| Rencently,there is a tendency of the supply of heavier crude oil with decreasing quality.At the same time,the rigorous environmental regulations require the much lower sulfur content of petroleum products.Therefore,the development of high-performance hydrodesulfurization(HDS)catalysts with novel active phases becomes urgent,among which the Ni2P catalysts become a hot topic because of its excellent catalytic performance.However,the high temperature needed leads to the agglomeration of Ni2P particles,and decrease the catalytic performance.The preparation temperation can be decreased greatly by using hypophosphite with lower oxidation number,which is benefical for the performance of the catalyst.Furthmore,the HDS activity of Ni2P can be improved by the introduction of promoters.In this paper,NH4H2PO2 was utilized as phorsphrous source,and MoS2 was added to the Ni2P catalysts.The HDS performance of the catalyst was studied by using hydrodesulfurization(DBT)as a model compound of sulfur.Firstly,the preparation of Ni2P+MoS2 mixture was investigated using two paths:Ni(NO3)2+(NH4)6Mo7O24 and Ni(CH3COO)2+(NH4)2MoS4 respectively.The results show that Ni(NO3)2+(NH4)6Mo7O24was calcined,followed by sulfidation to obtain Ni9S8+MoS2.Then the sulfides were phosphided with NH4H2PO2(P/Ni=3)in N2;Ni(CH3COO)2+(NH4)2MoS4can be directly phosphided in N2 to obtain a mixture of Ni2P+MoS2.Ni O+MoO3could be phosphided with NH4H2PO2 in H2S/H2 to obtain Ni2P+MoS2.With the increase of the sulfuration time,more pyrophosphoric acid and ammonium metaphosphate can be observed to.The Ni2P-MoS2/Al2O3 catalysts(the loading of Ni2P is higher than that of MoS2)were prepared on the basis of the optimized conditions of the bulk mixtures.The reactivity of the catalyst was investigated and the catalysts were characterized.The synergistic effect of MoS2and Ni2P in the reaction was investigated.The results show that Ni2P-MoS2/Al2O3 catalysts prepared by co-impregnation of Ni(NO3)2+(NH4)6Mo7O24 on Al2O3 show the highest activity,which was much higher than that of Ni2P/Al2O3 and MoS2/Al2O3 catalysts with same loading,also higher than the Ni2P-MoS2/Al2O3 catalyst prepared by Ni(CH3COO)2 and(NH4)2MoS4.Different impregnation methods have an effect on catalyst particle size,surface element distribution,interaction between metal particles and carriers,and dispersion of Ni2P and MoS2.The selectivity of catalyst was mainly direct desulfurization.For the Ni2P-MoS2/Al2O3catalyst,different impregnation methods had influence on particle size of the catalysts,surface element distribution,interaction between metal particles and support,and dispersion of Ni2P and MoS2.When Ni O+MoO3 was phosphided with NH4H2PO2 in H2S/H2,it needed to react at 400°C for 1 h after reacted at 300°C,and then MoO3 was be completely sulfided.The reactivity of the obtained catalyst was lower than those of catalysts with longer reaction time at 400°C.The MoS2-Ni2P/Al2O3 catalyst(the loading of MoS2 was higher than that of Ni2P)was prepared by co-impregnation with Ni(NO3)2+(NH4)6Mo7O24.The activity and structural characteristics were studied and compared with the sulfided Mo-Ni-S/Al2O3 catalyst.The results show that the HDS conversion of MoS2-Ni2P/Al2O3 was 95.9%at 330°C?3.0 MPa,And the optimum P/Ni was 3.The activity of the catalyst was lower than that of Mo-Ni-S/Al2O3,mainly because the number of stacking layers of the MoS2 was fewer and the length of the crystal plate was shorter after phosphation.When MoO3-Ni O/Al2O3 was phosphated with NH4H2PO2(P/Ni=3)directly in H2S/H2,the catalyst that reacted at 400°C for 2 h had higher specific surface area,and the proporation of Mo4+and Ni?+is relatively higher.The HDS conversion of it was 97.4%. |
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