Study On The Controllable Synthesis And Hydrodechlorination Performance Of Molybdenum Phosphide

Organic chlorides as cleaning agent and solvent have always played an indelible role in the development of chemistry.However,organic chloride causes harm to the human body and the environment,so the problem on degrading chloride is particularly urgent.Among the most studied catalysts for dichlorination reactions,transition metal phosphides（TMPs）are valued because of their electrical conductivity and chemical stability.Mo P,as an important one of TMPs,has also received great attention.Mo P has single crystal structure and unstable lattice structure,which makes more potential coordination unsaturation sites.But the current application of Mo P as a catalyst still has some problems.Mo P is prone to agglomerate due to high-temperature preparation conditions,resulting in the poor catalytic activity.Secondly,the structure-activity relationship between active sites and the catalytic performance is still rarely researched,which makes it difficult to controllably synthesize highly active Mo P.Here,the activity of Mo P is designed to improve through morphology modification and element doping,and intrinsic factors affecting the activity and stability of Mo P are also explored from the perspective of valence bond changes,which provides useful reference for the subsequent design of highly active Mo P.The main contents of this thesis are as follows:1.Hollow tubular Mo P@C was synthesized by choosing absorbent cotton with the special tubular morphology as a template.Compared with unmodified Mo P,Mo P@C has a larger specific surface area and a higher degree of dispersion of active components,so that Mo P@C has higher catalytic activity for HDC of trichloroethylene.Besides,by increasing the amount of absorbent cotton,the morphology of Mo P@C showed a trend of changing from blocky accumulation to hollow tube,and finally to a crimped ribbon,while the activity of catalysts correspondingly increased at first and then drop.When the addition of absorbent cotton is 2.5 g,the best activity of Mo P@C-14.1 is 47.18%,which is nearly twice as high as 24.98%of unmodified Mo P.Therefore,absorbent cotton acted as a template is an effective way to control the morphology of TMPs.This method is simple to operate,and raw materials are easy to obtain,which can provide a fresh insight for preparing high-activity TMPs with different morphologies.2.By investigating the important role of oxygen in the Mo P catalyst,it is proposed that the Mo-P-O bond in Mo P,different from PO₄^3-and molybdenum oxide,is the key to the activity of the hydrodechlorination reaction.The structure and performance changes of Mo P before and after the reaction was compared at different temperatures,and found that the catalytic process of Mo P hydrodechlorination was accompanied by the consumption of Mo-P-O bond.Because of the stronger electronegativity and different electronic structure of O,dangling bonds appear in Mo P,leading to the instability of the Mo P structure.Therefore,strong oxidation method is adopted for increasing the content of Mo-P-O bonds to restore the activity of deactivated Mo P.The activity of Mo P/H₂O₂ at 500°C recovered to 19.92%,which was only slightly lower than that of the original Mo P（24.98%）.After the above oxidation treatment was repeated three times,the catalytic activity restored to 10.46%,which was still better than that of Mo P after the first temperature cycle.It is simple and feasible to use H₂O₂treatment for increasing the content of Mo-P-O bonds and realize the recovery of catalytic performance,which has reference significance for improving the catalytic performance and cycle stability of TMPs.3.The method of synergistic modification of EDTA and glucose is used to prepare Mo P/x EG co-doped with C and O.Compared with unmodified Mo P,the doping of carbon and oxygen in Mo P/x EG speeds up the charge transfer and supplies more exposed active sites in the catalytic process.Besides,Mo P is highly dispersed on the carbon matrix,which increases the specific surface area of the catalyst and facilitates the adsorption of reactants on the catalyst surface,thereby effectively improving the catalytic activity of the modified Mo P/x EG.In case of changing molar ratio of Mo P and surface modifier,the best activity of Mo P/0.5EG reached 57.80%,which is 2.3times higher than the performance of Mo P catalyst.