Preparation Of Ni₂P Hydrodesulfurization Catalyst

Ni₂P is a hydrodesulfurization catalyst with high activity and sulfur tolerance.However,compared with the traditional metal sulfide catalysts,the preparation conditions of Ni₂P catalyst are rather harsh.For example,high temperature,slow heating rate and large hydrogen flow rate are required when Ni₂P catalyst is prepared by TPR method.Therefore,optimizing the preparation conditions of the catalyst,increasing the dispersion of the active phase on the supported catalyst,and discussing the changes of phosphorus species during the preparation process are of great significance for the preparation of Ni₂P catalysts.In order to reduce the reduction temperature and avoid the influence of impurity ions?such as sodium,chlorine,etc?,bulk Ni₂P was prepared by low-temperature hydrogen plasma from oxide precursors with hypophosphorous acid as the phosphorus source.The effects of the rising rate of the generator voltage,the flow rate of reducing gas?H₂?,the final reduction voltage,and the reduction time on the formation of Ni₂P were investigated.The prepared catalysts were characterized by means of XRD,FT-IR and ICP-AES.The catalytic performance in HDS was evaluated with the decalin solution of dibenzothiophene?0.8 wt%?as a model fuel.It is shown that the hydrogen plasma reduction conditions are of vital importance in preparing Ni₂P catalyst when H₃PO₂ was used as the phosphorus source.Phosphorous-containing impurities,such as Ni₂P₄O₁₂·10H₂O,H₃PO₄,and Ni?PO₃?₂ appeared in Ni₂P under unfavorable reduction conditions,which inhibited the HDS activity of Ni₂P.The phosphorus-containing impurities can be partially washed by deionized water and the reaction activity can be slightly improved.The phosphorus-containing impurities can be mostly washed by using ammonia and the reaction activity can be obviously improved.Therefore,the phosphorus-containing impurities in the catalyst are important factor affecting the reaction.Selecting suitable preparation conditions to inhibit the formation of phosphorus-containing impurities can enhance the reaction performance.The supported Ni₂P/SiO₂ catalysts were prepared by introducing various organic additives?sorbitol,citric acid,tartaric acid,and ethylenediaminetetraacetic acid?,and sorbitol was determined to be the best organic additive.The Ni₂P/SiO₂ catalysts modified by sorbitol?Sorb-Ni₂P/SiO₂?were prepared by TPR method.Calcination atmosphere,gas flow rate,sorbitol content and Ni₂P loading were investigated.The Sorb-Ni₂P/SiO₂ catalysts were characterized by X-ray diffraction?XRD?and N₂ Adsorption-Desorption Isotherms,and the HDS activity of the catalysts were investigated.The experimental results showed that 100 mL/min of air,Sorb/Ni with a molar ratio of 1 and Ni₂P with a loading of 20%were the best preparation conditions.The performance of the catalyst prepared by PR and TPR method was evaluated under the optimal conditions.The HDS activity of the Sorb-Ni₂P/SiO₂ catalysts prepared by the TPR method is better than that of PR method under the optimal ratio.The reason is that Ni₂P can be prepared according to the stoichiometric ratio by PR method,whereas the molar ratio of P/Ni at 1 in this experiment leading to excess P and inefficient activity.