Ni₂P/ZrO₂-SBA-15 Hydrodesulfurization Catalysts:Preparation,Characterization And Evaluation

Sulfur content in fuel has been restricted stringently according to environmental requirements.Currently,the sulfur is removed from fuel by the catalytic hydrodesulfurization?HDS?of sulfur-containing compounds.The commercial HDS catalystsnowadaysaretransitionmetalsulfidessupportedon alumina?CoMoS/?-Al₂O₃ and NiMoS/?-Al₂O₃?.The operation conditions of these catalysts are very hard when producing ultra-low sulfer fules.Transition metal phosphide has much more surface activity sites for catalytic hydrodesulfurization than sulfide catalysts.Therefore,the investigation of transition metal phosphide HDS catalysts has received great attention in recent years.In this paper,firstly,surface of SBA-15 molecular sieve was modified by ZrO₂ to prepare an excellent kind of support with large specific surface area and suitable chemical activity.The influences of different preparation conditions on the specific surface area,pore structure and crystal structure of the modified support were studied and the mechanism of the surface modification process was discussed.Secondly,Ni₂P/ZrO₂-SBA-15 catalysts with different Ni/P molar ratio,zirconium n-propoxide/SBA-15 mass ratio and Ni₂P mass fraction were synthesized to investigate their effects on the catalysts specific surface area,pore structure,crystal structure and their active phase dispersion conditions.Finally,the hydrodesulfurization performances of the prepared catalysts were evaluated under different temperatures in a high pressure micro-fixed-bed reactor using dibenzothiophene as feed stock.The results indicated that by reacting with hydroxyl on the surface of SBA-15,zirconium was incorporated in the form of[?-O-?₂Si?-O-Zr?₂]and/or[?-O-?₃Si-O-Zr],and the interplanar spacing of SBA-15 increased after this modification process.This modification process resulted in a decrease in the specific surface area,pore volume and pore size of SBA-15,but long-range orderly mesoporous structure of SBA-15was still kept intact.The introduction of the active phase Ni₂P showed a certain effect on the micropores and mesopores structures of the catalyst,and even destroyed its pore structures.During the preparation process,Ni₂P phase was formed when the Ni/P molar ratio is 1/2;ZrO₂ incorporation into the SBA-15 was beneficial for the formation and dispersion of Ni₂P.The tetragonal ZrO₂ phase was formed gradually with ZrO₂ content increasing.Besides Ni₂P,another kind of active phase,ZrP,was formed with an appropriate content of zirconium and nickel phosphide.The most preferable catalysts preparation conditions are:Ni/P molar ratio is 1/2;zirconium n-propoxide/SBA-15 mass ratio is 1.5;Ni₂P mass fraction is 20%.It was observed that with the temperature of 280°C,the pressure of 3.0 MPa,the WHSV of6.5 h^-1 and the H₂ to oil ratio of 450,the prepared catalyst showed the highest DBT conversion,which was 86.6%,almost 35%percent higher than Ni₂P/SBA-15 catalyst.Therefore,the transition metal phosphide catalyst is expected to be further developed in the field of fuel hydrodesulfurization.