Effect of Citric Acid on the Hydrodesulfurization Performance of Ni<sub>2</sub>P/TiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> Catalyst

Abstract

A TiO 2 -Al 2 O 3 complex support was prepared by the sol-gel method.Nickel phosphide catalyst, Ni 2 P/TiO 2 -Al 2 O 3 ,with citric acid(CA)as a chelating agent,was prepared by impregnation.The catalyst was characterized by X-ray diffraction(XRD),BET specific surface area measurements,H 2 -temperature programmed reduction(TPR)and temperature programmed oxidation(TPO),and X-ray photoelectron spectroscopy(XPS).The effects of the molar ratio of CA to Ni on catalyst activity for hydrodesulfurization (HDS)of dibenzothiophene(DBT)were studied.Addition of an appropriate amount of CA into the catalyst can change the pores of the Ni 2 P/TiO 2 -Al 2 O 3 catalyst,increasing the surface area.The specific surface area reached 126.75 m 2 ·g -1 for n(CA)/n(Ni)of 2/1,an improvement of 57.05 m 2 ·g -1 compared with the catalyst without CA.Regulating n(CA)/n(Ni)can improve the distribution of the active phase and change the active phase species.Addition of CA decreased the temperature required for reduction of nickel and the phosphorus precursor,as well as promoting the formation of the active phase.CA can limit the deposition of carbon on the catalyst surface to some extent,improving its stability.A molar ratio of n(CA)/n(Ni)of 2/1 was found to be optimal for the catalytic activity of the Ni 2 P/TiO 2 -Al 2 O 3 catalyst prepared with CA as a chelating agent.At a reaction temperature of 360°C,pressure of 3.0 MPa,hydrogen/oil ratio of 500(V/V), and liquid hourly space velocity of 2.0 h -1 ,the HDS conversion of DBT was 99.5%,which can reduce the sulfur content of a model oil from 2%(w)to 0.01%(w).