A comparative study of the catalytic performance of Co-Mo and Co(Ni)-W carbide catalysts in the hydrodenitrogenation (HDN) reaction of pyridine

In this contribution the HDN catalytic behaviour of Co-Mo carbide catalysts and Co(Ni)-W carbide catalysts is compared in order to establish a rational effect of cobalt (or nickel) over Mo and W carbide HDN catalysts. The bimetallic and trimetallic catalysts were characterized by using elemental analysis, X-ray diffraction (XRD), infrared spectroscopy, Raman spectroscopy, thermo-gravimetric analysis and measurements of BET specific surface area. The catalytic performance was evaluated in a continuous flow reactor using hydrodenitrogenation of pyridine as model reaction.The incorporation of cobalt onto the structure of Mo2C reached an optimal Co/Mo ratio of 0.43 (i.e. Co4Mo6Cx catalyst), whose HDN activity and stability was markedly higher than industrial catalysts (i.e. CoMoS/Al2O3 and NiMoS/Al2O3). Higher molar ratios facilitated the segregation of promoter. This was reflected in a poor catalytic stability not only on Co-Mo carbide catalysts, but also on the Co(Ni)-W carbide catalysts. The CoWCx bimetallic catalyst was more active in the steady state than Ni-containing catalysts. Two modes of pyridine adsorption may occur in the HDN reaction, the end-on mode appears to be the more favourable at low temperatures whereas the side-on mode is more favourable at higher temperatures. Further increasing reaction temperature over 400 °C leads to an increase in the hydrogenolysis reaction so more methane is produced, while the percentage of other hydrocarbon products decreased.

The incorporation of cobalt into the structure of Mo2C reached an optimal Co/Mo ratio of 0.43 (i.e. Co4Mo6Cx catalyst), whose HDN activity and stability was markedly higher than industrial catalysts (i.e. CoMoS/Al2O3 and NiMoS/Al2O3). Higher molar ratios facilitated the segregation of promoter. This was reflected in a poor catalytic stability not only on Co-Mo carbide catalysts, but also on the Co(Ni)-W carbide catalysts.Figure optionsDownload as PowerPoint slide