| The transition metal catalysts play an important role in the chemical reactions such as degradation of organic pollutants,organic synthesis and electrocatalytic reaction.However,due to the large surface free energy of metal catalysts,it is easy to agglomerate during their synthesis and using process,resulting in sintering,poisoning and decreased activity.Selecting suitable carriers to form strong metal-support interaction(SMSI)with metal catalysts can not only prevent metals from agglutinating,but also change their geometric and even surface electronic structures,which consequently improves their utilization and catalytic activity and changes the mechanism of the reaction that they catalyze.Chlorophenols are carcinogenic,teratogenic and mutagenic,so it is very important to regulate these pollutants.Furthermore,the toxicity of chlorophenols mainly results from the chlorine atoms in their molecular structure.Catalytic hydrodechlorination technology(HDC)can cleanly and efficiently remove chlorine atoms from chlorophenols molecular to reduce their toxicity,and has been widely studied.But chlorophenols cannot be completely degraded by this method.Advanced oxidation process(SR-AOPs),which uses sulfate radical(SO4·-)as the reactive oxygen species(ROS),is paid more attention because it can efficiently and thoroughly degrade chlorophenols.Highly active and stable catalysts play an important role in both the chlorophenols removal technologies.In this paper,a variety of compounds with a large number of anchoring sites were used to support precious metal Pd nanoparticles(Pd NPs,and it belongs to transition metal)and transition metal cobalt(Co)to prepare highly active catalysts with SMSI,and they were used to the 4-chlorophenol(4-CP)removal by HDC and SR-AOPs,respectively.The main research achievements are as the follows:(1)Porous aqueous ferrihydrite(Fh)containing rich hydroxyl groups was synthesized by microemulsion method,and the size of Pd NPs loaded on it was controlled at 5.39 nm.The formed SMSI between Pd and rich hydroxyl as well as iron atoms caused Pd NPs to be highly dispersive and electron-rich,and to efficiently catalyze the complete HDC degradation of 4CP in 10 min.The reaction rate constant was 0.45 min-1 and there was no obvious agglomeration and poisoning for this catalyst during the reaction process,which suggested its good stability.(2)The O-CoMoS/GO catalyst was prepared by combining the layered molybdenum disulfide(MoS2)and cobalt disulfide(CoS2)nano-flower mixture(O-CoMoS)derived from cobalt and molybdenum bimetallic polyoxometalate with graphene oxide(GO),which is rich in oxygen-containing functional groups.The catalyst could efficiently activate peroxonosulfate(PMS)to produce SO4·-,hydroxyl radicals(·OH)and singlet oxygen(1O2)for the oxidative degradation of 4-CP.There was SMSI between the Co,Mo metal active sites in the form of sulfide and GO.The GO could provide electrons to Co through the M-O-C heterojunction,which caused it to be more electron-enriched and easier to adsorb PMS molecules and ROS.As a result,O-CoMoS/GO has a high catalytic activity(the reaction rate constant is 0.54 min-1).(3)Based on the host/guest reaction between β-cyclodextrin(β-CD)and melamine(MEI),as well as the SMSI between Co and nitrogen doped carbon,Co catalysts with various existing form supported on porous nitrogen doped carbon have been successfully prepared,including Co single atom catalyst(Co SAC)with N4 coordination,ultra-small atomic Co clusters and Co nanoparticles catalysts.All of them could efficiently catalyze the oxidative degradation of 4-CP by activating PMS.Because of the different forms of Co metal and SMSI,they showed different catalytic activities for oxidative degradation of 4-CP and activated PMS to produce different proportions of active species.Since Co SAC and Co cluster have higher adsorption capacity for PMS molecules and are electron-deficient,PMS molecules with their activation are more inclined to produce superoxide radical(O2·-)and singlet oxygen(1O2)with higher selectivity for pollutant degradation,compared with the catalysis of N/C and Co nanoparticles.(4)Co SAC(Co-V-Ni(OH)2/CNT)has been prepared using the SMSI between Co and VNi(OH)2/CNT that nickel vacancy-contained nickel hydroxide supported on carbon nanotubes(CNT).Co-V-Ni(OH)2/CNT showed a high reaction rate constant(1.67 min-1)when activated PMS to degrade 4-CP,which was much higher than that of the unsupported Co-V-Ni(OH)2 by CNT.Moreover,compared with the Co(OH)2 loaded on CNT(Co(OH)2/CNT),the Co SAC in Co-V-Ni(OH)2/CNT has higher average reaction rate per unit of Co,which is due to the higher atomic utilization of Co atom and the role of Ni as a cocatalyst.Co SAC supported by different nickel compounds were prepared by treating Co-V-Ni(OH)2/CNT under different conditions to investigate the influence of coordination conditions on catalytic activity of Co SAC,and all of them were found to have high catalytic activity.Moreover,the coordination environment of Co SAC will affect its SMSI with supports,electron transfer ability and catalytic activity.Co-V-Ni(OH)2/CNT displayed higher catalytic activity than other nickel compounds supported Co SAC,which was profited from OH-on Ni(OH)2 favorable to the form of an intermediate active species of CoOH+with strong adsorption capacity to PMS molecules.In this paper,the synthesis strategies of metal catalysts supported by different carriers were designed,and the catalytic activities and mechanisms for them in the removal of 4-CP by HDC and SR-AOPs were studied.The effects of SMSI between metal catalyst and support on the structural properties(including morphological size and surface electronic structure),catalytic activity and reaction mechanism for catalysts were discussed.This provides not only reference for the basic research,development and design of highly active metal-based catalysts but also important theoretical basis for their mass industrial production,and promotes the wide practical application of HDC and AOPs technologies. |
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