Publication

Abstract : A new family of bimetallic oxycarbide compounds MI–MII–O–C (MI=Mo, W; MII=V, Nb, Cr, Fe, Co, Ni) has been synthesized by carburizing bimetallic oxide precursors using a temperature-programmed method. The oxide precursors are prepared by conventional solid-state reaction between two appropriate monometallic oxides. The synthesis involves passing a 20 mol% {CH4} in {H2} mixture over the oxide precursors while raising the temperature at a linear rate of 8.3×10−2 K s−1 (5 K/min) to a final temperature (Tmax) which is held for a period of time (thold). The synthesis, chemisorption properties, and reactivation of the materials indicate that the compounds can be divided into two groups of different reducibility (high and low). Their surface activity and surface area are evaluated based on {CO} chemisorption and {N2} physisorption measurements. It is found that the {CO} number density correlates with the reducibility of the compounds. The catalysts were evaluated for hydroprocessing in a three-phase trickle-bed reactor operated at 3.1 {MPa} and 643 K. The feed was a model liquid mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The bimetallic oxycarbides had moderate activity for {HDN} of quinoline, with Nb–Mo–O–C showing higher {HDN} than a commercial sulfided Ni–Mo/Al2O3 catalyst tested at the same conditions. X-ray diffraction of the spent catalysts indicated that the oxycarbides of the early transition metals were tolerant of sulfur, while those involving the late transition metals showed bulk sulfide phases.