Preparation And Oxidation Desulfurization Performance Of Tungsten-molybdenum Doped Graphite Phase Carbon Nitride Composites

Many countries have strict environmental regulations that limit sulfur in fuel oil to less than 10 mg/L and even require the use of sulfur-free fuels.Therefore,in order to obtain ultra-low sulfur fuel,fuel deep desulfurization has become a worldwide environmental problem to be solved.In this paper,a series of composite catalysts were prepared by combining tungsten-molybdenum based compounds with graphite phase carbon nitride(g-C₃N₄).The prepared catalysts were characterized by XRD,BET,FT-IR,XPS,SEM and TEM.H₂O₂ was used as oxidant,acetonitrile as extraction agent.The desulfurization performance of thiophene catalyst was studied by using thiophene compound as model oil.A series of supported amphiphilic quaternary ammonium phosphotungstate（molybdenum）peroxate catalysts were prepared by precipitation method:CTAB-PW（x）/g-C₃N₄、CTAB-PMo（50%）/g-C₃N₄、TBAB-PW（50%）/g-C₃N₄、TBAB-PMo（50%）/g-C₃N_4,and the following results were obtained:（1）With the increase of the loading capacity of CTAB-PW,its desulfurization performance improves first and then decreases.The catalyst prepared with 50%loading capacity of CTAB-PW has the best desulfurization effect.（2）The optimal desulfurization conditions were as follows:CTAB-PW（50%）/g-C₃N₄ catalyst dosage 0.04 g,simulated oil dosage 10 m L,reaction temperature 60℃,O/S ratio 8:1,reaction time 2 h.Under these conditions,the removal rate of BT can reach 99.9%,and the desulfurization rates of DBT,4,6-DMBT and TP over CTAB-PW（50%）/g-C₃N₄ catalyst are 99.9%,98.9%and 57.4%,respectively.（3）It was found that combining phosphotungstic acid with quaternary ammonium salt CTAB and loading it on g-C₃N₄ could effectively inhibit the leaching of active phase phosphotungstic acid and effectively improve the regeneration performance of the catalyst.MoO₃（50%）/g-C₃N₄ composite catalysts with different MoO₃ doping amount were synthesized by roasting.The results are as follows:（1）With the increase of MoO₃ doping amount,the desulfurization performance of MoO₃（50%）/g-C₃N₄ catalyst prepared with 50%MoO₃ content has the best desulfurization effect;（2）The optimal desulfurization conditions were as follows:MoO₃（50%）/g-C₃N₄ catalyst dosage 0.06 g,simulated oil dosage 10 m L,acetonitrile dosage 1 m L,reaction temperature 70℃,O/S ratio 10:1,reaction time 90min.Under these conditions,the removal rate of BT can reach 99.9%,which is 13.7%higher than that of pure MoO₃,indicating that MoO₃ doped with g-C₃N₄ can significantly increase the desulfurization activity of MoO₃ catalyst.And MoO₃（50%）/g-C₃N₄ catalyst for DBT,4,6-DMBT and TP desulfurization rate reached more than 90%,showing excellent desulfurization performance.（3）MoO₃（50%）/g-C₃N₄ had good regeneration performance.After the catalyst was reused for 5 times,the BT desulfurization rate remained 95.5%,which was only 4.4%lower than that of the fresh catalyst.FT-IR characterization showed that the structure of the catalyst was not damaged.The W-MoO₃（x）/g-C₃N₄ composite catalysts with different W-MoO₃ doping amount were synthesized by roasting.The results are as follows:（1）With the increase of W-MoO₃doping amount,the desulfurization performance of the catalyst is improved first and then decreased.The catalyst prepared with 10%W-MoO₃ content has the best desulfurization effect.（2）The optimal desulfurization conditions are as follows:catalyst dosage 0.03 g,simulated oil dosage 10 m L,acetonitrile dosage 1 m L,reaction temperature 60℃,O/S ratio8:1,reaction time 30 min.Under these conditions,the removal rate of BT can reach 99.9%,which is 7.7%higher than that of pure W-MoO₃,indicating that doping W-MoO₃ with g-C₃N₄can significantly increase the desulfurization activity of W-MoO₃catalyst.The desulfurization rates of DBT,4,6-DMBT and TP over W-MoO₃（x）/g-C₃N₄ catalyst reached99.9%,showing excellent desulfurization performance.（3）W-MoO₃（x）/g-C₃N₄ has good regeneration performance.The BT desulfurization rate of W-MoO₃（x）/g-C₃N₄ catalyst remains 97.3%after repeated use of the catalyst for 5 times,which is only 2.6%lower than that of the fresh catalyst.The structure of the catalyst has not been destroyed by FT-IR characterization.