Preparation Of Palladium-based Nanomaterials And Study On Its Electrocatalytic Hydrogenation Reduction Dechlorination Performance

Chlorophenols(CPs)are typical refractory toxic pollutants in water treatment.They are teratogenic,carcinogenic,mutagenic and genetically toxic.The aromatic ring and chlorine atom in its structure form a stable conjugated system,which leads to the environmental impact of chlorophenols.It is difficult to degrade in medium.The more chlorine atoms,the stronger the toxicity and the harder it is to be degraded.It is now listed as a priority pollutant in most countries.Among many treatment technologies,electrocatalytic hydrogenation reduction dechlorination technology(EHDC)has broad application prospects due to its high efficiency,no secondary pollution,simple operation,and mild conditions.The precious metal palladium(Pd)is an EHDC catalyst with high activity,but the low earth reserves and high price limit the application of this technology.In order to reduce the application cost and increase the catalytic activity of Pd,this paper focuses on the EHDC reaction mechanism and catalyst activity control strategy to seek faster and more efficient Pd-based catalytic materials.The Pd-based catalyst prepared in this paper is a supported catalyst,and the supports are carbon(C)and N-doped TiO₂(N/TiO₂)with different N contents,including Pd-C with different Pd exposed crystal faces and Pd-N/TiO₂with different N contents.The N/TiO₂ catalyst was characterized and analyzed by high-resolution transmission electron microscopy(HRTEM),X-ray photoelectron spectroscopy(XPS),ultraviolet-visible diffuse reflectance spectroscopy(UV-vis DRS)and X-ray diffraction(XRD).Structure,indicating structure,electronic state of elements,etc.Through the combination of experiment and theoretical calculation,the electrocatalytic hydrogenation dechlorination mechanism of metal Pd surface was explored based on the study of crystal plane dependence;the carrier effect induced by heterojunction was constructed,the electronic structure of Pd was optimized,and the electrocatalytic dechlorination performance was improved.(1)In this paper,by studying the effect of different Pd crystal faces on the electrocatalytic dechlorination performance,the catalytic surface structure on Pd was determined,and the mechanism of the electrocatalytic hydrodechlorination reaction was clarified.The EHDC performance of Pd on 2,4-dichlorophenol(2,4-DCP)was studied under the potential of-0.70?-0.95 V(vs.Ag/Ag Cl),revealing the specific active sequence of the Pd crystal face.In the potential range of-0.70?-0.80 V,Pd(110)>Pd(100)>Pd(111);in the potential range of-0.80?-0.90 V,Pd(111)>Pd(100)>Pd(110);At-0.95 V potential,Pd(111)>Pd(110)>Pd(100).By coupling these active sequences with the generation rate of active hydrogen(H^*)and the adsorption strength of 2,4-DCP and phenol(P,the main EHDC product)on the three Pd crystal faces,this paper determines that the EHDC efficiency is-0.70 It is controlled by the H^*yield at a potential of?-0.75 V,controlled by the phenol desorption kinetics of Pd at a potential of-0.80 to-0.90 V,and ionized 2,4-DCP at a potential greater than-0.95 V The electric field between the cathode and the induced repulsive force is controlled by the strength.When the crystal plane effect is further correlated with the electronic/geometric structure of Pd atoms,it is also proved that the active site density and d band center generated by H* on the surface of Pd are two key structural features that affect the efficiency of EHDC.Pd(110)with a larger active site density and Pd(111)with a lower d band center are considered to be ideal crystal planes to promote H^*generation and phenol desorption.This study provides an effective strategy for further exploring the reaction mechanism of electrocatalytic hydrodechlorination and improving the EHDC performance of Pd-based catalysts.(2)A novel strategy was constructed through the band structure of the semiconductor carrier to optimize the metal-carrier interaction at the Mott-Schottky heterojunction interface to enhance the metal electrocatalysis.In this paper,the precursor Ti N was calcined at different temperatures to prepare N-doped TiO₂semiconductors with different N contents,and then a Pd-N/TiO₂ electrocatalyst was prepared by in-situ wet chemical reduction method.The EHDC efficiency and quality activity of the catalyst are excellent.Compared with traditional Pd-C.Combined with XPS and UV analysis,it is confirmed that the forbidden band width of the semiconductor is reduced and the conduction band position is moved up.The catalyst can enhance the interface charge transfer and promote the transfer of electrons from the carrier to Pd,and the Pd in the Pd-N450 catalyst has the best electron density.So as to balance its ability to adsorb 2,4-DCP and P and improve EHDC performance.Secondly,the introduction of TiO₂ produces a hydrogen overflow effect,increases the active sites of the dechlorination reaction,and improves the utilization rate of H^*.This strategy provides a reference for the design of more efficient catalysts,and at the same time improves the economic benefits of Pd-based nanomaterial EHDC technology in the actual environmental remediation.