The Study Of Benzene Hydrogenation Over Nickel Catalysts

In this paper, several Ni catalysts such as carbon-encapsulated nickel nanoparticle and supported Ni on Hβ, NaY, NaY-γ-Al2O3, HY-γ-Al2O3, USY-γ-Al2O3 andγ-Al2O3 were prepared, their activity for the hydrogenation of benzene were studied. Effects of preparation methods and conditions on the structure, dispersion of Ni, reduction properties and their relationship to the hydrogenation activity were also investigated by use of XRD, TPR, IR, TEM, NH3-TPD and TG-DTA techniques. It is found from experimental results that the carbon-encapsulated nickel nanoparticle catalyst has similar activity for hydrogenation of benzene as compared to Ni/γ-Al2O3. The existance of coated carbon has an effect of prohibiting the aggregation of nickel nanoparticle under high temperature hydrogen, the carbon-encapsulated nickel nanoparticle catalyst has better anti-aggregation ability over Ni/γ-Al2O3. Nickel nanoparticles disperse in carbon with an average size of 10nm～60nm. It is also found that the dispersion of Ni on Ni/Hβand Ni/NaY catalysts is poor, therefore, their activity for benzene hydrogenation is much lower than Ni/γ-Al2O3. The site of B acid had a negative effect on the activity of benzene hydrogenation, thus, Ni catalysts supported on NaY-γ-Al2O3, HY-γ-Al2O3 and USY-γ-Al2O3 carriers have lower activity for benzene hydrogenation as compared with Ni/γ-Al2O3. Theγ-Al2O3 supported Ni catalysts were characterized by in-situ XRD as well as BET, TPR and TG-DTA techniques. The effect of Ni content, precursor of Ni,method of activation,calcination and reduction conditions on the activity of catalysts for benzene hydrogenation were investigated.It was showed that the most suited NiO content is 25%～30%.When Ni(NO3)?6H2O was used as precursor,the catalyst possesses the highest catalytic activity. The activity of catalyst was also affected by activation methods. The activity of catalyst was higher when the direct reduction method was used than the calcination-reduction method. The optimized preparation conditions of catalysts are as follows: calcination temperature 450℃~500℃,reduction temperature 400℃,reduction time 6 hours.