Regulation Of Palladium Electronic Properties In Bimetallic Phosphide And Its Catalytic Performance In Selective Reduction Of Nitrobenzene

Halogenated aromatic amines are widely used.They are a relatively basic chemical raw material,as well as an intermediate for chemical synthesis.They also play an important role in the fields of dyes,chemical additives,medicines,etc.,and become an indispensable part.In fine chemicals,halogenated aromatic amines are mainly prepared by reducing the corresponding halogenated nitrobenzene.The current mainstream reduction method in China is still the iron powder and sodium sulfide reduction method.However,in the above method,for every ton of product produced,there will be dozens or even hundreds of equivalents of toxic waste water and sludge which are difficult to handle,which seriously damages the ecological environment and therefore urgently needs to develop a clean and efficient production process.Catalytic reduction of nitro group to amine group by catalyst is a better choice,but this method has the problem of hydrodehalogenation,and the yield is not high,and there are many by-products.There are two main methods for preventing hydrodehalogenation.Adding a dehalogenation inhibitor or poisoning the catalyst,but adding a dehalogenation inhibitor will cause secondary pollution to the final product,increase the cost of separation and purification of the product,and the poisoning catalyst This will greatly reduce the activity of the catalyst and increase the cost.Therefore,it has become crucial to seek a good method to improve the performance of the catalyst and to improve the hydrodehalogenation of the catalyst without significantly reducing the activity and stability of the hydrogenation catalyst.The electronic properties of transition metals play an important role in the catalytic reaction,and electron transfer usually occurs on coordination or covalent bonds.The metal phosphide?M-P?material contains M-P covalent bonds and has been extensively studied in heterogeneous catalysis.They are usually co-reduced from a metal precursor and phosphine or hydrogen phosphate in a pot.The interaction of precious metals with metalloid elements makes metal electrons deficient,improving subsurface chemistry,atomic separation,and energy barriers for metal hydrides.Therefore,M-P nanomaterials have been used as highly efficient heterogeneous hydrogenation catalysts.M-P prepared using phosphine or hydrogen phosphate usually contains a lower phosphorus content,which makes the number of internal M-P bonds insufficient,so that the electronic valence of the metal can be effectively regulated.In view of this,this paper uses solvothermal reduction method to control the synthesis of five different compositions of high-phosphorus Pd_xNi_yP nanoparticles,using X-ray photoelectron spectroscopy,transmission electron microscopy and high-power transmission electron microscopy to different Pd Nanocatalysts were characterized.The valence states of Pd,Ni and P in Pd_xNi_yP ternary alloy nanoparticles with different x/y ratios were investigated,and the electronic properties of metal Pd were controlled?335.3 eV-335.9 eV?.The electronic properties of metal Pd are closely related to its ability to cleave the C-X?X=Cl,Br or I?bond.In view of this,this paper used Pd_xNi_yP/C as a catalyst to study the selective reduction of halonitrobenzene to prepare haloaniline.The selective reduction of p-chloronitrobenzene was used as a template reaction,and the conditions of the catalyst type,the amount of the reducing agent and the reaction time were selected.The effects of Pd_xNi_yP with different Pd-Ni ratios on the reaction selectivity were investigated.Control experiments were carried out using reference catalysts Pd-Ni/C,Ni/C and Pd-Cu-Ni-P/C.The experimental results show that the electropositiveness of Pd element is beneficial to improve the stability of C-Cl bond and the selectivity of p-chloroaniline at a certain Pd-Ni ratio.The amorphous Pd₃₈Ni₂₆P/C catalyst has the highest selectivity,and the isolated yield of p-chloroaniline reaches 96%.Subsequently,the range of the substrate was expanded and it was found that the Pd₃₈Ni₂₆P/C catalyst has excellent selective catalytic performance for different types of p-halonitrobenzene,and the yield of the product is50-96%.In contrast,the yield of p-halanilide was significantly reduced using Pd-Ni/C,Ni/C and Pd-Cu-Ni-P/C catalysts.The research content provides a method for realizing the valence regulation of metal electrons by constructing ternary metal phosphide,and provides a theoretical basis for the study of metal electronic valence-catalytic performance correlation.The paper has 19 reaction equations,19 figures,16 tables,and 115 references..