Preparation Of Catalysts For Diethanolamine Dehydrogenation And Modification Of Catalysts

Iminodiacetic acid is used in the production of pesticide glyphosate,there are a variety of synthetic processes,and the most economical and environmentally friendly method is oxidative dehydrogenation of diethanolamine.The traditional Cu-based catalysts have the advantages of high activity and low price,but there are some problems to be solved.The phase structure of the carrier ZrO₂ and its related mechanism in the dehydrogenation process of diethanolamine are still not clear in frequently-used Cu/ZrO₂ catalysts.Based on this,ZrO₂ of monoclinal phase?m-?,tetrahedral phase?t-?and amorphous phase?a-?were prepared for supporting active component Cu.The physicochemical properties and catalytic activities of various catalysts were studied,especially the catalytic mechanism of Cu/m-ZrO_2.At the same time,the new catalyst supports were also studied.On the one hand,by introducing metal organic ligands?terpenic acid,TPA?to modify Cu/rGO catalysts,the feasibility of reducing graphene-supported copper based catalysts for dehydrogenation of diethanolamine was explored.On the other hand,the feasibility of Co-N-CNTs as the second carrier of Cu/ZrO₂ catalyst was explored by adding cobalt-based zeolite imidazole framework?ZIF-67?to Cu/ZrO₂ catalyst,doping Co and N elements and forming carbon nanotubes?CNTs?.Firstly,Cu/m-ZrO₂,Cu/a-ZrO₂ and Cu/t-ZrO₂ were synthesized by sedimentation method in this paper.According to the analysis results of XRD,N₂-Physical Adsorption-Desorption,XPS,H₂-TPR and CO₂-TPD,the surface electron density of Cu/m-ZrO₂ is more conducive to the stable existence of Cu⁺/Cu⁰,with more basic sites and better oxidation resistance.When the preparation conditions were as follows:copper zirconium atom ratio of 2:1,precipitation temperature of 50?,precipitation pH value=10,aging time with 12 h,the Cu/ZrO₂ catalysts showed the excellent catalytic performanc,the best reaction time reduced to 2.5 h,iminodiacetic acid yield was 97.64%.Combined with the liquid phase spectrogram,the catalytic activity centers were Cu₂O and Cu⁰.When Cu₂O content was high,more by-products were produced.Secondly,Cu/rGO catalyst was prepared by hydrothermal method,and the influence of TPA on the physical and chemical properties and catalytic properties of Cu/rGO catalyst was studied by means of XRD,FT-IR,N₂-Physical Adsorption-Desorption,XPS and dehydrogenation performance test of diethanolamine.Results showed that with ethanol and water volume ratio of 1:1 for the bases for solvent,the pH of the solution was 13.0,reaction under 160?for 10 h,GO showed the best reduction effect,the interaction between TPA and GO were the strongest,the preparation of the catalyst performance was the best,IDA yield was86.55%.SEM analysis showed that GO has a folded lamellar structure.After hydrothermal reaction,needle-like copper species were embedded in the stacked lamellar rGO.After reduction,spherical Cu₂O or Cu⁰ with particle size of about30⁶0nm were uniformly embedded or distributed in the rGO layer or surface.Finally,the prepared ZIF-67 was used as precursor,mixed with copper salt and zirconium salt to prepare Co-N-doped Cu/ZrO₂-CNTs catalyst via co-precipitation method.The results showed that after the addition of Co-N-CNTs,all of the crystallinity of m-ZrO₂,the alkaline sites on the surface of the catalyst,and the specific surface area were increased,the catalytic performance improved,and the yield of IDA increased from 82.53%to 93.47%.SEM results showed that Cu NPs with a particle size of about 76 nm was uniformly distributed on the lamellar ZrO₂carrier surface,and the diameter of CNTs were about 50 nm.