Design And Synthesis Of Strongly Acidic Coinage Metal-Pyrazolate Complexes And Their Application In Adsorptive Desulfurization

Adsorption desulfurization(ADS)is a promising technology for liquid fuel desulfurization.However,there are still some problems,such as low adsorption capacity of aromatic sulfur-containing compounds(HASC);the selectivity of HASC is poor in the presence of aromatic compounds.These problems hinder the practical application of ADS.In this paper,on the basis of previous work,a novel ligand,4-nitro-3,5-bis(trifluoromethyl)pyrazole,and its silver(Ⅰ)trinuclear complex(Ag3pz3)and copper(Ⅰ)trinuclear complex(Cu3pz3),were designed and synthesized.Ag3pz3 and Cu3pz3 are more acidic than the complexes we used before,and are expected to be used as molecular sorbents with better adsorption performance.Using iso-octane as the model oil,the adsorption desulfurization experimental results show that:at 25℃,the maximum adsorption capacities of M3pz3 for dibenzothiophene(DBT)and 4,6-dimethyldibenzothiophene(DMDBT)are 58.5 mg SDBT/g Ag3pz3,60.7 mg SDBT/g Cu3pz3,51.5 mg SDMDBT/g Ag3pz3 and 35.8 mg SDMDBT/g Cu3pz3.Ag3pz3 can reduce the S-content in iso-octane containing DBT or DMDBT from 100 mg S/L to～1 mg S/L after a static adsorption under the oil-to-sorbent ratio of 221 mL/g.However,the selectivity of Ag3pz3 for HASC is poor when the model oil contains aromatic compounds(such as 1 wt%naphthalene or 15%toluene(vtoluene:viso-octane=15:85)).In the presence of toluene,the percentage of S-removal of DBT/DMDBT over Ag3pz3 decreases from 99%to 56%and 49%,respectively;in the presence of naphthalene,the percentage of S-removal decreases from 99%to 12%and 16%,respectively.The performance of Cu3pz3 to adsorb DBT from toluene-containing model oil is less affected,and the percentage of S-removal can still reach 90%,which is much better than that of Ag3pz3 under the same conditions,and the percentage of S-removal of DMDBT over Cu3pz3 decreases from 64%to 40%when toluene-containing model oil is used instead of iso-octane.In the presence of naphthalene,the percentage of S-removal of DBT decreases from 90%to 36%,the desulfurization rate of DMDBT decreases from 64%to 17%.According to our experimental results,in the absence of competitive aromatic compounds,the adsorption performance of Ag3pz3 for DBT/DMDBT is better than that of Cu3pz3,but in the presence of toluene or naphthalene,the adsorption selectivity of Cu3pz3 for DBT is obviously better than that of Ag3pz3.In order to reveal the different adsorption behaviors of Ag3pz3 and Cu3pz3 under the same conditions,we obtained the crystal structure information of the adducts of Ag3pz3 and Cu3pz3 with DBT/DMDBT by X-ray single crystal diffraction,and carried out theoretical research on this basis.It was found that during the adsorption of DBT by Ag3pz3 and Cu3pz3,Cu3pz3 combines with DBT via a short Cu…S distance(2.5437(10)?),while Ag3pz3 failed to form a short Ag…S distance with DBT.This may be the reason why the adsorption selectivity of Cu3pz3 is better than that of Ag3pz3;due to the steric hindrance of methyl groups on the 4 and 6 positions of DMDBT,both Cu3pz3 and Ag3pz3 fail to form a shorter M…S distance with DMDBT.Based on the findings in this paper,we propose that the adsorption selectivity could be improved by strengthening the M…S interactions or/and weakening M…C interactions.