Ultrasound assisted synthesis and physicochemical characterizations of fluorine-modified CoMo/Al2O3 nanocatalysts used for hydrodesulfurization of thiophene.

A series of CoMo/F-Al2O3 nanocatalysts with different fluorine loadings of 0, 0.4, 0.8 and 1 wt% were successfully synthesized by a sonochemical method and used for catalytic hydrodesulfurization (HDS) of thiophene. The nanocatalysts were characterized with X-ray diffraction analysis (XRD), Field Emission Scanning Electron Microscopy (FESEM), BET nitrogen adsorption Brunauer-Emmett-Teller (BET) analysis, Fourier Transform Infrared Spectroscopy (FTIR) and temperature programmed desorption of ammonia (TPD-NH3) techniques. The XRD results showed a high dispersion of the molybdenum species on the γ-Al2O3 support due to the application of sonochemical method along with fluorine addition. The CoMo/F-Al2O3 nanocatalysts had a particle size less than 100 nm. The specific surface area of the samples was slightly decreased with increasing the fluorine content. The FTIR results confirmed that with the increase of fluorine amount in the CoMo/Al2O3 nanocatalysts, it would generate more active sites. Moreover, the TPD results showed that the fluorinated nanocatalysts had higher acidity than the promoter-free nanocatalysts, because of the formation of new strong acid sites on the γ-Al2O3 support by the promoter. The catalytic activity for thiophene HDS reaction was investigated in a stirred slurry-tank reactor in the atmospheric pressure to determine the effect of fluorine amount on the nanocatalyst performance. The results of thiophene HDS reaction showed that the fluorinated nanocatalysts were more active than fluorine-free nanocatalysts and consequently, they were able to remove nearly 100% of thiophene in the initial solution. Furthermore, the nanocatalyst with the fluorine content of 0.8 wt% had the highest activity in HDS of thiophene. However, further addition of fluorine led to decrease in catalytic activity which could be attributed to the agglomerated particles formed on the nanocatalyst surface.