Comparative study of MWCNT and alumina supported CoMo hydrotreating catalysts prepared with citric acid as chelating agent

Multi-walled carbon nanotubes (MWCNT) and alumina supported C.M. hydrotreating catalysts prepared with citric acid as a chelating agent (CoMoS/MWCNT-citr and CoMoS/Al2O3-citr respectively) were studied. MWCNT supported catalyst prepared without chelating agent (CoMoS/MWCNT) was also investigated. The addition of citric acid in MWCNT supported catalyst decreases the average slab length of MoS2 from 4.2 to 3.0 nm without increasing the stacking, while the differences in sulfidation degree and MoS2 promotion by cobalt are not observed. The activity of MWCNT-based catalyst in dibenzothiophene hydrodesulfurization (HDS) increases with the addition of citric acid due to improved dispersion of sulfide component. The activity in naphthalene hydrogenation does not change. The results of comparative study of MWCNT and Al2O3 supported catalysts prepared with citric acid show that the catalysts have rather similar morphology of sulfide phase: average slab length of about 3 nm and average stacking number of 1.6-1.7. At the same time, in MWCNT-based catalyst, active metals are sulfided more easily and CoMoS phase is formed at higher extent due to weaker metal-support interaction. CoMoS/MWCNT and CoMoS/Al2O3-citr catalysts are both highly active in HDS and demonstrate similar conversion of dibenzothiophene. The highest HDS activity of CoMo/MWCNT-citr catalyst is attributed to the beneficial effect that is provided by the combined use of carbon support (higher sulfidation degree and higher CoMoS phase content) and citric acid (improved dispersion of sulfide component).