Study On Preparation Methods Of Transition Metal (Mo,Ni And Co) Phosphide

Transition metal phosphides are a class of interstitial compounds.Because of its similar catalytic properties with noble metals and potential applications in many fields,it has attracted wide attention,such as magnetism,electronics,photonics,catalysis and so on.Metal phosphides have been used as excellent catalysts for various reactions including hydrogenation and hydrotreating,NO reduction,N₂H₄ decomposition and hydrogen evolution reaction and so on.Since the discovery that the catalytic performance of transition metal phosphides depends on the size of their particles,there has been a great interest in nano-scale metal phosphides,so the preparation methods of transition metal phosphides have attracted wide attention.Therefore,this study mainly studied two methods for synthesizing transition metal phosphides.The first method is the dimethyl ether rapid heating reduction method?RHR-DME?.Unlike the conventional TPR-H₂ method,the reducing agent used for RHR-DME is dimethyl ether?DME?instead of H₂.The second method is an improved H₂ reduction method to synthesize metal phosphides,in which the precursor of metal phosphides is prepared by simple mechanical mixing of metal oxides?MO_s?and P₂O₅.The main research results are as follows:Transition metal phosphides Ni₂P?Co₂P?MoP were prepared by rapid heating reduction with dimethyl ether?DME?as reducing agent.The main components of the gas phase products in this reaction are H₂,CO and CH₄,followed by a small amount of CO₂,but does not contain H₂O.Based on the characterization results of XRD and MS,the formation mechanism of phosphide was proposed.However,the whole synthesis process can not be simply regarded as the reduction of metal oxide precursors and the decomposition of dimethyl ether.The composition of the product and its content are also affected by other catalytic reactions.It is noteworthy that compared with the traditional method?TPR-H₂?,this method uses a higher heating rate,shortens the reaction time,and can prepare metal phosphide nanoparticles with good dispersion.Metal phosphides Ni₂P,Co₂P and MoP were synthesized by H₂ reduction method using a mixture of metal oxides?MO_s?and phosphorus pentoxide?P₂O₅?after simple mechanical grinding as a precursor.In addition,this is the first time that the common solid P₂O₅ is used as a P source for the preparation of metal phosphides.The route of preparation is not the direct conversion from amorphous phase to phosphide,but the conversion from MO_s/P₂O₅ precursor to phosphide is participated by different specific intermediates.According to the results of XRD,XPS,SEM,TEM and other analysis,the formation of phosphide is basically determined.