Controllable Synthesis And The Hydrodechlorination Performance Of Nickel Phosphides

Transition metal phosphides?TMPs?,which were also named as“quasi platinum catalyst”,have attracted much attention because of their particular structure and excellent catalytic activities comparing to noble metal catalysts.Among these TMPs,nickel phosphide has attracted extensive attention of researchers because it is not only the most active mono-metallic phosphide,but also existing in a variety of phases(such as Ni₃P,Ni₂P,Ni₁₂P₅,Ni₅P₄,NiP₂,NiP₃).As the most common phases,Ni₂P can transfer to Ni₁₂P₅ under certain conditions.Different crystalline phase would exhibit different catalytic activity,which was due to different phase would show different morphology and expose different crystal facets.Specific surface area would be greatly affected by the morphology,resulting in different catalytic activities;reaction rate would be affected by the difference of crystal facets,which means that different facets of crystal exhibit different catalytic performance.The transition metal phosphides catalysts for hydrodechlorination degradation of trichloroethylene?TCE?show a good application prospect.In order to enhance the catalytic activity and stability of TCE catalysts,the controllable synthesis of crystal phase,facets and morphology are to be particularly important,especially the controllable synthesis of catalyst that exposes high active crystal facets.In the thesis,nickel phosphide was synthesized via a facile hydrothermal process with red phosphorous as the phosphorous source.Firstly,the crystalline phase and the degree of corresponding exposed crystal facets were adjusted by changing the amount of additives in the hydrothermal system;secondly different structure of Ni-MOFs were synthesized by selected certain carboxylic acid ligands with different amount of carboxyl in order to prepared different morphology of nickel phosphide.Then the catalysts were characterized by X-ray diffraction?XRD?,Scanning electron microscope?SEM?,Transimission electron microscopy?TEM?and BET to explore the formation mechanism of different crystalline phase and morphology.Finally,the above nickel phosphide catalysts were applied to hydrodechlorination of TCE,and explored the relationship between crystalline phase,crystal facets,morphology and catalytic activity.The detailed conclusions were as follows:1.Hexagonal Ni₂P can transfer to tetragonal Ni₁₂P₅ via adjusting the amount of additives?urea/NaF/NH₄F?in the hydrothermal system,and at the same time,the degree of corresponding exposed crystal facets were changed.There were electronegativity anions or groups in the additives,which would compete with P to adhere to the surface of Ni species,thus decreasing the amount of P doping into Ni crystal lattice and decreasing the content of P in the final products of nickel phosphide,eventually inducing to formation of a new phase.Meanwhile,the growth of certain crystal facets would be inhibited or promoted to a different extent by the additives,resulting in the changing of exposed crystal facets.2.Due to the existence of variety coordination forms of carboxyl,when there were different amount of carboxyl in the carboxyl acid,different structure of Ni-MOFs could be synthesized.Compared to the prepared Ni₁₂P₅ via common hydrothermal method,a series of different morphology of tetragonal Ni₁₂P₅ could be prepared with Ni-MOFs as precursor under hydrothermal condition,and which would display well thermal stability.BET surface area of catalysts were promoted resulting in the promotion of catalytic activity,and the catalysts exhibited good stability under high temperature reaction condition.