Preparation And Characterization Of Unsupported Nickel Phosphide Catalyst And Its Hydrodesulfurization Performance

In this paper,a series of iron（Fe）modified unsupported nickel phosphide were successfully prepared by temperature programmed reduction（TPR）method（xFe-Ni₂P,x is the ratio of the amount of Fe to Ni₂P）.The TPR method was improved by using nickel citrate as a nickel source,and a highly dispersed unsupported nickel phosphide catalyst was obtained by reduction at500°C（Ni₂P（x）-L,x is the reduction temperature）,and Fe modified unsupported nickel phosphide were prepared by using nickel citrate as a nickel source（0.03Fe-Ni₂P（500）-L）.At the same time,the catalysts were characterized by XRD,BET,CO uptake,XPS and TEM.Using dibenzothiophene（DBT）as the model sulfide,the effect of Fe content on the hydrodesulfurization activity of Ni₂P and HDS reaction conditions on desulfurization was investigated.The results of Fe modified catalyst showed that the nickel phosphide species in the catalyst sample are mainly in the form of Ni₂P.With the increase of Fe content,the size of catalyst was decrease,and the specific surface area and pore volume were increasing gradually.The amount of CO adsorption increased first and then decreased with the change of Fe content.The results of HDS activity evaluation showed that the addition of Fe can increase the HDS activity of Ni₂P catalyst.With increasing Fe content,HDS activity increased first and then decreased.Under the conditions of temperature 340℃,pressure 3MPa,mass space velocity 3h^-1,hydrogen/oil ratio600v/v,the DBT conversion of Ni₂P-Fe_0.03catalyst was the highest,reaching 89.2%,which was27.1%higher than unmodified Ni₂P catalyst.The selectivity of CHB was improved with increasing Fe content.The reaction of DBT via the HYD pathway was promoted by Fe.For preparing unsupported catalysts by using nickel citrate as the source of nickel,results indicated that the reduction temperature of catalysts prepared by nickel citrate was 500°C,which was 150°C lower than TPR method.The nickel citrate can greatly increase surface area of Ni₂P catalyst,and promote formation of much smaller and highly dispersed uniform Ni₂P particles,exposure of more active Ni sites on the surface of Ni₂P（x）-L.The catalyst which reduced at 500°C exhibited the greatest HDS activity.Under the conditions of temperature340°C,pressure 3MPa,mass space velocity 3h^-1,hydrogen/oil ratio 600v/v,the DBT conversion reached 95.6%,this is an increase of 33.5%when compared to that of the Ni₂P.The results of Fe modified catalyst which was prepared by using nickel citrate showed that the catalyst has the advantages of x Fe-Ni₂P and Ni₂P（x）-L catalysts,has a low reduction temperature and a high specific surface area,better dispersibility and smaller Ni₂P crystallite size.Under the conditions of temperature 340°C,pressure 3MPa,mass space velocity 3h^-1,hydrogen/oil ratio 600v/v,the DBT conversion reached 97.0%,this is an increase of 34.9%when compared to that of the Ni₂P.The DBT conversions of catalysts exhibited in a certain sequence:0.03Fe-Ni₂P（500）-L>Ni₂P（500）-L>0.03Fe-Ni₂P>Ni₂P-C.