounts with a simultaneous rise of separate CoSx and NiSx. The potassium addition also induced a drastic drop of hydrodesulfurization (HDS) and hydrogenation (HYDO) activity with a HDS/HYDO selectivity decrease for Ni- and Co-promoted systems and with a significant increase of the selectivity factor for unpromoted PW/Al2O3. The Ni-promoted catalyst proved to be more sensitive to the potassium modification than the Co-promoted one. So, the modified catalysts can be ranged by activity as follows: KWS < KNiWS « CoSx + KWS. A key factor for selecting a catalyst was shown to be the chemical composition of FCC gasoline: feeds with a high sulfur amount required NiWS systems, whereas low sulfur feeds with a great amount of olefins should be hydrotreated with KCoMoS formulations.

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