| In this paper, hydrodesulfurization (HDS) catalytic performance of transition metal phosphide, cobalt phosphide, was studied. The HDS catalytic activity, selectivity, stability, reaction paths of cobalt phosphide were evaluated in a fixed bed with dibenzothiophene (DBT) as the model compound. The effects of Co/P ratio, passivation methods, preparation methods, reducing voltage, loading of supported catalyst on the HDS catalytic performance were investigated. At the same time, the crystal structure of cobalt phosphide and the adsorption behavior of H2 on the catalyst surface were also studied by means of density functional theory (DFT). The main contents are as follows:(1) Bulk cobalt-phosphide catalyst was synthesized by H2 plasma reduction and evaluated in a fixed bed with dibenzothiophene (DBT) as the model compound. The effects of Co/P ratio on the HDS catalytic performance were investigated. The highest HDS activity was obtained when Co/P=1.On this basis, the effects of H2S passivation and O2 passivation, temperature programmed reduction (TPR) and plasma reduction (PR) on the HDS catalytic performance were investigated. The results show that, the HDS activity of CoP catalyst with H2S passivation is higher than that with O2 passivation. The catalyst prepared by hydrogen plasma reduction performed a higher HDS activity than prepared by Temperature programmed reduction (TPR). The catalysts synthesized from different methods have little difference in selectivity and stability. Meanwhile, The HDS activity, selectivity, reaction paths and stability of CoP and Ni2P were compared. The experimental results show that, the HDS catalytic activity of CoP is higher than Ni2P. The CoP catalyst focuses on hydrodesulfurization reaction path, while Ni2P catalyst based on direct desulfurization route, both maintains a high stability.(2) Supported cobalt-phosphate catalyst was synthesized by H2 plasma reduction with SiO2 as the catalyst carrier. The HDS catalyst activity, selectivity, reaction paths of SiO2 supported cobalt phosphide were evaluated in a fixed bed with dibenzothiophene (DBT) as the model compound. The effects of Co/P ratio, reducing voltage and the loading of the SiO2 supported cobalt phosphide on the HDS catalytic performance were investigated. The results show that, the loading of 25% of the highest activity CoP/SiO2 HDS. The reaction path of HDS on SiO2 supported cobalt-phosphate, CoP/SiO2, mainly by HYD.(3) The CoP catalysts containing Ru, Ni were synthesized by means of non-equilibrium hydrogen plasma reduction, with RuCl3·3H2O as the Ru source, Ni (NO3)2·6H2O as the Ni source. SEM, XRD characterization indicated that, the CoP catalysts were synthesized at a lower voltage by adding Ru promoter. The HDS reaction of DBT over these CoP catalysts was performed in fixed bed reactor to evaluate their catalytic activity. The results show that, the addition of Ru and Ni can significantly improve the hydrodesulfurization (HDS) activity of CoP catalyst. The best incorporation rate of Ru is 0.1%, the Ni ratio is 5%; the incorporation of Ru improves the hydrogenation ability of CoP catalyst, and the Ni is favor to the directdesulfurization (DDS) reaction path.(4) The crystal structure, electronic structure, surface structure of cobalt phosphide and the adsorption configuration and energies of H2 on the catalyst surface were calculated and compared with experimental results using density functional theory (DFT), by means of CASTEP. The results show that, the crystal facet accounted for the largest proportion of the catalyst surface of cobalt phosphide is Co2P{101}, CoP{101}, CoP2{011}, CoP3{110}, respectively. The adsorption center of H2 on the catalyst surface is the metal Co atoms. The higher HDS activity of CoP may be associated with a higher adsorption ability of H2 and relatively low adsorption barrier. The low HDS catalytic activity of Co2P may be due to the larger adsorption energy barrier which hinders the hydrogen contact with the reactants on the catalyst surface. |
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