Controlled Synthesis Of Palladium Nanoparticles And Enhancement Strategy Of Electrocatalytic Hydrochlorination Reaction

Chlorinated organic compounds are common chemical raw materials which are widely used in petroleum,metallurgy,pharmaceutical,papermaking and other industries,overuse has progressively increased the amount of exposure in environment.Chlorinated contaminants are High-toxic and stable chemical structure,tough to biodegradation and facile to bioaccumulation,it’s a great menace to human health and natural environment.Electrocatalytic hydrodechlorination（EHDC）combine chemical transformation with clean and renewable electrical energy to repair chlorinated contaminants in wastewater,practices shows that EHDC has application prospects in which high degradation efficiency,simple operations,temperate reaction conditions,low-risk of secondary pollution and so on.Palladium（Pd）is the preferred noble metal catalytic material for EHDC reaction due to its moderate binding energy of Pd-H* and unique ability to activate C-Cl.However,the EHDC efficiency of simple Pd catalyst is not high and the reaction mechanism is unclear.In order to construct efficient Pd NPs catalytic materials,the Nix Al100-x-LDH,layered doubled hydroxide nanosheets,highly effective of water splitting,were introduced to construct Nix Al100-x-LDH /Pd to solve the problem of low H* production performance under alkaline conditions.And the Mo Ox nanosheets with oxygen vacancy-enriched were introduced to construct electrondeficient Pd,optimized Pd NPs electronic structure to improve EHDC efficiency.and the specific conclusions are as follows:Atomic hydrogen（H*）was generated by electrical reduction of H+ in situ,it has been deemed as the biggest contributed active species for EHDC.But in neutral or even alkaline environments,the H+ needs to be provided by water splitting.The simple Pd catalysts does not good at water splitting under alkaline conditions,so in this work,Nix Al100-x-LDH /Pd composite catalytic materials were constructed to participated the hydrogen production which Nix Al100-x-LDH of strong water splitting ability.EPR and XPS shows that the Al3+ is necessary for oxygen vacancy（Ov）formation during synthesis,and the content of Ov changes reveals a volcano-like variation with the replacement amount of Al,which reached the peak at Ni67Al33-LDH.The DFT calculation shows that the existence of Ov can improve the capacity of hydrogen production.Experimental shows that the mass activity of Ni67Al33-LDH/Pd composite is 5 times that of traditional C/Pd material（6.54 min-1 gpd-1 vs.1.20 min-1 gpd-1）.The stability of Ni67Al33-LDH/Pd catalytic materials were also investigated,and the experiments were carried out under different applied potential,different pollutant concentration and so on.Compared with other Pd based catalytic materials under similar reaction conditions reported in recent years,it has strong competitiveness.To further accomplish the application of EHDC reaction in practical wastewater,a membrane-like reactor was designed.At present,the experimental removal efficiency can reached at 1.94 g2,4-DCP gcatalyst-1 h-1,and the energy consumption is only 17.7 J mg2,4-DCP-1。.Another aspect,through the literature research,was aware of that the hydrogen evolution reaction（HER）occurs on Pd0 and hydrodechlorination reaction（HDC）occurs on Pd2+ in the process of EHDC reaction.Under the condition of hydrogen production can be satisfied,more active sites acting on the HDC reaction can effectively improve the performance of EHDC,and it has become a hot topic right now.But the Pd based materials synthesis in situ without anchoring were mostly in the state of Pd0.Therefore,introduced Mo Ox,oxygen vacancy-enriched metal oxides,was designed to stabilize the electron-deficient Pd,the Ov on Mo Ox can limits the growth of Pd NPs and form strong metal interaction between Mo-Pd,so as to optimize the formation of electron-deficient Pd.By characterizing XPS shows that the ratio of Pd2+in Mo Ox/Pd was significantly higher than that of C/Pd（the peak area ratio of Pd is that S2+/S0=0.56 vs.0.34）.EHDC performance test of Mo Ox/Pd-5%（28.86 min-1 gpd-1）shows that promoting the ratio of Pd2+ had a significant effect on optimizing the hydrodechlorination efficiency.The stability of Mo Ox/ Pd-5% catalytic materials were also investigated,and experiments under different applied potential,different pollutant concentration were carried out to provide basic experimental data for subsequent practical environmental applications.This work provides two ideas for the controllable synthesis of Pd NPs catalysts and the enhancement strategy of EHDC performance.At the same time,continuous flow experiments are carried out to simulate the actual wastewater treatment and promote the application of electrocatalytic hydrodechlorination in the actual environment.